Carbon aerosols and atmospheric photochemistry
Journal of Geophysical Research - Atmospheres (1997)
Available from
David Lary's profile on Mendeley.
or
Abstract
Carbon aerosols are produced by all combustion processes. This paper investigates some possible effects of heterogeneous reduction of atmospheric constituents on carbon aerosols. Reduction of HNO3, NO2, and O-3 on carbon aerosols may be an important effect of increased air traffic that has not been considered to date. It is shown that if HNO3, NO2 and O-3 are heterogeneously reduced on atmospheric amorphous carbon aerosols, then a significant, lower stratospheric ozone loss mechanism could exist. This ozone loss mechanism is almost independent of temperature and does not require the presence of sunlight. The mechanism can operate at all latitudes where amorphous carbon aerosols are present. The relative importance of the mechanism increases with nightlength. The reduction of HNO3 on carbon aerosols could also be a significant renoxification process wherever carbon aerosols are present. Owing to the very different soot levels in the two hemispheres, this implies that there should be a hemispheric assymetry in the role of these mechanisms. The renoxification leads to simulated tropospheric HNO3/NOx ratios that are close to those Observed. In contrast ta the stratospheric response, the tropospheric production of NOx due to the reduction of HNO3 would lead to tropospheric ozone production.
Available from
David Lary's profile on Mendeley.
Page 1
Carbon aerosols and atmospheric photochemistry
JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 102, NO. D3, PAGES 3671-3682, FEBRUARY 20, 1997
Carbon aerosols and atmospheric photochemistry
D. J. Lary,
Renard 4
1 A.M. Lee, R. Toumi, 2 M. J. Newchurch, 3 M. Pirre, 4 and J. B.
Abstract. Carbon aerosols are produced by all combustion processes. This
paper investigates some possible effects of heterogeneous reduction of atmospheric
constituents on carbon aerosols. Reduction of HNO3, NO2, and 03 on carbon
aerosols may be an important effect of increased air traffic that has not been
considered to date. It is shown that if HNO3, NO2 and 03 are heterogeneously
reduced on atmospheric amorphous carbon aerosols, then a significant, lower
stratospheric ozone loss mechanism could exist. This ozone loss mechanism is
almost independent of temperature and does not require the presence of sunlight.
The mechanism can operate at all latitudes where amorphous carbon aerosols are
present. The relative importance of the mechanism increases with nightlength. The
reduction of HNO3 on carbon aerosols could also be a significant renoxification
process wherever carbon aerosols are present. Owing to the very different soot levels
in the two hemispheres, this implies that there should be a hemispheric assymetry
in the role of these mechanisms. The renoxification lea, ds to simulated tropospheric
HNO3/NO ratios that are close to those observed. In contrast to the stratospheric
response, the tropospheric production of NO due to the reduction of HNO3 would
lead to tropospheric ozone production.
Introduction erally overestimate the HNO3 abundance, particularly
The recent World Meteorological Organization (WMO) in the troposphere (e.g. Chatfield, 1995); third, to tro-
assessments [WMO, 1992, 1994] reported hat for the pospheric ozone production.
first time there were statistically significant decreases in
ozone in all seasons in both the northern and southern
hemispheres at mid latitudes and high latitudes during
the 1980s, and that most of this decrease occurred in
the lower stratosphere. This has also been supported by
trends derived from ozonesondes [Logan, 1994]. If this
ozone loss is due to in situ chemistry, the mechanism
involved must be able to operate at all temperatures.
In contrast to the ozone loss that occurs in the strato-
sphere, there is an observed ozone increase in the tropo-
sphere. This paper examines the role of amorphous car-
bon aerosols in reducing atmospheric onstituents. This
is relevant to several issues, including the following:
first, midlatitude, lower stratospheric ozone loss and its
temperature, altitude, and seasonal dependence; sec-
ond, to atmospheric renoxification, where models gen-
Centre For Atmospheric Science, Cambridge University, Cam-
bridge, England.
2Department of Physics, Imperial College, London, England.
3Earth System Science Laboratory, University of Alabama in
Huntsville.
4Laboratoire de Phsyique et Chimie de l'Environnement.
CNRS, Orleans. France.
Copyright 1997 by the American Geophysical Union.
Paper number 96JD02969.
0148-0227 / 97 / 96J D-02969 $ 09.00
Heterogeneous Reactions on Carbon Aerosols
Thlibi and Petit [1994] studied the interaction of soot
with NO v . They found that hydrogen atoms on the
soot surface play an important role in the interaction,
HCN being observed in the desorbed products. Thlibi
and Petit [1994] found that at the temperatures close to
those found in the atmosphere the gas/solid interaction
quickly converted both NO2 and HNOa into NO. NO
was the main product formed, with CO2, CO, N2, and
N20 being minor products. (It would therefore be in-
teresting to see if slightly larger N20 concentrations are
observed in aircraft flight corridors.) NO reacted on the
soot at a rate which was at least i order of magnitude
slower than both NO2 and HNOa.
In the presence of oxygen, NO is expected to be par-
tially converted into NO2 [Thlibi and Petit, 1994]. It is
likely that three of the NOv/soot reactions that will be
important for the atmosphere are
HNOa carb?n NO2 (1)
carbon
HNO3 NO (2)
NO2 ca-L n NO (3)
The exact fate of the oxygen and hydrogen atoms in
these processes is important and needs to be examined
3671
Carbon aerosols and atmospheric photochemistry
D. J. Lary,
Renard 4
1 A.M. Lee, R. Toumi, 2 M. J. Newchurch, 3 M. Pirre, 4 and J. B.
Abstract. Carbon aerosols are produced by all combustion processes. This
paper investigates some possible effects of heterogeneous reduction of atmospheric
constituents on carbon aerosols. Reduction of HNO3, NO2, and 03 on carbon
aerosols may be an important effect of increased air traffic that has not been
considered to date. It is shown that if HNO3, NO2 and 03 are heterogeneously
reduced on atmospheric amorphous carbon aerosols, then a significant, lower
stratospheric ozone loss mechanism could exist. This ozone loss mechanism is
almost independent of temperature and does not require the presence of sunlight.
The mechanism can operate at all latitudes where amorphous carbon aerosols are
present. The relative importance of the mechanism increases with nightlength. The
reduction of HNO3 on carbon aerosols could also be a significant renoxification
process wherever carbon aerosols are present. Owing to the very different soot levels
in the two hemispheres, this implies that there should be a hemispheric assymetry
in the role of these mechanisms. The renoxification lea, ds to simulated tropospheric
HNO3/NO ratios that are close to those observed. In contrast to the stratospheric
response, the tropospheric production of NO due to the reduction of HNO3 would
lead to tropospheric ozone production.
Introduction erally overestimate the HNO3 abundance, particularly
The recent World Meteorological Organization (WMO) in the troposphere (e.g. Chatfield, 1995); third, to tro-
assessments [WMO, 1992, 1994] reported hat for the pospheric ozone production.
first time there were statistically significant decreases in
ozone in all seasons in both the northern and southern
hemispheres at mid latitudes and high latitudes during
the 1980s, and that most of this decrease occurred in
the lower stratosphere. This has also been supported by
trends derived from ozonesondes [Logan, 1994]. If this
ozone loss is due to in situ chemistry, the mechanism
involved must be able to operate at all temperatures.
In contrast to the ozone loss that occurs in the strato-
sphere, there is an observed ozone increase in the tropo-
sphere. This paper examines the role of amorphous car-
bon aerosols in reducing atmospheric onstituents. This
is relevant to several issues, including the following:
first, midlatitude, lower stratospheric ozone loss and its
temperature, altitude, and seasonal dependence; sec-
ond, to atmospheric renoxification, where models gen-
Centre For Atmospheric Science, Cambridge University, Cam-
bridge, England.
2Department of Physics, Imperial College, London, England.
3Earth System Science Laboratory, University of Alabama in
Huntsville.
4Laboratoire de Phsyique et Chimie de l'Environnement.
CNRS, Orleans. France.
Copyright 1997 by the American Geophysical Union.
Paper number 96JD02969.
0148-0227 / 97 / 96J D-02969 $ 09.00
Heterogeneous Reactions on Carbon Aerosols
Thlibi and Petit [1994] studied the interaction of soot
with NO v . They found that hydrogen atoms on the
soot surface play an important role in the interaction,
HCN being observed in the desorbed products. Thlibi
and Petit [1994] found that at the temperatures close to
those found in the atmosphere the gas/solid interaction
quickly converted both NO2 and HNOa into NO. NO
was the main product formed, with CO2, CO, N2, and
N20 being minor products. (It would therefore be in-
teresting to see if slightly larger N20 concentrations are
observed in aircraft flight corridors.) NO reacted on the
soot at a rate which was at least i order of magnitude
slower than both NO2 and HNOa.
In the presence of oxygen, NO is expected to be par-
tially converted into NO2 [Thlibi and Petit, 1994]. It is
likely that three of the NOv/soot reactions that will be
important for the atmosphere are
HNOa carb?n NO2 (1)
carbon
HNO3 NO (2)
NO2 ca-L n NO (3)
The exact fate of the oxygen and hydrogen atoms in
these processes is important and needs to be examined
3671
Page 2
3672 LARY ET AL.: CARBON AEROSOLS AND ATMOSPHERIC PHOTOCHEMISTRY
further.
aerosols.
Direct ozone loss can also occur on carbon
crbon Oa > O2 (4)
Tabor et al. [1993, 1994] measured the accommo-
dation coefficient for NO2 uptake on solid amorphous
carbon. Like Thlibi and Petit [1994], they found that
NO2 was reduced on the solid amorphous carbon to
yield NO. If atmospheric NO2 is reduced in this way on
solid amorphous carbon then it represents a significant
nighttime loss of Os as the reduction of NO2 is actually
the rate limiting step of the catalytic cycle
carbon
NO > NO
NO+Oa > NO+O (5)
carbon
NetOs 02
This ozone loss cycle is unusual in that it can occur
during the night. It does not require the presence of
sunlight. However, the cycle also proceeds during the
day. The cycle has little effect on other NO v species
because as soon as the NO is formed it is almost im-
mediately converted back in to NO2. This cycle should
play a role whenever there are carbon aerosols. There
is, of course, the possibility that the active sites for ph-
ysisorption will become saturated and so will take no
further part in the heterogeneous process. If this is
the case, then desorption could be initiated by heating
and the presence of UV light. Another important issue
is whether oxygen atoms are produced; if they are, this
may partially or completely negate the ozone loss mech-
anism just described. These are all areas that need to
be further investigated.
Tabor et al. [1993, 1994] report an accommodation
coefficient for NO2 uptake on solid amorphous carbon
of (4.8 4- 0.6) x 10 -2. They found that the only ma-
jor product was NO corresponding to about 60% of the
NO2 adsorbed on the surface. Consequently, in this
study, a '/value for the heterogeneous reduction of NO2
to NO of 2.8 x 10 -2 was used. Thlibi and Petit [1994]
found that the reduction of HNOs into NO also oc-
curs on carbon aerosols. Rogaski et al. [1996, also per-
sonal communication, 1996] measured an uptake value
of (3.8 4- 0.8) x 10 -2. For the length of their exper-
iments (<45 min) they observed no time dependence.
They found that the major products of the heteroge-
neous interaction of HNOs with soot were H20, NO2,
and NO. They looked for O2 and N2 production but did
not observe any. They determined the product yield for
each species. NO2 was the dominant NO product. It
was a factor of 5 larger than the NO yield. They mea-
sured that, on average, for every three HNOa molecules
lost to the surface, two NOx molecules are released to
the atmosphere. Consequently, in this study, a sticking
coefficient of 4.2 x 10 -s was used for HNOs to NO con-
version and a sticking coefficient of 2.1 x 10 -2 was used
for HNOs to NO2 conversion.
The evaluation of DeMote et al. [1994] recommends
a reaction probability for Os on carbon/soot of 3 x
10 -2. Fendel and Ott [1993] report fast Os loss on 10
to 100 nm solid carbon agglomerates, with an estimated
reaction probability near 3 x 10-2. Fendel et al. [1995]
report that submicron carbon or iron aerosol particles
destroy ozone efficiently; the sticking coefficient of Os
to the particles is of the order of 10 -4 . They conclude
that particles present in the stratosphere may repre-
sent a significant sink for Os. Smith et al. [1988] re-
port that the ozone/soot reaction is first order in ozone,
with CO, CO2 and H20 the only stable gaseous prod-
ucts. Stephens et al. [1986] measured CO, CO2 and
O2 as products with an O2 produced for each O3 re-
acted. Stephens et al. [1986] measured uptake coef-
ficients which varied from 10 -s to 10 -5 depending on
the carbon sample and Os exposure. The Os reaction
probability on carbon aerosols is clearly dependent on
the carbon aerosol's surface history. Consequently, in
this study, a sticking coefficient of 1 x 10 -5 was used
for Os to O2 conversion as a lower limit, so that the
effects on the ozone should be at least those reported
here, and, in fact, will probably be greater.
Production, Transport, and Characteristics of
Carbon Aerosols
Atmospheric soot particles are produced by the in-
complete combustion of fossil and other fuels. Com-
bustion generated aerosols can affect the atmosphere in
two main ways, via light absorption (e.g., Shaw and
Stamnes, 1980; Porch and MacCracken, 1982; Cess,
1983; Rosen and Hansen, 1984) and via heterogeneous
reactions on their surfaces (e.g., Tabor et al., 1993,
1994). Heterogeneous reduction of atmospheric on-
stituents on carbon aerosols is a possibility that has
been largely overlooked up until now, but it could ac-
tually be very important.
The present subsonic air traffic occurs mainly in the
northern hemisphere, with about 30% to 50% flying
above the tropopause [Schumann, 1994]. Future high-
speed civil transport (HSCT) systems have been pro-
posed to fly in the middle and lower stratosphere. In
1990, about 176 Mt of aviation fuel was used. To put
this into context, this aviation fuel constitutes about 6%
of all petrol products and provides about 3% of the CO2
released by the burning of fossil fuels. Global fuel con-
sumption grows by about 3% per year, with a doubling
expected within the next 18 to 25 years. Present emis-
sions by space flight are about a factor of 10,000 times
smaller than those from aviation. The present avia-
tion traffic has already caused a considerable increase
in NO concentrations (between 30% to 100%) in the
upper troposphere along main flight routes [Schumann,
Graphitic carbon particles can be transported on the
global scale and so are able to reach remote regions.
Long-range transport of graphitic carbon particles of
further.
aerosols.
Direct ozone loss can also occur on carbon
crbon Oa > O2 (4)
Tabor et al. [1993, 1994] measured the accommo-
dation coefficient for NO2 uptake on solid amorphous
carbon. Like Thlibi and Petit [1994], they found that
NO2 was reduced on the solid amorphous carbon to
yield NO. If atmospheric NO2 is reduced in this way on
solid amorphous carbon then it represents a significant
nighttime loss of Os as the reduction of NO2 is actually
the rate limiting step of the catalytic cycle
carbon
NO > NO
NO+Oa > NO+O (5)
carbon
NetOs 02
This ozone loss cycle is unusual in that it can occur
during the night. It does not require the presence of
sunlight. However, the cycle also proceeds during the
day. The cycle has little effect on other NO v species
because as soon as the NO is formed it is almost im-
mediately converted back in to NO2. This cycle should
play a role whenever there are carbon aerosols. There
is, of course, the possibility that the active sites for ph-
ysisorption will become saturated and so will take no
further part in the heterogeneous process. If this is
the case, then desorption could be initiated by heating
and the presence of UV light. Another important issue
is whether oxygen atoms are produced; if they are, this
may partially or completely negate the ozone loss mech-
anism just described. These are all areas that need to
be further investigated.
Tabor et al. [1993, 1994] report an accommodation
coefficient for NO2 uptake on solid amorphous carbon
of (4.8 4- 0.6) x 10 -2. They found that the only ma-
jor product was NO corresponding to about 60% of the
NO2 adsorbed on the surface. Consequently, in this
study, a '/value for the heterogeneous reduction of NO2
to NO of 2.8 x 10 -2 was used. Thlibi and Petit [1994]
found that the reduction of HNOs into NO also oc-
curs on carbon aerosols. Rogaski et al. [1996, also per-
sonal communication, 1996] measured an uptake value
of (3.8 4- 0.8) x 10 -2. For the length of their exper-
iments (<45 min) they observed no time dependence.
They found that the major products of the heteroge-
neous interaction of HNOs with soot were H20, NO2,
and NO. They looked for O2 and N2 production but did
not observe any. They determined the product yield for
each species. NO2 was the dominant NO product. It
was a factor of 5 larger than the NO yield. They mea-
sured that, on average, for every three HNOa molecules
lost to the surface, two NOx molecules are released to
the atmosphere. Consequently, in this study, a sticking
coefficient of 4.2 x 10 -s was used for HNOs to NO con-
version and a sticking coefficient of 2.1 x 10 -2 was used
for HNOs to NO2 conversion.
The evaluation of DeMote et al. [1994] recommends
a reaction probability for Os on carbon/soot of 3 x
10 -2. Fendel and Ott [1993] report fast Os loss on 10
to 100 nm solid carbon agglomerates, with an estimated
reaction probability near 3 x 10-2. Fendel et al. [1995]
report that submicron carbon or iron aerosol particles
destroy ozone efficiently; the sticking coefficient of Os
to the particles is of the order of 10 -4 . They conclude
that particles present in the stratosphere may repre-
sent a significant sink for Os. Smith et al. [1988] re-
port that the ozone/soot reaction is first order in ozone,
with CO, CO2 and H20 the only stable gaseous prod-
ucts. Stephens et al. [1986] measured CO, CO2 and
O2 as products with an O2 produced for each O3 re-
acted. Stephens et al. [1986] measured uptake coef-
ficients which varied from 10 -s to 10 -5 depending on
the carbon sample and Os exposure. The Os reaction
probability on carbon aerosols is clearly dependent on
the carbon aerosol's surface history. Consequently, in
this study, a sticking coefficient of 1 x 10 -5 was used
for Os to O2 conversion as a lower limit, so that the
effects on the ozone should be at least those reported
here, and, in fact, will probably be greater.
Production, Transport, and Characteristics of
Carbon Aerosols
Atmospheric soot particles are produced by the in-
complete combustion of fossil and other fuels. Com-
bustion generated aerosols can affect the atmosphere in
two main ways, via light absorption (e.g., Shaw and
Stamnes, 1980; Porch and MacCracken, 1982; Cess,
1983; Rosen and Hansen, 1984) and via heterogeneous
reactions on their surfaces (e.g., Tabor et al., 1993,
1994). Heterogeneous reduction of atmospheric on-
stituents on carbon aerosols is a possibility that has
been largely overlooked up until now, but it could ac-
tually be very important.
The present subsonic air traffic occurs mainly in the
northern hemisphere, with about 30% to 50% flying
above the tropopause [Schumann, 1994]. Future high-
speed civil transport (HSCT) systems have been pro-
posed to fly in the middle and lower stratosphere. In
1990, about 176 Mt of aviation fuel was used. To put
this into context, this aviation fuel constitutes about 6%
of all petrol products and provides about 3% of the CO2
released by the burning of fossil fuels. Global fuel con-
sumption grows by about 3% per year, with a doubling
expected within the next 18 to 25 years. Present emis-
sions by space flight are about a factor of 10,000 times
smaller than those from aviation. The present avia-
tion traffic has already caused a considerable increase
in NO concentrations (between 30% to 100%) in the
upper troposphere along main flight routes [Schumann,
Graphitic carbon particles can be transported on the
global scale and so are able to reach remote regions.
Long-range transport of graphitic carbon particles of
Page 3
LARY ET AL.- CARBON AEROSOLS AND ATMOSPHERIC PHOTOCHEMISTRY 3673
at least 2000 km from the closest significant source re-
gion has been observed at ground level stations through-
out the western Arctic [Stonehouse, 1986; Rosen et al.,
1981; Heintzenber9, 1982; Rosen and Novakov, 1983].
Trace element and meteorological analyses suggest hat
even longer-range transport from midlatitudes between
5,000 and 10,000 km away had taken place [Rahn and
McCaffrey, 1980; Bartie et al., 1981].
Horizontal profiles of graphitic carbon particles have
been provided by missions such as the National Oceano-
graphic and Atmospheric Administration (NOAA) air-
plane sampling programme during March and April
1983 [Schnell et al., 1994; Rosen and Hansen, 1984;
Hansen and Rosen, i984]. it has been found that
graphitic carbon particles are present throughout the
arctic troposphere with upper layers typically contain-
ing more particles than at ground level.
Pusechel et al. [1992] reported that upper tropo-
spheric aircraft emissions of soot presently represent
approximately 0.3% by mass of the background strato-
spheric aerosols. Blake and Karo [1995] recently pre-
sented an overview of black carbon soot measurements
made in the upper troposphere and lower stratosphere,
k.-,+ ...... ArOq ,A ONONT nncl they annfirm thi,q finclinp'.
They also point out that for volcanically quiescent peri-
ods, if surface areas are considered instead of mass, the
surface area of carbon aerosols is comparable to that of
sulphate aerosols. In fact, the surface area of carbon
aerosols may be more than that of sulphate aerosols
during volcanically quiescent periods. This is because
carbon aerosols are typically not spherical, but rather
have a fractal geometry. Blake and Karo [1995] consid-
ered two extreme cases and calculated the surface area
of the carbon particles as if they were all spheres or as if
they had a purely fractal geometry. The fractal surface
area calculation gave an area that was 30 times greater
than the area calculated if all the carbon aerosols were
assumed to be 20 nm spheres.
Colbeck and Nyeki [1992] presented a review of fractal
structures as applied to environmental aerosols. They
point out that the atmospheric lifetime of particles is
dependent on their terminal velocity, which is related to
the fractal dimension of the particles. Many natural ob-
jects such as coastlines and clouds may be represented
by fractal theory. A basic property of fractal objects is
that they obey the scaling relationship'
N oc B D (6)
where N is the number of features, R is the resolution
of measurements, and D is the fractal dimension of the
object. Fractal clusters sediment more slowly than com-
pact spheres of the same mass. Berry [1989] calculated
that clusters composed of 1000 individual spherules of
radius 20 nm fall at approximately 100 m yr - if D:1.8
as compared with i km yr - for solid clusters (D:3).
Blake and Kato [1995] state that the carbon aerosol
distributions they presented did not account for soot
that had been entrained within sulphuric acid droplets.
It is rather surprising that most of the soot aerosols are
not actually entrained in sulphate aerosols. Blake and
Kato [1995] speculated that aircraft-generated aerosols
may constitute poor condensation nuclei. However,
Kiircher et al. [1996] find strong evidence that aircraft
soot is responsible for the buildup of visible contrails.
KSrcher et al. [1996] show that the observation is con-
sistent with model results under the assumption that
soot gets coated by a liquid H2SO4/H20 solution, pos-
sibly also containing HNOa, and that the soot core trig-
gers heterogeneous freezing of water ice during plume
cooling. They found that the observations cannot be ex-
plained by assuming dry soot upon which ice nucleates
results strongly point toward the fact that aircraft soot
leaves the jet engines already entrained in a liquid sul-
furic acid solution. This is also very likely to be true in
cases where no visible ice contrails form. Even if soot
would be emitted without coating, quick coagulation
processes with in situ nucleated H2SO4/H20 aerosols
might entrain them into droplets. This would be simi-
lar to the Kuwaiti oil fire plumes studied by, for exam-
ple, Parun9o et al. [1992], where carbon had become
entrained within liquid droplets. It could be that the
soot is entrained in droplets close to the aircraft, but in
the far-field situation as measured by Blake and Karo
[1995], the soot is no longer entrained within a droplet.
It seems that biomass burning does not contribute
significantly to the upper tropospheric, lower strato-
spheric soot loading. Blake and Karo [1995] found that
the measured latitudinal distribution of black carbon
soot between 10 and 11 km covaried with commercial
air traffic use, suggesting that aircraft fuel combustion
is the principal source of soot at this altitude. In ad-
dition, they found that at latitudes where there is a
lot of commercial air traffic, significant levels of black
carbon soot were measured even at 20 km. This sug-
gests that aircraft-generated soot injected just above
the tropopause may be transported to higher altitudes.
By assigning upper and lower estimates on the total
fuel burned in the stratosphere by aircraft and compar-
ing this to the measured soot concentrations, a black
carbon soot residence time of between 4 and 12 months
was derived by Blake and Karo [1995].
Baum#ardner et al. [1996] report results from a new
instrument which can simultaneously measure aerosol
diameter between 0.4 and 10 ttm and which was recently
flown on the NASA ER2 aircraft during a stratospheric
measurement campaign. The measured stratospheric
refractive indices do not agree well with theoretical pre-
dictions, and vertical profiles suggest the presence of
nonspherical or absorbing particles in the altitude range
of 7 to 9 km. One possibility is that Baumgardner et
al. [1996] observed carbon aerosols.
In the Arctic boundary layer a low HNOa/NOx ratio
has been inferred from measurements. Therefore, if the
soot reduction actually occurs, since the Arctic is where
soot accumulates, we would expect to see the low values
at least 2000 km from the closest significant source re-
gion has been observed at ground level stations through-
out the western Arctic [Stonehouse, 1986; Rosen et al.,
1981; Heintzenber9, 1982; Rosen and Novakov, 1983].
Trace element and meteorological analyses suggest hat
even longer-range transport from midlatitudes between
5,000 and 10,000 km away had taken place [Rahn and
McCaffrey, 1980; Bartie et al., 1981].
Horizontal profiles of graphitic carbon particles have
been provided by missions such as the National Oceano-
graphic and Atmospheric Administration (NOAA) air-
plane sampling programme during March and April
1983 [Schnell et al., 1994; Rosen and Hansen, 1984;
Hansen and Rosen, i984]. it has been found that
graphitic carbon particles are present throughout the
arctic troposphere with upper layers typically contain-
ing more particles than at ground level.
Pusechel et al. [1992] reported that upper tropo-
spheric aircraft emissions of soot presently represent
approximately 0.3% by mass of the background strato-
spheric aerosols. Blake and Karo [1995] recently pre-
sented an overview of black carbon soot measurements
made in the upper troposphere and lower stratosphere,
k.-,+ ...... ArOq ,A ONONT nncl they annfirm thi,q finclinp'.
They also point out that for volcanically quiescent peri-
ods, if surface areas are considered instead of mass, the
surface area of carbon aerosols is comparable to that of
sulphate aerosols. In fact, the surface area of carbon
aerosols may be more than that of sulphate aerosols
during volcanically quiescent periods. This is because
carbon aerosols are typically not spherical, but rather
have a fractal geometry. Blake and Karo [1995] consid-
ered two extreme cases and calculated the surface area
of the carbon particles as if they were all spheres or as if
they had a purely fractal geometry. The fractal surface
area calculation gave an area that was 30 times greater
than the area calculated if all the carbon aerosols were
assumed to be 20 nm spheres.
Colbeck and Nyeki [1992] presented a review of fractal
structures as applied to environmental aerosols. They
point out that the atmospheric lifetime of particles is
dependent on their terminal velocity, which is related to
the fractal dimension of the particles. Many natural ob-
jects such as coastlines and clouds may be represented
by fractal theory. A basic property of fractal objects is
that they obey the scaling relationship'
N oc B D (6)
where N is the number of features, R is the resolution
of measurements, and D is the fractal dimension of the
object. Fractal clusters sediment more slowly than com-
pact spheres of the same mass. Berry [1989] calculated
that clusters composed of 1000 individual spherules of
radius 20 nm fall at approximately 100 m yr - if D:1.8
as compared with i km yr - for solid clusters (D:3).
Blake and Kato [1995] state that the carbon aerosol
distributions they presented did not account for soot
that had been entrained within sulphuric acid droplets.
It is rather surprising that most of the soot aerosols are
not actually entrained in sulphate aerosols. Blake and
Kato [1995] speculated that aircraft-generated aerosols
may constitute poor condensation nuclei. However,
Kiircher et al. [1996] find strong evidence that aircraft
soot is responsible for the buildup of visible contrails.
KSrcher et al. [1996] show that the observation is con-
sistent with model results under the assumption that
soot gets coated by a liquid H2SO4/H20 solution, pos-
sibly also containing HNOa, and that the soot core trig-
gers heterogeneous freezing of water ice during plume
cooling. They found that the observations cannot be ex-
plained by assuming dry soot upon which ice nucleates
results strongly point toward the fact that aircraft soot
leaves the jet engines already entrained in a liquid sul-
furic acid solution. This is also very likely to be true in
cases where no visible ice contrails form. Even if soot
would be emitted without coating, quick coagulation
processes with in situ nucleated H2SO4/H20 aerosols
might entrain them into droplets. This would be simi-
lar to the Kuwaiti oil fire plumes studied by, for exam-
ple, Parun9o et al. [1992], where carbon had become
entrained within liquid droplets. It could be that the
soot is entrained in droplets close to the aircraft, but in
the far-field situation as measured by Blake and Karo
[1995], the soot is no longer entrained within a droplet.
It seems that biomass burning does not contribute
significantly to the upper tropospheric, lower strato-
spheric soot loading. Blake and Karo [1995] found that
the measured latitudinal distribution of black carbon
soot between 10 and 11 km covaried with commercial
air traffic use, suggesting that aircraft fuel combustion
is the principal source of soot at this altitude. In ad-
dition, they found that at latitudes where there is a
lot of commercial air traffic, significant levels of black
carbon soot were measured even at 20 km. This sug-
gests that aircraft-generated soot injected just above
the tropopause may be transported to higher altitudes.
By assigning upper and lower estimates on the total
fuel burned in the stratosphere by aircraft and compar-
ing this to the measured soot concentrations, a black
carbon soot residence time of between 4 and 12 months
was derived by Blake and Karo [1995].
Baum#ardner et al. [1996] report results from a new
instrument which can simultaneously measure aerosol
diameter between 0.4 and 10 ttm and which was recently
flown on the NASA ER2 aircraft during a stratospheric
measurement campaign. The measured stratospheric
refractive indices do not agree well with theoretical pre-
dictions, and vertical profiles suggest the presence of
nonspherical or absorbing particles in the altitude range
of 7 to 9 km. One possibility is that Baumgardner et
al. [1996] observed carbon aerosols.
In the Arctic boundary layer a low HNOa/NOx ratio
has been inferred from measurements. Therefore, if the
soot reduction actually occurs, since the Arctic is where
soot accumulates, we would expect to see the low values
Page 4
3674 LARY ET AL.' CARBON AEROSOLS AND ATMOSPHERIC PHOTOCHEMISTRY
that are seen. The observations therefore subjectively
support the reduction of HNO3 on soot.
These findings point to the potential importance of
NOu/amorphous carbon interactions on the local and
global scale in the stratosphere and the troposphere. If
the aviation fuel consumption is set to double in the
next 18 to 25 years, it is likely that the carbon surface
area will also double, while increases of up to a factor
of 10 could occur in flight corridors [WMO, 1994]. This
opens the possibility that on the hemispheric scale the
carbon surface area could be double that of the back-
ground sulphate aerosol surface area during volcanically
quiescent periods, and 10 times that of the background
sulphate aerosol surface area in flight corridors. Such a
large surface area could therefore be a potentially im-
portant site for heterogeneous atmospheric chemistry,
which really should be thoroughly investigated with a
sense of urgency.
It is not only nitrogen species that could be reduced
on carbon aerosols. For example, HOC1 could be re-
duced to HC1, and HOBr could be reduced to HBr. This
could be significant in polar regions, where the produc-
tion of HC1 can become the rate limiting step for further
chlorine activation. These processes also need detailed
examination.
Comparison With Observations
Since there is uncertainty associated with the rate at
which HNO3 and NO2 is reduced on carbon aerosols,
this section compares some observations with model
culations that include the reduction of HN03 and NO2
on carbon aerosols.
SESAME Comparison
Figure 1 shows three simulations that were performed
with a three-dimensional chemical transport model [Chip-
perfield et al., 1996], which used meteorological analy-
ses to specify the circulation. The model was integrated
for 12 days and used results from a seasonal integration,
which had been integrated from November 22, 1994, in
order to initialize each simulation. The seasonal inte-
gration had been initialized itself from a combination of
two-dimensional chemical fields and data from instru-
ments on board the UARS satellite. This integration is
presently being used to investigate the anomalously low
03 amounts seen during the 1994/1995 northern winter
(as observed by Mannel et al. [1996]). The model was
sampled during each simulation at the same time and
position relevant to measurements of NO2 made by 'Ab-
sorption par Minoritaires Ozone et NOx' (AMON) at
night inside the polar vortex on February 10, 1995, over
Kiruna during the Second European Stratospheric Arc-
tic and Mid-latitude Experiment (SESAME)campaign
[Hermann et al., 1996].
Simulation A was a control simulation that includes
a standard stratospheric chemistry scheme without any
10-
lOO
-
1000
0.001
profiles over Kiruna
i i i I illill i , i iiiiill ii i i i iiiiii t
., !
/
ß AMON data Simulation A
........ Simulation B Simulation C -
_
0.01 0.1 1.0 10.0
(ppbv)
Figure 1. Second European Stratospheric Arctic and
Mid-latitude Experiment (SESAME) campaign com-
parison for the simulated NO2 profiles over Kiruna on
February 10, 1995. Simulation A (solid line) was a con-
trol simulation which includes a standard stratospheric
chemistry scheme. Simulation B (dashed line) included
the reduction of HNO3 and NO2 on carbon aerosols,
both with a 7 value of 2.8 x 10 -2 and a carbon aerosol
surface area of 1 tzm2/cm 3.Simulation C (dot-dashed
line) was the same as simulation B, except he 7 value
for the reduction of HNO3 was reduced by a factor of
10.
heterogeneous carbon reactions. Simulation B includes
the reduction of HNO3 and NO2 on carbon aerosols,
both with a 7 value of 2.8 x 10 -2. Simulation C was
the same as simulation B, except the 7 value for the
reduction of HNO3 was reduced by a factor of 10 to
a value of 2.8 x 10 -3. The simulations included the
hydrolysis of N205, C1ONO2, and BrONO2 on sulphate
aerosols.
Figure 1 shows that the NO2 observations are brack-
eted by simulations that included heterogeneous carbon
reactions (simulations B and C). This is not conclusive
proof that the proposed carbon mechanism does occur,
but it does make it clear that without some kind of
renoxification mechanism, whether it is the mechanism
postulated here or some other mechanism, the vertical
profiles of NO2 are not well simulated when the hydroly-
sis of N205 on sulphate aerosols is included. The N20,
hydrolysis used in this study is the temperature and
composition dependent data recommended by DeMote
et al. [1994]. A slower N20, hydrolysis on sulphate
aerosols would clearly also increase the simulated NOx
concentration. The required renoxification mechanism
needs to operate up to altitudes of around 25 to 30 km.
It is unclear what the transport mechanism would be
for carbon aerosol to be found at these altitudes within
the polar vortex.
that are seen. The observations therefore subjectively
support the reduction of HNO3 on soot.
These findings point to the potential importance of
NOu/amorphous carbon interactions on the local and
global scale in the stratosphere and the troposphere. If
the aviation fuel consumption is set to double in the
next 18 to 25 years, it is likely that the carbon surface
area will also double, while increases of up to a factor
of 10 could occur in flight corridors [WMO, 1994]. This
opens the possibility that on the hemispheric scale the
carbon surface area could be double that of the back-
ground sulphate aerosol surface area during volcanically
quiescent periods, and 10 times that of the background
sulphate aerosol surface area in flight corridors. Such a
large surface area could therefore be a potentially im-
portant site for heterogeneous atmospheric chemistry,
which really should be thoroughly investigated with a
sense of urgency.
It is not only nitrogen species that could be reduced
on carbon aerosols. For example, HOC1 could be re-
duced to HC1, and HOBr could be reduced to HBr. This
could be significant in polar regions, where the produc-
tion of HC1 can become the rate limiting step for further
chlorine activation. These processes also need detailed
examination.
Comparison With Observations
Since there is uncertainty associated with the rate at
which HNO3 and NO2 is reduced on carbon aerosols,
this section compares some observations with model
culations that include the reduction of HN03 and NO2
on carbon aerosols.
SESAME Comparison
Figure 1 shows three simulations that were performed
with a three-dimensional chemical transport model [Chip-
perfield et al., 1996], which used meteorological analy-
ses to specify the circulation. The model was integrated
for 12 days and used results from a seasonal integration,
which had been integrated from November 22, 1994, in
order to initialize each simulation. The seasonal inte-
gration had been initialized itself from a combination of
two-dimensional chemical fields and data from instru-
ments on board the UARS satellite. This integration is
presently being used to investigate the anomalously low
03 amounts seen during the 1994/1995 northern winter
(as observed by Mannel et al. [1996]). The model was
sampled during each simulation at the same time and
position relevant to measurements of NO2 made by 'Ab-
sorption par Minoritaires Ozone et NOx' (AMON) at
night inside the polar vortex on February 10, 1995, over
Kiruna during the Second European Stratospheric Arc-
tic and Mid-latitude Experiment (SESAME)campaign
[Hermann et al., 1996].
Simulation A was a control simulation that includes
a standard stratospheric chemistry scheme without any
10-
lOO
-
1000
0.001
profiles over Kiruna
i i i I illill i , i iiiiill ii i i i iiiiii t
., !
/
ß AMON data Simulation A
........ Simulation B Simulation C -
_
0.01 0.1 1.0 10.0
(ppbv)
Figure 1. Second European Stratospheric Arctic and
Mid-latitude Experiment (SESAME) campaign com-
parison for the simulated NO2 profiles over Kiruna on
February 10, 1995. Simulation A (solid line) was a con-
trol simulation which includes a standard stratospheric
chemistry scheme. Simulation B (dashed line) included
the reduction of HNO3 and NO2 on carbon aerosols,
both with a 7 value of 2.8 x 10 -2 and a carbon aerosol
surface area of 1 tzm2/cm 3.Simulation C (dot-dashed
line) was the same as simulation B, except he 7 value
for the reduction of HNO3 was reduced by a factor of
10.
heterogeneous carbon reactions. Simulation B includes
the reduction of HNO3 and NO2 on carbon aerosols,
both with a 7 value of 2.8 x 10 -2. Simulation C was
the same as simulation B, except the 7 value for the
reduction of HNO3 was reduced by a factor of 10 to
a value of 2.8 x 10 -3. The simulations included the
hydrolysis of N205, C1ONO2, and BrONO2 on sulphate
aerosols.
Figure 1 shows that the NO2 observations are brack-
eted by simulations that included heterogeneous carbon
reactions (simulations B and C). This is not conclusive
proof that the proposed carbon mechanism does occur,
but it does make it clear that without some kind of
renoxification mechanism, whether it is the mechanism
postulated here or some other mechanism, the vertical
profiles of NO2 are not well simulated when the hydroly-
sis of N205 on sulphate aerosols is included. The N20,
hydrolysis used in this study is the temperature and
composition dependent data recommended by DeMote
et al. [1994]. A slower N20, hydrolysis on sulphate
aerosols would clearly also increase the simulated NOx
concentration. The required renoxification mechanism
needs to operate up to altitudes of around 25 to 30 km.
It is unclear what the transport mechanism would be
for carbon aerosol to be found at these altitudes within
the polar vortex.
Page 5
LARY ET AL' CARBON AEROSOLS AND ATMOSPHERIC PHOTOCHEMISTRY 3675
44.6 ø N, 140.3 ø E, 7:17 GMT, 6 November 1994
ß ATMOS Data 0 m2/cm soot ............. 0.1 fi, m%m soot
..... 0.2/.zm%m soot 0.5 fi, m%m soot- ..... I/m2/cm soot
35
15-
_
10 {
0.03 0.06 0.1
-35
-30
_
_
_
_
_
_
_
_
_
_15
-10
35-
_
_
_
30--
_
'O -
::3 -
-
_
_
15--
_
_
_
10-
0.01
77.1 o S, 147.1 o E, 15:46 GMT, 9 November 1994
ß ATMOS Data 0 m2/cm soot ............. 0 1/m2/cm soot
..... 0.2/.zm%m soot 0.5 fi, m2/cm soot- ..... I/.zm%m soot
I
I
o.o3 o.06 0.1 0.3 o.6 1.o
HNOJNO HNOJNO
-35
30
25
{
I
I -2O
L5
3.0 6 0 10.0
Figure 1. Second European Stratospheric Arctic and Mid-latitude Experiment (SESAME) cam-
paign comparison for the simulated NO2 profiles over Kiruna on February 10, 1995. Simulation
A (solid line) was a control simulation which includes a standard stratospheric hemistry scheme.
Simulation B (dashed line) included the reduction of HNOa and NO2 on carbon aerosols, both
with a 7 value of 2.8 x 10 -2 and a carbon aerosol surface area of 1 pm2/cm 3. Simulation C
(dot-dashed line) was the same as simulation B, except the 7 value for the reduction of HNOa
was reduced by a factor of 10.
ATMOS ATLAS3 Comparison
Figure 2 shows the effect of the reduction of HNO3
and NOa on carbon aerosols (Table 1) on the vertical
profiles of NOa and the HNO3/NO: ratio in the north-
ern and southern hemispheres compared to the Atmo-
spheric Trace Molecule Spectroscopy (ATMOS) Exper-
iment ATLAS3 measurements made during November
1994. The model used was the AUTOCHEM column
model described by Lary [1996] and Lary et al. [1995,
1996]. The column model was run for 7 days starting
from the ATMOS ATLAS3 vertical profiles of temper-
ature, 03, NO, NO2, N205, HNO3, HNO4, C1ONOa,
H20, CO, CO2, CH4 and NaO. Below 25 km the di-
urnal correction to the NO2 profiles is very important
[Newchurch et al., 1996].
It can be seen from Figure 2 that above 25 km there is
excellent agreement between the model and the observa-
tions in both hemispheres. Below 25 km there is a slight
contrast between the hemispheres. As noted above,
Table 1. Carbon Reduction Reactions Included in
This Study
Reaction 7 used
carbon HNO3 > NO2 2.1 x 10 -2
carbon HNO3 > NO 4.2 x 10 -3
carbon NO2 > NO 2.8 x 10 -2
carbon 03 > 02 1 x 10 -s
the northern hemisphere has a larger soot loading than
the southern hemisphere. The best agreement between
the model simulations and the ATMOS ATLAS3 ob-
servations in the northern hemisphere falls close to the
simulation with 0.2/m2/cm 3. This is in general agree-
ment with the SESAME comparison described above.
In contrast, the best agreement between the model sim-
ulations and the ATMOS ATLAS3 observations in the
southern hemisphere falls close to the simulation with
0.1/m2/cm 3. This is consistent with the fact that the
southern hemisphere has a lower soot loading. Figure 2
also shows how sensitive the HNO3/NOx ratio is to the
soot loading. An increase of the soot loading by a fac-
tor of 10 reduces the HNO3/NOx ratio by a factor of
approximately 100 in the lower stratosphere. Includ-
ing the reduction of HNO3 on soot leads to a simulated
HNOa/NOx ratio within the observed range of the aver-
age free tropospheric ratio of 1-9 reported by Chatfield
[1995].
.... c comparisons not conclusively prove that the
reduction on carbon aerosols actually occurs but they
show that the reduction of NO2 and HNO3 is at least
consistent with observations and can explain the hemi-
spheric assymetry in the observed NO2 and HNOa/NO
ratio vertical profiles. To say this another way, a renox-
ification mechanism, whether it is the one postulated
here or a completely different mechanism, can improve
the agreement between observations and simulations of
the observed NO s partitioning if it is more effective in
the northern hemisphere than the southern hemisphere.
Toumi et al. [1993] considered the ATMOS HNO3/
NO ratio and concluded that the current recommen-
44.6 ø N, 140.3 ø E, 7:17 GMT, 6 November 1994
ß ATMOS Data 0 m2/cm soot ............. 0.1 fi, m%m soot
..... 0.2/.zm%m soot 0.5 fi, m%m soot- ..... I/m2/cm soot
35
15-
_
10 {
0.03 0.06 0.1
-35
-30
_
_
_
_
_
_
_
_
_
_15
-10
35-
_
_
_
30--
_
'O -
::3 -
-
_
_
15--
_
_
_
10-
0.01
77.1 o S, 147.1 o E, 15:46 GMT, 9 November 1994
ß ATMOS Data 0 m2/cm soot ............. 0 1/m2/cm soot
..... 0.2/.zm%m soot 0.5 fi, m2/cm soot- ..... I/.zm%m soot
I
I
o.o3 o.06 0.1 0.3 o.6 1.o
HNOJNO HNOJNO
-35
30
25
{
I
I -2O
L5
3.0 6 0 10.0
Figure 1. Second European Stratospheric Arctic and Mid-latitude Experiment (SESAME) cam-
paign comparison for the simulated NO2 profiles over Kiruna on February 10, 1995. Simulation
A (solid line) was a control simulation which includes a standard stratospheric hemistry scheme.
Simulation B (dashed line) included the reduction of HNOa and NO2 on carbon aerosols, both
with a 7 value of 2.8 x 10 -2 and a carbon aerosol surface area of 1 pm2/cm 3. Simulation C
(dot-dashed line) was the same as simulation B, except the 7 value for the reduction of HNOa
was reduced by a factor of 10.
ATMOS ATLAS3 Comparison
Figure 2 shows the effect of the reduction of HNO3
and NOa on carbon aerosols (Table 1) on the vertical
profiles of NOa and the HNO3/NO: ratio in the north-
ern and southern hemispheres compared to the Atmo-
spheric Trace Molecule Spectroscopy (ATMOS) Exper-
iment ATLAS3 measurements made during November
1994. The model used was the AUTOCHEM column
model described by Lary [1996] and Lary et al. [1995,
1996]. The column model was run for 7 days starting
from the ATMOS ATLAS3 vertical profiles of temper-
ature, 03, NO, NO2, N205, HNO3, HNO4, C1ONOa,
H20, CO, CO2, CH4 and NaO. Below 25 km the di-
urnal correction to the NO2 profiles is very important
[Newchurch et al., 1996].
It can be seen from Figure 2 that above 25 km there is
excellent agreement between the model and the observa-
tions in both hemispheres. Below 25 km there is a slight
contrast between the hemispheres. As noted above,
Table 1. Carbon Reduction Reactions Included in
This Study
Reaction 7 used
carbon HNO3 > NO2 2.1 x 10 -2
carbon HNO3 > NO 4.2 x 10 -3
carbon NO2 > NO 2.8 x 10 -2
carbon 03 > 02 1 x 10 -s
the northern hemisphere has a larger soot loading than
the southern hemisphere. The best agreement between
the model simulations and the ATMOS ATLAS3 ob-
servations in the northern hemisphere falls close to the
simulation with 0.2/m2/cm 3. This is in general agree-
ment with the SESAME comparison described above.
In contrast, the best agreement between the model sim-
ulations and the ATMOS ATLAS3 observations in the
southern hemisphere falls close to the simulation with
0.1/m2/cm 3. This is consistent with the fact that the
southern hemisphere has a lower soot loading. Figure 2
also shows how sensitive the HNO3/NOx ratio is to the
soot loading. An increase of the soot loading by a fac-
tor of 10 reduces the HNO3/NOx ratio by a factor of
approximately 100 in the lower stratosphere. Includ-
ing the reduction of HNO3 on soot leads to a simulated
HNOa/NOx ratio within the observed range of the aver-
age free tropospheric ratio of 1-9 reported by Chatfield
[1995].
.... c comparisons not conclusively prove that the
reduction on carbon aerosols actually occurs but they
show that the reduction of NO2 and HNO3 is at least
consistent with observations and can explain the hemi-
spheric assymetry in the observed NO2 and HNOa/NO
ratio vertical profiles. To say this another way, a renox-
ification mechanism, whether it is the one postulated
here or a completely different mechanism, can improve
the agreement between observations and simulations of
the observed NO s partitioning if it is more effective in
the northern hemisphere than the southern hemisphere.
Toumi et al. [1993] considered the ATMOS HNO3/
NO ratio and concluded that the current recommen-
Page 6
3676 LARY ET AL.: CARBON AEROSOLS AND ATMOSPHERIC PHOTOCHEMISTRY
dations for the sulphate N2Os loss are too fast to agree
with observations. Considine et al. [1992], studying
limb infrared monitor of the stratosphere (LIMS) data,
and McElroy et al. [1992] using ATMOS data, also con-
cluded that the current recommendations for the sul-
phate N2Os loss are too fast to agree with observations.
Figure 2 shows that including heterogeneous reduction
of HNO3 on carbon aerosols improves the agreement
between the simulated and observed HNO3/NOx ratio
in the lower stratosphere of the northern hemisphere
by providing a renoxification mechanism. Now that we
have seen that the reduction of HNO3 and NO2 is at
least consistent with observations, the next section ex-
amines in detail the sensitivity of the proposed mech-
anisms to carbon surface area, temperature, altitude,
and day length.
Sensitivity Experiments
To examine the role of HNO3, NOa and 03 reduction
on amorphous carbon aerosols in the lower stratosphere
and the upper troposphere at mid-latitudes a set of ide-
alised model simulations were performed. The numeri-
cal model used for these simulations was AUTOCHEM,
a model described by Lary [1995] and Law et al. [1995,
1996] and Fisher and Lary [1995]. In the simulations a
stationary air parcel at 45øN was considered. The sim-
ulations included the hydrolysis of NaOs, C1ONOa and
BrONOa on sulphate aerosols.
Carbon Surface Area and Temperature
Dependence
In the first set of sensitivity experiments the tem-
perature of an air parcel at 70 mb at equinox was
varied between 200 K and 240 K and the amorphous
carbon aerosol surface area was varied between 0 and
10/m 2 cm -3. For each of these conditions a 7-day sim-
ulation was performed.
Although the observed hemispheric average carbon
aerosol surface area is typically around 1/m acm -3,
much higher areas do exist locally, for example, in air-
craft wakes. In addition, because it is likely that the
carbon aerosol abundance will double over the next 25
years, carbon aerosol areas up to 10/m acm -3 were
considered.
Figure 3 shows that the heterogeneous reduction of
HNO3 on amorphous carbon aerosol is a significant
renoxification process than can obviously continue throug]
out the day. For example, Figure 4 is for midnight.
When no carbon aerosols are present, then the simu-
lation predicts that approximately 80% of NOy is in
the form of HNO3. However, with the assumed 7 val-
ues, increasing the carbon area to just 1 /m acm -3,
a value close to the current hemispheric average, re-
duces the HNO3/NOy ratio to approximately 0.5. Thus
renoxification on carbon aerosols will also be important
in the troposphere and could explain the current dis-
crepancy between observed and modeled values of the
HNOa/NO ratio [Chatfield, 1995]. Figure 3 also shows
that the heterogeneous reduction of NO2 and Os on
amorphous carbon aerosol is quite rapid. The rate of
Os reduction is likely to be faster than that displayed
in Figure 3, as a lower limit 7 value of only 10 -5 has
been used.
Including the heterogeneous reduction of NO2 and
HNOa by amorphous carbon aerosols increases the night-
time NO concentration (Figure 4). Without the hetero-
geneous reduction of NO2 and HNOa models predict an
NO/NOy ratio that is almost zero.
Figure 3 shows that the midnight rate of the heteroge-
neous reduction of NO2 on amorphous carbon aerosol is
a function of both temperature and the amorphous car-
bon aerosol surface area. The rate varies between 10 a
molecules cm -3 s - for an amorphous carbon aerosol
surface area of less than i/m 2 cm -3 and 106 molecules
cm -3 s - for an amorphous carbon aerosol surface area
of 10/m 2 cm -3 at 200 K. Since the midnight rate of
reaction of NO2 with O3 closely follows the rate of re-
duction of NO2 to NO on the amorphous carbon aerosol,
it can be seen from Figures 3 and 4 that the reduction
of NO2 to NO on the amorphous carbon aerosol is the
rate-limiting step of the catalytic ozone loss cycle men-
tioned above.
With a reaction probability for O3 of just 10 -5, at
low carbon aerosol surface areas the direct loss of O3
on the carbon is likely to be faster than the catalytic
loss due to the production of NO (Figure 3). For high
carbon aerosol surface areas the direct loss of O3 on the
carbon is likely to be slower than the catalytic loss due
to the production of NO. By way of a comparison, under
the same conditions, the corresponding ozone loss rate
at noon due to the reaction of HO2 with 03, i.e., the
rate of the major ozone loss cycle, is approximately 105
molecules cm -3 s - at 200 K, rising to 106 molecules
cm -3 s - at 240 K. An ozone loss rate that can reach
106 molecules cm -3 s - is therefore clearly asignificant
ozone loss rate.
Figure 3 shows that the midnight rate of the het-
erogeneous reduction of HNO3 on amorphous carbon
aerosol is a function of both temperature and the amor-
phous carbon aerosol surface area. The rate varies be-
tween 3 x 103 molecules cm -3 s - for an amorphous
carbon aerosol surface area of less than i /m 2 cm -3
up to 8 x 103 molecules cm -3 s - for an amorphous
carbon aerosol surface area of 10/m 2 cm -3 at 240 K.
This renoxification by the reduction of HNO3 provides
additional NOs which can take part in the catalytic
destruction of ozone.
Figure 4 shows that the additional ozone loss caused
by the heterogeneous reduction of HNO3, NO2 and O3
on amorphous carbon aerosol over the 7-day simulation
period reaches nearly 3% (80 ppbv) for an amorphous
carbon aerosol surface area of 10 um 2 cm -3. It is note-
worthy that the additional ozone loss caused by the het-
erogeneous reduction of NOu is almost independent of
temperature if the 7 value is not temperature depen-
dations for the sulphate N2Os loss are too fast to agree
with observations. Considine et al. [1992], studying
limb infrared monitor of the stratosphere (LIMS) data,
and McElroy et al. [1992] using ATMOS data, also con-
cluded that the current recommendations for the sul-
phate N2Os loss are too fast to agree with observations.
Figure 2 shows that including heterogeneous reduction
of HNO3 on carbon aerosols improves the agreement
between the simulated and observed HNO3/NOx ratio
in the lower stratosphere of the northern hemisphere
by providing a renoxification mechanism. Now that we
have seen that the reduction of HNO3 and NO2 is at
least consistent with observations, the next section ex-
amines in detail the sensitivity of the proposed mech-
anisms to carbon surface area, temperature, altitude,
and day length.
Sensitivity Experiments
To examine the role of HNO3, NOa and 03 reduction
on amorphous carbon aerosols in the lower stratosphere
and the upper troposphere at mid-latitudes a set of ide-
alised model simulations were performed. The numeri-
cal model used for these simulations was AUTOCHEM,
a model described by Lary [1995] and Law et al. [1995,
1996] and Fisher and Lary [1995]. In the simulations a
stationary air parcel at 45øN was considered. The sim-
ulations included the hydrolysis of NaOs, C1ONOa and
BrONOa on sulphate aerosols.
Carbon Surface Area and Temperature
Dependence
In the first set of sensitivity experiments the tem-
perature of an air parcel at 70 mb at equinox was
varied between 200 K and 240 K and the amorphous
carbon aerosol surface area was varied between 0 and
10/m 2 cm -3. For each of these conditions a 7-day sim-
ulation was performed.
Although the observed hemispheric average carbon
aerosol surface area is typically around 1/m acm -3,
much higher areas do exist locally, for example, in air-
craft wakes. In addition, because it is likely that the
carbon aerosol abundance will double over the next 25
years, carbon aerosol areas up to 10/m acm -3 were
considered.
Figure 3 shows that the heterogeneous reduction of
HNO3 on amorphous carbon aerosol is a significant
renoxification process than can obviously continue throug]
out the day. For example, Figure 4 is for midnight.
When no carbon aerosols are present, then the simu-
lation predicts that approximately 80% of NOy is in
the form of HNO3. However, with the assumed 7 val-
ues, increasing the carbon area to just 1 /m acm -3,
a value close to the current hemispheric average, re-
duces the HNO3/NOy ratio to approximately 0.5. Thus
renoxification on carbon aerosols will also be important
in the troposphere and could explain the current dis-
crepancy between observed and modeled values of the
HNOa/NO ratio [Chatfield, 1995]. Figure 3 also shows
that the heterogeneous reduction of NO2 and Os on
amorphous carbon aerosol is quite rapid. The rate of
Os reduction is likely to be faster than that displayed
in Figure 3, as a lower limit 7 value of only 10 -5 has
been used.
Including the heterogeneous reduction of NO2 and
HNOa by amorphous carbon aerosols increases the night-
time NO concentration (Figure 4). Without the hetero-
geneous reduction of NO2 and HNOa models predict an
NO/NOy ratio that is almost zero.
Figure 3 shows that the midnight rate of the heteroge-
neous reduction of NO2 on amorphous carbon aerosol is
a function of both temperature and the amorphous car-
bon aerosol surface area. The rate varies between 10 a
molecules cm -3 s - for an amorphous carbon aerosol
surface area of less than i/m 2 cm -3 and 106 molecules
cm -3 s - for an amorphous carbon aerosol surface area
of 10/m 2 cm -3 at 200 K. Since the midnight rate of
reaction of NO2 with O3 closely follows the rate of re-
duction of NO2 to NO on the amorphous carbon aerosol,
it can be seen from Figures 3 and 4 that the reduction
of NO2 to NO on the amorphous carbon aerosol is the
rate-limiting step of the catalytic ozone loss cycle men-
tioned above.
With a reaction probability for O3 of just 10 -5, at
low carbon aerosol surface areas the direct loss of O3
on the carbon is likely to be faster than the catalytic
loss due to the production of NO (Figure 3). For high
carbon aerosol surface areas the direct loss of O3 on the
carbon is likely to be slower than the catalytic loss due
to the production of NO. By way of a comparison, under
the same conditions, the corresponding ozone loss rate
at noon due to the reaction of HO2 with 03, i.e., the
rate of the major ozone loss cycle, is approximately 105
molecules cm -3 s - at 200 K, rising to 106 molecules
cm -3 s - at 240 K. An ozone loss rate that can reach
106 molecules cm -3 s - is therefore clearly asignificant
ozone loss rate.
Figure 3 shows that the midnight rate of the het-
erogeneous reduction of HNO3 on amorphous carbon
aerosol is a function of both temperature and the amor-
phous carbon aerosol surface area. The rate varies be-
tween 3 x 103 molecules cm -3 s - for an amorphous
carbon aerosol surface area of less than i /m 2 cm -3
up to 8 x 103 molecules cm -3 s - for an amorphous
carbon aerosol surface area of 10/m 2 cm -3 at 240 K.
This renoxification by the reduction of HNO3 provides
additional NOs which can take part in the catalytic
destruction of ozone.
Figure 4 shows that the additional ozone loss caused
by the heterogeneous reduction of HNO3, NO2 and O3
on amorphous carbon aerosol over the 7-day simulation
period reaches nearly 3% (80 ppbv) for an amorphous
carbon aerosol surface area of 10 um 2 cm -3. It is note-
worthy that the additional ozone loss caused by the het-
erogeneous reduction of NOu is almost independent of
temperature if the 7 value is not temperature depen-
Page 7
LARY ET AL.: CARBON AEROSOLS AND ATMOSPHERIC PHOTOCHEMISTRY 3677
Midnight rate of
HNO --)
0 I 2 3 4 5 6 7 8 9 10
240 L i___ l . I .j...I !. I... ..... I ..t.. I...t .... I.. _ [..
'-':.. :.-:,... :.-': : ;,.' ..... , : :-..:...,..-....-......:. . . . ................................................
f ::;::':½::;'::::::'':'R\"\v' ............... =============================================================================================== ::.<::' ...'::.'. . =:-:-.-.--__--_-:___-_:. .-..-.----------------.-.-.--..-........;:.: 220 i1t'
i::.,.'. :':':' : '\"\"- - -. :.i a '-<':' ..................... \"--\"--' '\"'\"' \"\"-'-':'-'-'-'-'-\" I - 'J:..'f _ \" . . . .:,;;:- --.---
200
0 I 2 3 4 5 6 7 8 9 10
Carbon Aerosol Surface Area
38928 :' :' \"' \"'::': !..'::;ii:
35795 \"'\"'\"\"\"':'\"'J!?
28255
26035
24598
21427
15287
Midnight rate of
H --) NO
o I 2 3 4 5 6 7 8 9 o
240 I
*:-:. -'... j:?,'x-: :':':':... :.....:.:.:j:.:.:: :
;::-'::\":..-...:. _ .::::;\"'\"':.:..:. . '\"'\":\"\" :..' :::i:::'
'- '\"\"' '\"\"\"'\"\"'''\" ' \ ':\ : ' ' <\":- -'.:.-d :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: \"'\"' :<\"' \" :\"' \"\":<:: ...... - '\"\"\"'\" '\ '\"\"'\"' =============================================================
......... :, . :': ........................................ :\" \" : \"- - ---':i:;
220
210
IJiJJJJJ ................. ':\"::::''\"' 200
0 I 2 3 4 5 6 7 8 g 10
Carbon Aerosol Surface Area
5651 ..... ,,::.:.:.,+:: 5207 , -'. -.. ;i
4919 :<\"½'' ' '\":' '' '\"
4285 '\"\" \":'\"'\":\"iiii
3057 '\"\"':\"<<'\"\" :'\"::
Midnight rate of
-> NO
0 I 2 3 4 5 6
....'-;-'-.__.._ :.... :_-:-:-:_-.s.\"-'---'-'--- ' ' '.:.. '::::'...:.-:::< . :.%4.4.-:.:.<:,-: :,-.: :=.
--..-....-.._._. .......,,,.... .-,<--.
230- -----'-----'--\"---\"---\"\"'''\"'; ,\". -
.................. *'\"'-:'::::-::'?-.:,< ,e..-.-'-
................................
'- .:.:.-.. :.x, ;:.:.:.:.:.:.:-:.'
l::: ........... ,,,,,,,<:,,., ,...;..<..,::
.,: ,.-..: ,.:, ...............
.................. :\":'*'' \"'- ß . ß ':\"-i :-'-':..::-'-'.-:::' .. ..
. :.-
200 V\"': ....... i ..... :'\"\":i-':'\";' ..... :-\"r'W'm' ..... i' .... ,' 'i \",
0 I 2 3 4 5 6
7 8 g 10
ß ' ....
::::::::::::::::::::::
7 8 9 10
Carbon Aerosol Surface Area
o
240 -
.. 230-
v
.....
200326 \"!i'i'i'!!: ?:i!: ' '
153506 ..-.... .':. :. , - : -:...-. ::'. :::: 220
126362 '\"\"';'\" ' -\" ;'':!}!
''\" E
78179 ,,... - .,-<,,....,: ß
57395 \"\":: i\"\"\"
. ::.. mo- 37138 '\"'-\".., .. ß '-:'.:
200
Midnight rate of
I 2 3 4 5 6 7 8 g 10
-'.'-'--..... '. . ::-\" ..,,,<....,.%..,.'..-..-.,.,,,.-..:,.-..:::-....:.-.- :<-:<--: . ,s::-::::-:: .... - 'I J['\"'\"'\"'\"'\"\"'\":':::::.. :iii .... \":\" ' < :JJ' :\ :':\"\":'.. !::...:'::::i?:::.: ..
:\" '\" \"'\"\" :'::ii :::::::::::::::::::::::::::::::::
.... .... : ::::..:::::..:--<......,..-.:::::........::,. ,, -: - .--, .':. - .'.-. '- . .< ..... ::.. -: -: . - ................ ..... .............. - ..... .::...::.::::: ::- :....: ... ß . : . :::::::: :: ::: ::::::: :::::
'\":'::- : ::::-:,,, :::. -<.::::'::: ,:,..'.:....: ,,,, G,,-, ,,,. :::.:...:.:..:.. :.::, ::: ,-.., :.. .:::..: .. 55256 ......
JV ::. .::::.::: g : ...........:.:.:.::: ., . :5 :::! o,: ' ,! g \"'\"' <;::::' :' f 48753 ::::.:.....-::::::: - --':. : <.... .' :: ,,.. e. .-..\":....'.: o, o, -:-:,. :-- ::..-::: , :: ....... --,,, : ... : . : -: --: .:..' .. -.:.::': ?--. ': .'.:<.:.: . , . : .. ..'- \"... -.e..:? : :: .: ',,': : 2347 '\"' ':\"i. ::::::::::::::::::::::::-:::i::. 36038
........................... ..... - --.: -:: .::::::..-::: ..... :: ,-
.:::::::::.:. .[- \"',. :
........... ' '\"' ''\"'...........- -.. -.. ' .\":-: :\"\":'\"\"\"' \"'\"'\"' '\"'\ ::* .......... \"\"\" :'<<'\" . i:
.... ::::;:::.::::.. : 23698'\"'\":'½:--:,.........}i
:..,,.., :.. ,..:,:..... :,.. : :: , ::::..: ,.,, :.. , : -...:.:: '.,,:\"' .: : ...: .:: .:,, ..:.: .......-.......:: : :: :,:
11692
\"-'\"\"'\"'\"'\"\"\" ':\"::iii \"..:-',.._ _ ,'.-'.-\"\" ......ltl''\ \ ': ':'\"- . - ß ß 1: i-
f I [ I [ I i I i I I I [ I [ I ]
0 I 2 3 4 5 6 7 8 9 10
Carbon Aerosol Surface Area
Figure 3. Results for midnight at the end of a set of 7-day simulations. During the 7-day
simulations the air parcel was kept at 70 mb, 45øN at equinox. The temperature and amorphous
carbon aerosol surface area present were kept constant for each air parcel through out the 7-day
period. The results are plotted as a function of temperature. (in Kelvin) and the amorphous
carbon aerosol surface area in pm cm -a. Note that each plot has a different contour interval.
dent. This is in contrast, for example, to the hydrolysis
of N20.s where although the 7 value is only weakly tem-
perature dependent, the N205 concentration is strongly
temperature dependent. For amorphous carbon aerosol
surface areas that are close to the hemispheric average,
the additional ozone loss is of the order of 0.3-0.5% over
the period of the 1-week simulation.
Figure 4 shows that the nighttime ozone loss due
to the heterogeneous reduction of HNO3 and NO has
substantially reduced the nighttime ozone lifetime from
around 350 months without reduction on carbon to just
52 months with a carbon area of only 1 Fm 2 cm -3.
Heterogeneous reduction of HNO3, NO2 and 03 there-
fore represents a potentially important in situ ozone loss
mechanism which can operate throughout the day at
all latitudes in the lower stratosphere and upper tropo-
sphere, irrespective of the temperature, and it is likely
that it contributes to the observed ozone trends. This
mechanism will increase in importance with the increase
in the abundance of carbon aerosol. It is therefore a
mechanism that must be accounted for when consider-
ing the impact of increased air transport and all com-
bustion processes on the atmosphere.
Altitude Dependence
In the second set of sensitivity experiments the alti-
tude of the air parcel was varied between 10 and 25 km.
Figure 5 shows the additional 03 loss caused by includ-
ing the heterogeneous reduction of HNO3 and NO2 on
amorphous carbon aerosol as a function of altitude and
carbon aerosol surface area. It is immediately apparent
that in the stratosphere the enhanced levels of NOx lead
Midnight rate of
HNO --)
0 I 2 3 4 5 6 7 8 9 10
240 L i___ l . I .j...I !. I... ..... I ..t.. I...t .... I.. _ [..
'-':.. :.-:,... :.-': : ;,.' ..... , : :-..:...,..-....-......:. . . . ................................................
f ::;::':½::;'::::::'':'R\"\v' ............... =============================================================================================== ::.<::' ...'::.'. . =:-:-.-.--__--_-:___-_:. .-..-.----------------.-.-.--..-........;:.: 220 i1t'
i::.,.'. :':':' : '\"\"- - -. :.i a '-<':' ..................... \"--\"--' '\"'\"' \"\"-'-':'-'-'-'-'-\" I - 'J:..'f _ \" . . . .:,;;:- --.---
200
0 I 2 3 4 5 6 7 8 9 10
Carbon Aerosol Surface Area
38928 :' :' \"' \"'::': !..'::;ii:
35795 \"'\"'\"\"\"':'\"'J!?
28255
26035
24598
21427
15287
Midnight rate of
H --) NO
o I 2 3 4 5 6 7 8 9 o
240 I
*:-:. -'... j:?,'x-: :':':':... :.....:.:.:j:.:.:: :
;::-'::\":..-...:. _ .::::;\"'\"':.:..:. . '\"'\":\"\" :..' :::i:::'
'- '\"\"' '\"\"\"'\"\"'''\" ' \ ':\ : ' ' <\":- -'.:.-d :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: \"'\"' :<\"' \" :\"' \"\":<:: ...... - '\"\"\"'\" '\ '\"\"'\"' =============================================================
......... :, . :': ........................................ :\" \" : \"- - ---':i:;
220
210
IJiJJJJJ ................. ':\"::::''\"' 200
0 I 2 3 4 5 6 7 8 g 10
Carbon Aerosol Surface Area
5651 ..... ,,::.:.:.,+:: 5207 , -'. -.. ;i
4919 :<\"½'' ' '\":' '' '\"
4285 '\"\" \":'\"'\":\"iiii
3057 '\"\"':\"<<'\"\" :'\"::
Midnight rate of
-> NO
0 I 2 3 4 5 6
....'-;-'-.__.._ :.... :_-:-:-:_-.s.\"-'---'-'--- ' ' '.:.. '::::'...:.-:::< . :.%4.4.-:.:.<:,-: :,-.: :=.
--..-....-.._._. .......,,,.... .-,<--.
230- -----'-----'--\"---\"---\"\"'''\"'; ,\". -
.................. *'\"'-:'::::-::'?-.:,< ,e..-.-'-
................................
'- .:.:.-.. :.x, ;:.:.:.:.:.:.:-:.'
l::: ........... ,,,,,,,<:,,., ,...;..<..,::
.,: ,.-..: ,.:, ...............
.................. :\":'*'' \"'- ß . ß ':\"-i :-'-':..::-'-'.-:::' .. ..
. :.-
200 V\"': ....... i ..... :'\"\":i-':'\";' ..... :-\"r'W'm' ..... i' .... ,' 'i \",
0 I 2 3 4 5 6
7 8 g 10
ß ' ....
::::::::::::::::::::::
7 8 9 10
Carbon Aerosol Surface Area
o
240 -
.. 230-
v
.....
200326 \"!i'i'i'!!: ?:i!: ' '
153506 ..-.... .':. :. , - : -:...-. ::'. :::: 220
126362 '\"\"';'\" ' -\" ;'':!}!
''\" E
78179 ,,... - .,-<,,....,: ß
57395 \"\":: i\"\"\"
. ::.. mo- 37138 '\"'-\".., .. ß '-:'.:
200
Midnight rate of
I 2 3 4 5 6 7 8 g 10
-'.'-'--..... '. . ::-\" ..,,,<....,.%..,.'..-..-.,.,,,.-..:,.-..:::-....:.-.- :<-:<--: . ,s::-::::-:: .... - 'I J['\"'\"'\"'\"'\"\"'\":':::::.. :iii .... \":\" ' < :JJ' :\ :':\"\":'.. !::...:'::::i?:::.: ..
:\" '\" \"'\"\" :'::ii :::::::::::::::::::::::::::::::::
.... .... : ::::..:::::..:--<......,..-.:::::........::,. ,, -: - .--, .':. - .'.-. '- . .< ..... ::.. -: -: . - ................ ..... .............. - ..... .::...::.::::: ::- :....: ... ß . : . :::::::: :: ::: ::::::: :::::
'\":'::- : ::::-:,,, :::. -<.::::'::: ,:,..'.:....: ,,,, G,,-, ,,,. :::.:...:.:..:.. :.::, ::: ,-.., :.. .:::..: .. 55256 ......
JV ::. .::::.::: g : ...........:.:.:.::: ., . :5 :::! o,: ' ,! g \"'\"' <;::::' :' f 48753 ::::.:.....-::::::: - --':. : <.... .' :: ,,.. e. .-..\":....'.: o, o, -:-:,. :-- ::..-::: , :: ....... --,,, : ... : . : -: --: .:..' .. -.:.::': ?--. ': .'.:<.:.: . , . : .. ..'- \"... -.e..:? : :: .: ',,': : 2347 '\"' ':\"i. ::::::::::::::::::::::::-:::i::. 36038
........................... ..... - --.: -:: .::::::..-::: ..... :: ,-
.:::::::::.:. .[- \"',. :
........... ' '\"' ''\"'...........- -.. -.. ' .\":-: :\"\":'\"\"\"' \"'\"'\"' '\"'\ ::* .......... \"\"\" :'<<'\" . i:
.... ::::;:::.::::.. : 23698'\"'\":'½:--:,.........}i
:..,,.., :.. ,..:,:..... :,.. : :: , ::::..: ,.,, :.. , : -...:.:: '.,,:\"' .: : ...: .:: .:,, ..:.: .......-.......:: : :: :,:
11692
\"-'\"\"'\"'\"'\"\"\" ':\"::iii \"..:-',.._ _ ,'.-'.-\"\" ......ltl''\ \ ': ':'\"- . - ß ß 1: i-
f I [ I [ I i I i I I I [ I [ I ]
0 I 2 3 4 5 6 7 8 9 10
Carbon Aerosol Surface Area
Figure 3. Results for midnight at the end of a set of 7-day simulations. During the 7-day
simulations the air parcel was kept at 70 mb, 45øN at equinox. The temperature and amorphous
carbon aerosol surface area present were kept constant for each air parcel through out the 7-day
period. The results are plotted as a function of temperature. (in Kelvin) and the amorphous
carbon aerosol surface area in pm cm -a. Note that each plot has a different contour interval.
dent. This is in contrast, for example, to the hydrolysis
of N20.s where although the 7 value is only weakly tem-
perature dependent, the N205 concentration is strongly
temperature dependent. For amorphous carbon aerosol
surface areas that are close to the hemispheric average,
the additional ozone loss is of the order of 0.3-0.5% over
the period of the 1-week simulation.
Figure 4 shows that the nighttime ozone loss due
to the heterogeneous reduction of HNO3 and NO has
substantially reduced the nighttime ozone lifetime from
around 350 months without reduction on carbon to just
52 months with a carbon area of only 1 Fm 2 cm -3.
Heterogeneous reduction of HNO3, NO2 and 03 there-
fore represents a potentially important in situ ozone loss
mechanism which can operate throughout the day at
all latitudes in the lower stratosphere and upper tropo-
sphere, irrespective of the temperature, and it is likely
that it contributes to the observed ozone trends. This
mechanism will increase in importance with the increase
in the abundance of carbon aerosol. It is therefore a
mechanism that must be accounted for when consider-
ing the impact of increased air transport and all com-
bustion processes on the atmosphere.
Altitude Dependence
In the second set of sensitivity experiments the alti-
tude of the air parcel was varied between 10 and 25 km.
Figure 5 shows the additional 03 loss caused by includ-
ing the heterogeneous reduction of HNO3 and NO2 on
amorphous carbon aerosol as a function of altitude and
carbon aerosol surface area. It is immediately apparent
that in the stratosphere the enhanced levels of NOx lead
Page 8
3678 LARY ET AL.: CARBON AEROSOLS AND ATMOSPHERIC PHOTOCHEMISTRY
Midnight rate of
NO + O --) NO + O
0 I 2 3 4 5 6 7 8 9 10
240 I ' i I. I I J J
---...:-:-:-:.,--.-:::::::::: ....... -. x, .'\"'---',
230 \"'\"' '-\"'\"':' \"\"'\"' \" ß ' '\"- :'-\"\"\"-:\"\"'\"' -,,',, :., .-- .--x,,x,-,,--,- -'.-- ...'-:.,...-,**;<. *::._-..-_::_
.......................... :-- -- N - - '\" '\"'\" \"': \"'i ,.c<;...-<..-..-.:..-<.--cc:- . ..... -.:.c:.-.::.::¾ . :::::';:-'.':-*, : :..-.:.:.:.:,- <:&':.::.::: .A,:, , ,,, 13i88 102822 ............. '\":
'84783
.......................... \"
'\"'\"\"'\"'\" ß \"\"': - ß -- ß -\". -- '-.. ,, ' '\ ''\" ' '\"'\"\" '\ \ \ ''- \"'\"\":': -.-:it- ....
...................... ''\" ' \"'!i
' 7959
_yu I ' I ' I ' I I I . I I ' I I I
0 I 2 3 4 5 6 7 8 9 10
Carbon Aerosol Surface Area
Midnight
HNOJNO
0 I 2 3 4 5 6 7 8 9 10
,..I .,...J . [.. ..[. ]. ... !.... 1 .....
230-:::::::::::::::::::::::::::::::::::::::::::::::::
v
, 220-
E :--:-: ..:.:-:.:---:. :-:-. -..-:.: :.:.: ,.-.....:....- - : : --:.:.:c.:.:.:-:.-:..-<½.:..:A:- ß :::::::::::::::::::::::::::::: I-- 210-' ............... :-' -:-'.- :' .................. :':\"'':: - i \"
200
0 1 2 3 4 5 6 7 8 9 10
Carbon Aerosol Surface Area
0.511 --'-'-:---'\"-- ' .ii
0.421 '\" ';':' \" :\" '::-- -:' 0.339
0.245 0.221
0.195 '\"\"(. '
0.147
o. 128
240
,.-, 230-
v
t 22o-
I-- 210-
_
200 !
0
Midnight
NOJNO,
0 I 2 3 4 5 6 7 8 9 10
J,...:.:.:...:.:.:...!i....,....:.:....:.....:.... ; l.: : i! i . .. J . , .L ,J: . .L,,J..,,.-.. .. .
......... ,,.-------------- ,, ...,,, .......,:. , ,, ,-
......... %N'\"\"l,, 'x---- ':-:'.:..:.!,,:-;.':'½:' '\" ' ' \"\"- ''- -' - \ :; . ..... \"'\"' ''\"'
._ ........... ; .. ,,- -< -,,,: :,, ,
.,...::,-..-. r ...,-' ..........
L .......... \"'\"\"'\"\"'\"\"'\"'\"''':-,,,, '-';'..- .-..-..:..:ii:::::: ...:.::::%¾:.?'!::::?:?.:::.::i:.i:.i:::.:.?:i !--'\" \"\ \"' '%'\" "'' \ '' '\":':--' '- ,. -:::'\"::.::i:'-?-'\":.;!::::??. ½
....--.....,.... .... . .......... .:j.:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
\"\"\"'\"'\"'\"' ''\" '-''\" \"'\"'\"'\" '\" '\" ':'''\"\"'\" :'\"\" ':: :': : ' :: i \" ': '':'i \"::: ' ,' -\":'; '' :'½
I 2 3 4 5 6 7 8 9 10
Carbon Aerosol Surface Area
0.657
,;.. :-:-:.:.... y:. :::::::::
0.491 ..........
0.446 ....................
0.372 \"\"i !ii :'-' 0.333 A
0.304 . ,,,.x.. 0.272 '\"\"- <.....:'J:
0.219 '\"' \":*::\" ' ' \"-.'{i
0.162 \"'\"\"' ':' '\"\"' ' \"\":\":
Midnight
NO/NO
_
....................... : .,-.....::::::,: ,; ........... ,:, ,. ,. ,..... ,.......... ,.
230
,,, ................ ,,,,,,::...,! .....,,. ,, ,.. ::..:,.
............ .. ' ,: ,, ':-'i ..- .\":
'\" 220 __ \"' ;\", ..'.::.- .':;, ' 4.50 E_ 04 '\"\"-: :-:-......-. -:;;;i
_ :-'-'...-'.;;: - -'.:'i,':' '\"\" \"% ....... - ' '\"'\"'\"\"'\"%' \"' '\ '\ ':\"--' - -'- - - :'- - -- :.:i:i
E ,.:----,,,,r ß , -\",% :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: 2.58E-04 . . ..:.... i!i.
I-. ,,.,., ,.,... .................. ':\" \":\" \"\" ':' -: .' /,::i;:!:iiiiiii:ii::!:;;!!!:!i!ii!i!i:i!::i:i::i::::!:::::i!iii:i!i::iiiii!i::::i: 1.43E-04
- ................ .. ......,, .... -.-..-,,,_____-....::........ ===========================================================================================================
::,oo - ................ \"' '%11\"'\"\"\"\"'' .``: ;i!::: ;:::::::i:::::.:.::::; ......... : ;:-;:.-:-:.-
0 I 2 3 4 5 6 7 8 9 10
Carbon Aerosol Surface Area
0 I 2 3 4 5 6 7 8 9 10
Carbon Aerosol Surface Area
...-.....-.-.-.-.-.-.._-.
842.6' '\":\" '\ ' :::' ' ::\"ii 595.2 ::::::: .................
========================
471.1 \"-'?¾<.
391.8 ?, 333.9
259.9 \"'\":'\"':'\"- ' :-.-- ' 233.2
Additional Ozone loss (%)
due to reactions on carbon
0 I 2 3 4 5 6 7 8 9 10
I ß ' ' 240 ................... ....,,,.....:,;:,,%
.......... ¾: :, ,,..... ,x,, !!!i;:!?i?:::..-::. : ::::::::::::::::::::::::::::::::
:::::! .... :-::>..',\"'\"\"\"'-'\" ' '\"'\ '\ '\ '....',.. :. x :.:;:;:::; 2.74 :::::::::::::::::::::::::::::::::::::::: :::::' % '\"-;--- ';;-'- .' ::::::::. \" -. :,. . .':.:.'. <$ - -... ,,:,:.-, ........... 2.48 ==================================
..... -.,. ;-----..-,----,-.... :..--.- . .. ......... :.: , -,:' ' -.:.:..-.:.:.:*'-'::::-\"-':-'. .... :::.:!i:: &,.. =============================================== .........................
-:,;- % , ß :4..-.::..:.:44.''\"---\"-'-'-'-'-'-'-'- -'--'-:.:.... -,:.-::::.'.-: :,: : :\":.,:':-'\".',.-, '--------------\"-\"-'
.......................... ;:s :: -'.::::,,.'.:::::: \" ... . ........ :::7.\".'.-.'.'.'.'.'.'.'.'.'.'.'. 2.32
::::-. ,-.i':-,\". \"t' ..i:i:i:i:ii::!::..--- - .,:..'.:.,--.-:; :.:;-i:i:i:i:i:!:i:-:!:!:!:!:i:i '':: -'-:: - - -' - -:-.----.'\"i:.il ':::\"-.\"'.\"\": \"' '''\ '\ ''* ::':':'::':'\"::: .... :\"'\"'\"\"?',,i ! ;?,',ii?,i!!! 2.5':'\"\"\"'\"\"-\"'- -?-::-:.-: i::i, '\" : ........................ - .......
................. -,, . ,_ ,:::! ....... . ........................................... .............
,., ........ -: -,:,:.::.-.:.:,.-,- ;:,-,.. . ....... , :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: 1.94 220 - x -. ...... ,,, .... , .... ?,.-:,, ,,; .... .......................
:,,-...'.-o-;.:j.;.-ii.:'::,.!½',i'.,.,-,-'.:11;ii:- =============================================================== .73:,'\"'.' ...... ..
:: ,,, .............. ....,....:::\iiiii::::ill .. :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
-\"- ............... ' '' ','\",,:iiiii:::iiiiiiii-. \":::-':\"':':-':-'::::::':::::';::'::::'::'::'::' ':';;:; .........
.:.:.:.:.:. :: :::::::::::::::::::::::::::: . ..: . . :_ _ . 0. :::::::::::::::::::::
0 I 2 3 4 5 6 7 8 9 10
Carbon Aerosol Surface Area
Figure 4. Additional results for midnight at the end of a set of 7-day simulations. During the
seven day simulations the air parcel was kept at 70 rob, 45øN at equinox. The temperature and
amorphous carbon aerosol surface area present were kept constant for each air parcel through
out the 7-day period. The results are plotted as a function of temperature (in Kelvin) and
the amorphous carbon aerosol surface area in m cm -3. Note that each plot has a different
contour interval. The NO/NO, NO/NO and HNO3/NO ratios are dimensionless. The 03
loss time-scale at midnight is in units of days. The additional 03 loss caused by including the
heterogeneous reactions on amorphous carbon aerosol over the 7 day simulation period is shown
as a percentage.
Midnight rate of
NO + O --) NO + O
0 I 2 3 4 5 6 7 8 9 10
240 I ' i I. I I J J
---...:-:-:-:.,--.-:::::::::: ....... -. x, .'\"'---',
230 \"'\"' '-\"'\"':' \"\"'\"' \" ß ' '\"- :'-\"\"\"-:\"\"'\"' -,,',, :., .-- .--x,,x,-,,--,- -'.-- ...'-:.,...-,**;<. *::._-..-_::_
.......................... :-- -- N - - '\" '\"'\" \"': \"'i ,.c<;...-<..-..-.:..-<.--cc:- . ..... -.:.c:.-.::.::¾ . :::::';:-'.':-*, : :..-.:.:.:.:,- <:&':.::.::: .A,:, , ,,, 13i88 102822 ............. '\":
'84783
.......................... \"
'\"'\"\"'\"'\" ß \"\"': - ß -- ß -\". -- '-.. ,, ' '\ ''\" ' '\"'\"\" '\ \ \ ''- \"'\"\":': -.-:it- ....
...................... ''\" ' \"'!i
' 7959
_yu I ' I ' I ' I I I . I I ' I I I
0 I 2 3 4 5 6 7 8 9 10
Carbon Aerosol Surface Area
Midnight
HNOJNO
0 I 2 3 4 5 6 7 8 9 10
,..I .,...J . [.. ..[. ]. ... !.... 1 .....
230-:::::::::::::::::::::::::::::::::::::::::::::::::
v
, 220-
E :--:-: ..:.:-:.:---:. :-:-. -..-:.: :.:.: ,.-.....:....- - : : --:.:.:c.:.:.:-:.-:..-<½.:..:A:- ß :::::::::::::::::::::::::::::: I-- 210-' ............... :-' -:-'.- :' .................. :':\"'':: - i \"
200
0 1 2 3 4 5 6 7 8 9 10
Carbon Aerosol Surface Area
0.511 --'-'-:---'\"-- ' .ii
0.421 '\" ';':' \" :\" '::-- -:' 0.339
0.245 0.221
0.195 '\"\"(. '
0.147
o. 128
240
,.-, 230-
v
t 22o-
I-- 210-
_
200 !
0
Midnight
NOJNO,
0 I 2 3 4 5 6 7 8 9 10
J,...:.:.:...:.:.:...!i....,....:.:....:.....:.... ; l.: : i! i . .. J . , .L ,J: . .L,,J..,,.-.. .. .
......... ,,.-------------- ,, ...,,, .......,:. , ,, ,-
......... %N'\"\"l,, 'x---- ':-:'.:..:.!,,:-;.':'½:' '\" ' ' \"\"- ''- -' - \ :; . ..... \"'\"' ''\"'
._ ........... ; .. ,,- -< -,,,: :,, ,
.,...::,-..-. r ...,-' ..........
L .......... \"'\"\"'\"\"'\"\"'\"'\"''':-,,,, '-';'..- .-..-..:..:ii:::::: ...:.::::%¾:.?'!::::?:?.:::.::i:.i:.i:::.:.?:i !--'\" \"\ \"' '%'\" "'' \ '' '\":':--' '- ,. -:::'\"::.::i:'-?-'\":.;!::::??. ½
....--.....,.... .... . .......... .:j.:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
\"\"\"'\"'\"'\"' ''\" '-''\" \"'\"'\"'\" '\" '\" ':'''\"\"'\" :'\"\" ':: :': : ' :: i \" ': '':'i \"::: ' ,' -\":'; '' :'½
I 2 3 4 5 6 7 8 9 10
Carbon Aerosol Surface Area
0.657
,;.. :-:-:.:.... y:. :::::::::
0.491 ..........
0.446 ....................
0.372 \"\"i !ii :'-' 0.333 A
0.304 . ,,,.x.. 0.272 '\"\"- <.....:'J:
0.219 '\"' \":*::\" ' ' \"-.'{i
0.162 \"'\"\"' ':' '\"\"' ' \"\":\":
Midnight
NO/NO
_
....................... : .,-.....::::::,: ,; ........... ,:, ,. ,. ,..... ,.......... ,.
230
,,, ................ ,,,,,,::...,! .....,,. ,, ,.. ::..:,.
............ .. ' ,: ,, ':-'i ..- .\":
'\" 220 __ \"' ;\", ..'.::.- .':;, ' 4.50 E_ 04 '\"\"-: :-:-......-. -:;;;i
_ :-'-'...-'.;;: - -'.:'i,':' '\"\" \"% ....... - ' '\"'\"'\"\"'\"%' \"' '\ '\ ':\"--' - -'- - - :'- - -- :.:i:i
E ,.:----,,,,r ß , -\",% :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: 2.58E-04 . . ..:.... i!i.
I-. ,,.,., ,.,... .................. ':\" \":\" \"\" ':' -: .' /,::i;:!:iiiiiii:ii::!:;;!!!:!i!ii!i!i:i!::i:i::i::::!:::::i!iii:i!i::iiiii!i::::i: 1.43E-04
- ................ .. ......,, .... -.-..-,,,_____-....::........ ===========================================================================================================
::,oo - ................ \"' '%11\"'\"\"\"\"'' .``: ;i!::: ;:::::::i:::::.:.::::; ......... : ;:-;:.-:-:.-
0 I 2 3 4 5 6 7 8 9 10
Carbon Aerosol Surface Area
0 I 2 3 4 5 6 7 8 9 10
Carbon Aerosol Surface Area
...-.....-.-.-.-.-.-.._-.
842.6' '\":\" '\ ' :::' ' ::\"ii 595.2 ::::::: .................
========================
471.1 \"-'?¾<.
391.8 ?, 333.9
259.9 \"'\":'\"':'\"- ' :-.-- ' 233.2
Additional Ozone loss (%)
due to reactions on carbon
0 I 2 3 4 5 6 7 8 9 10
I ß ' ' 240 ................... ....,,,.....:,;:,,%
.......... ¾: :, ,,..... ,x,, !!!i;:!?i?:::..-::. : ::::::::::::::::::::::::::::::::
:::::! .... :-::>..',\"'\"\"\"'-'\" ' '\"'\ '\ '\ '....',.. :. x :.:;:;:::; 2.74 :::::::::::::::::::::::::::::::::::::::: :::::' % '\"-;--- ';;-'- .' ::::::::. \" -. :,. . .':.:.'. <$ - -... ,,:,:.-, ........... 2.48 ==================================
..... -.,. ;-----..-,----,-.... :..--.- . .. ......... :.: , -,:' ' -.:.:..-.:.:.:*'-'::::-\"-':-'. .... :::.:!i:: &,.. =============================================== .........................
-:,;- % , ß :4..-.::..:.:44.''\"---\"-'-'-'-'-'-'-'- -'--'-:.:.... -,:.-::::.'.-: :,: : :\":.,:':-'\".',.-, '--------------\"-\"-'
.......................... ;:s :: -'.::::,,.'.:::::: \" ... . ........ :::7.\".'.-.'.'.'.'.'.'.'.'.'.'.'. 2.32
::::-. ,-.i':-,\". \"t' ..i:i:i:i:ii::!::..--- - .,:..'.:.,--.-:; :.:;-i:i:i:i:i:!:i:-:!:!:!:!:i:i '':: -'-:: - - -' - -:-.----.'\"i:.il ':::\"-.\"'.\"\": \"' '''\ '\ ''* ::':':'::':'\"::: .... :\"'\"'\"\"?',,i ! ;?,',ii?,i!!! 2.5':'\"\"\"'\"\"-\"'- -?-::-:.-: i::i, '\" : ........................ - .......
................. -,, . ,_ ,:::! ....... . ........................................... .............
,., ........ -: -,:,:.::.-.:.:,.-,- ;:,-,.. . ....... , :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: 1.94 220 - x -. ...... ,,, .... , .... ?,.-:,, ,,; .... .......................
:,,-...'.-o-;.:j.;.-ii.:'::,.!½',i'.,.,-,-'.:11;ii:- =============================================================== .73:,'\"'.' ...... ..
:: ,,, .............. ....,....:::\iiiii::::ill .. :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
-\"- ............... ' '' ','\",,:iiiii:::iiiiiiii-. \":::-':\"':':-':-'::::::':::::';::'::::'::'::'::' ':';;:; .........
.:.:.:.:.:. :: :::::::::::::::::::::::::::: . ..: . . :_ _ . 0. :::::::::::::::::::::
0 I 2 3 4 5 6 7 8 9 10
Carbon Aerosol Surface Area
Figure 4. Additional results for midnight at the end of a set of 7-day simulations. During the
seven day simulations the air parcel was kept at 70 rob, 45øN at equinox. The temperature and
amorphous carbon aerosol surface area present were kept constant for each air parcel through
out the 7-day period. The results are plotted as a function of temperature (in Kelvin) and
the amorphous carbon aerosol surface area in m cm -3. Note that each plot has a different
contour interval. The NO/NO, NO/NO and HNO3/NO ratios are dimensionless. The 03
loss time-scale at midnight is in units of days. The additional 03 loss caused by including the
heterogeneous reactions on amorphous carbon aerosol over the 7 day simulation period is shown
as a percentage.
Page 9
LARY ET AL.- CARBON AEROSOLS AND ATMOSPHERIC PHOTOCHEMISTRY 3679
Additional Ozone loss (%)
due to reactions on carbon
0 I 2 3 4 5 6 7 8 9 10
ß :'- :..-.:-- '\":-':.....-'::'::-:::::--i:i: ':! :: i: i: : i i: i: .i i: i:i:i:i: i: i: i:i:i: i:i-:-i:i :: i: :i:i:i: i ........... i:i:::::i::i:. _
ix ..... :':'\"' ' ' ' ' ' \". ' '\"\"'\"'x- ':;-!:':\",\" -
.............. ...:_!, :,, .::-.: ..: _
_ 12.5 -
10 i iiii! .................. := ...... '\"'\" ' ' ' '\"\"'\"\"'\"!-
0 I 2 3 4 5 6 7 8 g 0
Carbon Aerosol Surface Area
4.32 ?:::::::::::::?:?:(::::::
:::::::::::::::::::::::::
3.42 ?:??:::?:?:?:?:?:?::
2.87 \"'\"\":':':\"'\"'::\" ':' \"::\ ------------ i
2.39 ':':\"::':' ' \"
.08 ..................... ?
94 :..
Additional Ozone loss (ppbv)
due to reactions on carbon
0 I 2
25.0 :.:......<
E '
__ :[' \"\"'\"'\" ' '\ \ ....'i
...............
125 I \"':'\" ::\"\ '
100
0 I 2
Carbon Aerosol Surface Area
3 4 5 6 7 8 9 10
I I I I i I I I i.. I ! ....... ! ... ! ..
........ :'\" '½'\"':':\" ; \"' ':-:/'/';i:-i::iiiii:::::i:-i::i!iiiii::i::i::i::i?:::111::11ii?:' '::?:ii: ::i::? : :!i!i ::iii ii::ii?:?:i;i i?:: 231.40 ...........
;:k:'\"\"'½\"::::::::: ....... Zt.,O . . ===================================== ...........
.-.._::..- .... ................... - 11:.!; i:i !:!iii,,i,,i!:,iii::iiiiii.. 5o
......................... :\"' '\": :4;-i 96.50 \"':': '\"':'\"':':\" \" 63.39
................. *\"'\"\"\" \" '\"'''\"''\"':'\"''_'_. o.oo
3 4 5 6 7 8 9 10
Figure 5. The altitude and area dependence of 03 loss by the amorphous carbon aerosol
mechanism. Negative values correspond toan ozone production. (left) Additional 03 loss caused
by including the heterogeneous reactions on amorphous carbon aerosol (in percent) over the 7-day
simulation period. (Right) Additional 03 loss caused by including the heterogeneous reactions
on amorphous carbon aerosol (in ppbv) over the 7-day simulation period.
to ozone loss, whereas in the troposphere the enhanced
levels of NO lead to ozone production.
As there is much more carbon aerosol in the northern
hemisphere than there is in the southern hemisphere,
the heterogeneous reduction of HNO3, NO2, and O3
on amorphous carbon aerosol will give rise to differ-
ent trends in the northern hemisphere and southern
hemisphere. In the troposphere the renoxification that
occurs on carbon aerosols would tend to increase the
ozone concentration. If the carbon aerosols present are
entrained within droplets, then the behavior may be
quite different; this also needs to be examined.
Owing to the shape of .the ozone and NO profiles the
largest additional Oa loss in terms of absolute magni-
tude is largest at higher altitudes. Therefore, if amor-
phous carbon aerosol can be transported from the air-
craft flight corridors up to 2 km, there will be a corre-
sponding effect on the O3 loss rate. Carbon aerosols are
much smaller and lighter than sulphate aerosols, and if,
as suggested by Blake and Karo [1995], most of the soot
is not within sulphate aerosols, there is the possibility
that the carbon aerosol residence time is long enough to
allow them to reach the midstratosphere. This may be,
in part, due to their fractal surface area, which means
that they sediment much slower than a sphere of the
same mass. If this is the case, they may be able to influ-
ence stratospheric chemistry, even up to 30 km. There
may be some indication of this in the comparison of
ATMOS data and simulations presented in Figure 2.
Figure 5 shows that increasing the carbon surface
area from just 0 /m 2 cm -a to 1 /m 2 cm -3 has a
marked effect on stratospheric ozone loss and tropo-
spheric ozone production. Observations show that car-
bon aerosols are definitely present in the midlatitude
lower stratosphere between 12 and 20 km. In relative
terms, it can be seen from Figure 5 that the additional
O3 loss caused by including the heterogeneous reduc-
tion of HNO3 and NO2 on amorphous carbon aerosol is
significant in this region. Solomon et al. [1996] showed
that when a two-dimensional model is constrained with
time-varying aerosol observations the shape of the ob-
served trends in ozone is reproduced, but their magni-
tude is about 50% larger than that which is observed.
The presence of soot in the midlatitude lower strato-
sphere may help to explain part of this discrepancy be-
tween ozone observations and simulations.
Since gas phase HNO3 destruction is so slow, any pro-
cess that is a sink of HNOa is potentially significant.
Midnight
HNOJNO
0 1 2 3 4 5 6 7 8 9 10
250 I
ß ........................................ : :. ': 22.5 .................................. '\"''' \"''\"''' ' ' x ' ::
2o.o ....... E '\"'\"\" -\" ' ' '%' ' '\"' \"'\" '\"\" ' ' ' \"'\ -'\"\"\"''\"\"' -,:.-':
'.-,..-.,'. , :. , ,¾-\"'\"'\"'\"\"'\"\"' '\"\"''\"'\"\"-----------.. - --.,...-.
.,.., :,,:.:.-:,.-.'\"\"\" \"' '\ \"'\" ' ' \":' ' ' - -\".. ß - . ., .... . . ................ . '-% -.::: '
<r: 1.o
...................................... - - ß -__', '
ß o. ,, ......_.., .. .. .........:;......: \"-\"\"'\"'\"'\"\"\"'\"\"'\"\"'\"'\":'i:
10.0 I
0 1 2 3 4 5 6 7 8 9 10
Aerosol Surface Area
15.oo
i:K:!:i:i:i:i:!:!:!:.-':
10.00 ,>..:-\"¾
5.00 ' '
2.00 1.00 0.75 0.50
0.30
Figure 6. The simulated midlatitude HNO3/NO. ra-
tio as a function of altitude and carbon surface area.
Additional Ozone loss (%)
due to reactions on carbon
0 I 2 3 4 5 6 7 8 9 10
ß :'- :..-.:-- '\":-':.....-'::'::-:::::--i:i: ':! :: i: i: : i i: i: .i i: i:i:i:i: i: i: i:i:i: i:i-:-i:i :: i: :i:i:i: i ........... i:i:::::i::i:. _
ix ..... :':'\"' ' ' ' ' ' \". ' '\"\"'\"'x- ':;-!:':\",\" -
.............. ...:_!, :,, .::-.: ..: _
_ 12.5 -
10 i iiii! .................. := ...... '\"'\" ' ' ' '\"\"'\"\"'\"!-
0 I 2 3 4 5 6 7 8 g 0
Carbon Aerosol Surface Area
4.32 ?:::::::::::::?:?:(::::::
:::::::::::::::::::::::::
3.42 ?:??:::?:?:?:?:?:?::
2.87 \"'\"\":':':\"'\"'::\" ':' \"::\ ------------ i
2.39 ':':\"::':' ' \"
.08 ..................... ?
94 :..
Additional Ozone loss (ppbv)
due to reactions on carbon
0 I 2
25.0 :.:......<
E '
__ :[' \"\"'\"'\" ' '\ \ ....'i
...............
125 I \"':'\" ::\"\ '
100
0 I 2
Carbon Aerosol Surface Area
3 4 5 6 7 8 9 10
I I I I i I I I i.. I ! ....... ! ... ! ..
........ :'\" '½'\"':':\" ; \"' ':-:/'/';i:-i::iiiii:::::i:-i::i!iiiii::i::i::i::i?:::111::11ii?:' '::?:ii: ::i::? : :!i!i ::iii ii::ii?:?:i;i i?:: 231.40 ...........
;:k:'\"\"'½\"::::::::: ....... Zt.,O . . ===================================== ...........
.-.._::..- .... ................... - 11:.!; i:i !:!iii,,i,,i!:,iii::iiiiii.. 5o
......................... :\"' '\": :4;-i 96.50 \"':': '\"':'\"':':\" \" 63.39
................. *\"'\"\"\" \" '\"'''\"''\"':'\"''_'_. o.oo
3 4 5 6 7 8 9 10
Figure 5. The altitude and area dependence of 03 loss by the amorphous carbon aerosol
mechanism. Negative values correspond toan ozone production. (left) Additional 03 loss caused
by including the heterogeneous reactions on amorphous carbon aerosol (in percent) over the 7-day
simulation period. (Right) Additional 03 loss caused by including the heterogeneous reactions
on amorphous carbon aerosol (in ppbv) over the 7-day simulation period.
to ozone loss, whereas in the troposphere the enhanced
levels of NO lead to ozone production.
As there is much more carbon aerosol in the northern
hemisphere than there is in the southern hemisphere,
the heterogeneous reduction of HNO3, NO2, and O3
on amorphous carbon aerosol will give rise to differ-
ent trends in the northern hemisphere and southern
hemisphere. In the troposphere the renoxification that
occurs on carbon aerosols would tend to increase the
ozone concentration. If the carbon aerosols present are
entrained within droplets, then the behavior may be
quite different; this also needs to be examined.
Owing to the shape of .the ozone and NO profiles the
largest additional Oa loss in terms of absolute magni-
tude is largest at higher altitudes. Therefore, if amor-
phous carbon aerosol can be transported from the air-
craft flight corridors up to 2 km, there will be a corre-
sponding effect on the O3 loss rate. Carbon aerosols are
much smaller and lighter than sulphate aerosols, and if,
as suggested by Blake and Karo [1995], most of the soot
is not within sulphate aerosols, there is the possibility
that the carbon aerosol residence time is long enough to
allow them to reach the midstratosphere. This may be,
in part, due to their fractal surface area, which means
that they sediment much slower than a sphere of the
same mass. If this is the case, they may be able to influ-
ence stratospheric chemistry, even up to 30 km. There
may be some indication of this in the comparison of
ATMOS data and simulations presented in Figure 2.
Figure 5 shows that increasing the carbon surface
area from just 0 /m 2 cm -a to 1 /m 2 cm -3 has a
marked effect on stratospheric ozone loss and tropo-
spheric ozone production. Observations show that car-
bon aerosols are definitely present in the midlatitude
lower stratosphere between 12 and 20 km. In relative
terms, it can be seen from Figure 5 that the additional
O3 loss caused by including the heterogeneous reduc-
tion of HNO3 and NO2 on amorphous carbon aerosol is
significant in this region. Solomon et al. [1996] showed
that when a two-dimensional model is constrained with
time-varying aerosol observations the shape of the ob-
served trends in ozone is reproduced, but their magni-
tude is about 50% larger than that which is observed.
The presence of soot in the midlatitude lower strato-
sphere may help to explain part of this discrepancy be-
tween ozone observations and simulations.
Since gas phase HNO3 destruction is so slow, any pro-
cess that is a sink of HNOa is potentially significant.
Midnight
HNOJNO
0 1 2 3 4 5 6 7 8 9 10
250 I
ß ........................................ : :. ': 22.5 .................................. '\"''' \"''\"''' ' ' x ' ::
2o.o ....... E '\"'\"\" -\" ' ' '%' ' '\"' \"'\" '\"\" ' ' ' \"'\ -'\"\"\"''\"\"' -,:.-':
'.-,..-.,'. , :. , ,¾-\"'\"'\"'\"\"'\"\"' '\"\"''\"'\"\"-----------.. - --.,...-.
.,.., :,,:.:.-:,.-.'\"\"\" \"' '\ \"'\" ' ' \":' ' ' - -\".. ß - . ., .... . . ................ . '-% -.::: '
<r: 1.o
...................................... - - ß -__', '
ß o. ,, ......_.., .. .. .........:;......: \"-\"\"'\"'\"'\"\"\"'\"\"'\"\"'\"'\":'i:
10.0 I
0 1 2 3 4 5 6 7 8 9 10
Aerosol Surface Area
15.oo
i:K:!:i:i:i:i:!:!:!:.-':
10.00 ,>..:-\"¾
5.00 ' '
2.00 1.00 0.75 0.50
0.30
Figure 6. The simulated midlatitude HNO3/NO. ra-
tio as a function of altitude and carbon surface area.
Page 10
3680 LARY ET AL.' CARBON AEROSOLS AND ATMOSPHERIC PHOTOCHEMISTRY
Additional Ozone loss (%)
due to reactions on carbon
0 I 2 3 4 5 6 7 8 9 10 0 I 2 3 4
I , I ..... ! . !. .... ! J .. ,a:!. :.>::.:.:., .... I , ...! ....... , I ...... ... ::...:. :: ... I .. I 13 I::!i!ii?:::i;iiiii?: I .................... :. 12.8
........................... .... ........................... 12.4
............. '\"'\"\"\"'\"\"'\"\"'' : ''.'-:::&:?a:
, 11.a-: ............. :: : ,..:: o : : :...: : :,. ,.: .... , . ............. . : ::.:.:...::., .... . ........... , ii;:..i::?:ii?:i::',-a.-', :- :ji ! :..::... ..-:.: !, : '-,,'
'0 i!i::i::i!ii ........... '\"\"' '\" -''': ':'%:'\"'i :::! ..................... ''::':':':':'': .......... ::: 1.$ iiii:ii!i!i- iii: '0 11
. :.:.:.:.:.:.::::..: . . ... -. ........,.....:._...::.>:::.'..,..:...,..>.. . :,_:.:__ .._.::.:.:.:._:.............:.- :<..::<.- : : :.: : :.:-:-- .-.- : :.:.:.:.:.:.:.:-:.:-:-:.:.:.:.:
0 I 2 3 4 5 6 7 8 9 10 0
Carbon Aerosol Surface Area
Additional Ozone loss (ppbv)
due to reactions on carbon
5 6 7 8 9 10
i{ -.,.\": ......... '-' i!!ii!iii!i!!!i!!! ......... :::::::::::::::::::::::::::::::::::::::::
\":.¾::,..::i?:!::::!i::::::!:.i::ii: \"-':<'-'-----' -. .. ....'..., .'......- .:.::. . ::: : :: ::::::::
ß '-. .... :::::::::::::::::::::::::
' -. \"k ii::i::iii::i::iii:::, ::: ::::: ::::::::::::::::::::::::::::::::::::::::: $4.$ '\"'\"'\"' '::-:'\"' . i
' ' .:::::::::::.' ,o \":-..:..:.':.'.::.:-? :: : :::::::::::::::::::
......... ::::: ........................ : :r < :.:_, ............................... ß ',t
1õ.0 \"-'-:'-':- ß - ..' .-'.
2 3 4 5 6 7 8 9 10
Carbon Aerosol Surface Area
Figure 7. The seasonal dependence of 03 loss by the amorphous carbon aerosol mechanism.
(Left) Additional 03 loss caused by including the heterogeneous reduction of NO2 on amorphous
carbon aerosol (in percent) over a 7-day simulation. (Right) Additional 03 loss caused by in-
cluding the heterogeneous reduction of NO2 on amorphous carbon aerosol (in ppbv) over a 7-day
simulation.
Figure 6 shows that increasing the carbon surface area
from just 0 to 1/m cm -3 reduces the HNO3/NOw ra-
tio by a factor of about 8. Chatfield [1995] states that
the average free tropospheric HNO3/NOw ratio is be-
tween 1 and 9. As can be seen from Figure 6, this
is entirely consistent with these simulations. It is also
clear that increasing the carbon surface area will sub-
stantially increase NO and the oxidizing capacity of
the troposphere (Figure 5).
Seasonal Dependence
To investigate the seasonal dependence of the mech-
anism, the third set of sensitivity experiments allowed
the time of year to vary between the summer solstice
and the winter solstice. This corresponds to a day
length of between 9.5 and 13 hours for an air parcel
at 45øN in the lower stratosphere. Figure 7 shows that
for relatively high carbon surface areas the additional
03 loss caused by including the heterogeneous reduc-
tion of NO2on amorphous carbon aerosol increases by
moving from the summer solstice to the winter solstice,
whereas at lower carbon surface areas there is little vari-
ation with day length. So the relative importance of the
mechanism tends to increase with the length of the night
for high carbon aerosol oadings. At higher latitudes the
mechanism may lead to less ozone loss at some times,
as there will be more NO2 present to deactivate reac-
tive chlorine, this will, in turn, lead to higher C1ONO2 concentrations.
Summary
If HNO3 and NO2 are heterogeneously reduced on
atmospheric amorphous carbon aerosols produced by,
for example, the combustion of fuel from commercial
air traffic, then a significant renoxification mechanism
exists. This mechanism leads to ozone loss in the strato-
sphere and ozone production in the troposphere. The
stratospheric ozone loss mechanism is almost indepen-
dent of temperature and does not require the presence
of sunlight. The mechanism can operate at all latitudes
where amorphous carbon aerosols are present. The rel-
ative importance of the mechanism increases slightly
with nightlength. Including the heterogeneous reduc-
tion of HNO and NOa in model simulations predicts
a free tropospheric and stratospheric HNO3[NOx ratio
that is in good agreement with observations.
Further laboratory studies are urgently required to
precisely quantify the rate of reduction and investigate
other possible heterogeneous reactions on atmospheric
amorphous carbon aerosols. For example, chlorine and
bromine species such as HOC1 and HOBr may also be
reduced on carbon aerosols. Further field measurements
are required to precisely quantify the amount of amor-
phous carbon aerosols present in the atmosphere. An
assessment of the impact of carbon entrained within
water or sulphuric acid droplets is also required.
Acknowledgments. David Lary is a Royal Society Uni-
versity Research Fellow and wishes to thank the Royal So-
ciety for its support wishes. He also thanks J.A. Pyle for
his support and Robert MacKenzie, and Dudley Shallcross
for very useful conversations. The Centre for Atmospheric
Science is a joint initiative of the Department of Chemistry
and the Department of Apphed Mathematics and Theoret-
ical Physics. This work forms part of the NERC UK Uni-
versities Global Atmospheric Modelling Programme.
References
Baumgardner, D., J. E. Dye, B. Gandrud, K. Barr, K. Kelly,
and K. R. Chan. Refractive, indexes of aerosols in the
Additional Ozone loss (%)
due to reactions on carbon
0 I 2 3 4 5 6 7 8 9 10 0 I 2 3 4
I , I ..... ! . !. .... ! J .. ,a:!. :.>::.:.:., .... I , ...! ....... , I ...... ... ::...:. :: ... I .. I 13 I::!i!ii?:::i;iiiii?: I .................... :. 12.8
........................... .... ........................... 12.4
............. '\"'\"\"\"'\"\"'\"\"'' : ''.'-:::&:?a:
, 11.a-: ............. :: : ,..:: o : : :...: : :,. ,.: .... , . ............. . : ::.:.:...::., .... . ........... , ii;:..i::?:ii?:i::',-a.-', :- :ji ! :..::... ..-:.: !, : '-,,'
'0 i!i::i::i!ii ........... '\"\"' '\" -''': ':'%:'\"'i :::! ..................... ''::':':':':'': .......... ::: 1.$ iiii:ii!i!i- iii: '0 11
. :.:.:.:.:.:.::::..: . . ... -. ........,.....:._...::.>:::.'..,..:...,..>.. . :,_:.:__ .._.::.:.:.:._:.............:.- :<..::<.- : : :.: : :.:-:-- .-.- : :.:.:.:.:.:.:.:-:.:-:-:.:.:.:.:
0 I 2 3 4 5 6 7 8 9 10 0
Carbon Aerosol Surface Area
Additional Ozone loss (ppbv)
due to reactions on carbon
5 6 7 8 9 10
i{ -.,.\": ......... '-' i!!ii!iii!i!!!i!!! ......... :::::::::::::::::::::::::::::::::::::::::
\":.¾::,..::i?:!::::!i::::::!:.i::ii: \"-':<'-'-----' -. .. ....'..., .'......- .:.::. . ::: : :: ::::::::
ß '-. .... :::::::::::::::::::::::::
' -. \"k ii::i::iii::i::iii:::, ::: ::::: ::::::::::::::::::::::::::::::::::::::::: $4.$ '\"'\"'\"' '::-:'\"' . i
' ' .:::::::::::.' ,o \":-..:..:.':.'.::.:-? :: : :::::::::::::::::::
......... ::::: ........................ : :r < :.:_, ............................... ß ',t
1õ.0 \"-'-:'-':- ß - ..' .-'.
2 3 4 5 6 7 8 9 10
Carbon Aerosol Surface Area
Figure 7. The seasonal dependence of 03 loss by the amorphous carbon aerosol mechanism.
(Left) Additional 03 loss caused by including the heterogeneous reduction of NO2 on amorphous
carbon aerosol (in percent) over a 7-day simulation. (Right) Additional 03 loss caused by in-
cluding the heterogeneous reduction of NO2 on amorphous carbon aerosol (in ppbv) over a 7-day
simulation.
Figure 6 shows that increasing the carbon surface area
from just 0 to 1/m cm -3 reduces the HNO3/NOw ra-
tio by a factor of about 8. Chatfield [1995] states that
the average free tropospheric HNO3/NOw ratio is be-
tween 1 and 9. As can be seen from Figure 6, this
is entirely consistent with these simulations. It is also
clear that increasing the carbon surface area will sub-
stantially increase NO and the oxidizing capacity of
the troposphere (Figure 5).
Seasonal Dependence
To investigate the seasonal dependence of the mech-
anism, the third set of sensitivity experiments allowed
the time of year to vary between the summer solstice
and the winter solstice. This corresponds to a day
length of between 9.5 and 13 hours for an air parcel
at 45øN in the lower stratosphere. Figure 7 shows that
for relatively high carbon surface areas the additional
03 loss caused by including the heterogeneous reduc-
tion of NO2on amorphous carbon aerosol increases by
moving from the summer solstice to the winter solstice,
whereas at lower carbon surface areas there is little vari-
ation with day length. So the relative importance of the
mechanism tends to increase with the length of the night
for high carbon aerosol oadings. At higher latitudes the
mechanism may lead to less ozone loss at some times,
as there will be more NO2 present to deactivate reac-
tive chlorine, this will, in turn, lead to higher C1ONO2 concentrations.
Summary
If HNO3 and NO2 are heterogeneously reduced on
atmospheric amorphous carbon aerosols produced by,
for example, the combustion of fuel from commercial
air traffic, then a significant renoxification mechanism
exists. This mechanism leads to ozone loss in the strato-
sphere and ozone production in the troposphere. The
stratospheric ozone loss mechanism is almost indepen-
dent of temperature and does not require the presence
of sunlight. The mechanism can operate at all latitudes
where amorphous carbon aerosols are present. The rel-
ative importance of the mechanism increases slightly
with nightlength. Including the heterogeneous reduc-
tion of HNO and NOa in model simulations predicts
a free tropospheric and stratospheric HNO3[NOx ratio
that is in good agreement with observations.
Further laboratory studies are urgently required to
precisely quantify the rate of reduction and investigate
other possible heterogeneous reactions on atmospheric
amorphous carbon aerosols. For example, chlorine and
bromine species such as HOC1 and HOBr may also be
reduced on carbon aerosols. Further field measurements
are required to precisely quantify the amount of amor-
phous carbon aerosols present in the atmosphere. An
assessment of the impact of carbon entrained within
water or sulphuric acid droplets is also required.
Acknowledgments. David Lary is a Royal Society Uni-
versity Research Fellow and wishes to thank the Royal So-
ciety for its support wishes. He also thanks J.A. Pyle for
his support and Robert MacKenzie, and Dudley Shallcross
for very useful conversations. The Centre for Atmospheric
Science is a joint initiative of the Department of Chemistry
and the Department of Apphed Mathematics and Theoret-
ical Physics. This work forms part of the NERC UK Uni-
versities Global Atmospheric Modelling Programme.
References
Baumgardner, D., J. E. Dye, B. Gandrud, K. Barr, K. Kelly,
and K. R. Chan. Refractive, indexes of aerosols in the
Page 11
LARY ET AL.: CARBON AEROSOLS AND ATMOSPHERIC PHOTOCHEMISTRY 3681
upper troposphere and lower stratosphere, Geophys. Res.
Left., 23 (7), 749-752, 1996.
Barrie, L. A., et al., The influence of mid-latitudinal pol-
lution sources on haze in the Canadian Arctic, A trnos.
Environ., 15, 1407-1419, 1981.
Berry, M. V., Falling fractal flakes, Physica D, 38(1-3), 29-
31. 1989.
Blake, D. F., and K. Kato, Latitudinal distribution of black
carbon soot in the upper troposphere and lower strato-
sphere, J. Geophys. Res., 100 (D4), 7195-7202, 1995.
Cess, R. D., Arctic aerosols- model estimates of interactive
influences upon the surface atmosphere clear-sky radia-
tion budget, Atmos. Environ., 17, 2555-2564, 1983.
Chatfield, R. B., Anomalous HNOs/NOx ratio of remote
tropospheric air- Conversion of I-INOs to formic-acid and
NOx, Geophys. Res. Left., 21 (24), 2705-2708, 1995.
Chipperfield, M.P., M. L. Santee, L. Froidevaux, G. L. Man-
ney, W. G. Read, J. W. Waters, A. E. Roche, and J. M.
Russell, Analysis of UARS data in the southern polar vor-
tex in september 1992 using a chemical-transport model,
J. Geophys. Res., 101(D13), 8861-18881, 1996.
Colbeck, I., and S. Nyeki, Optical and dynamical investiga-
tions of fractal clusters, Sci. Prog. Oxford, 76, 149-166,
1992.
Considine, D. B., A. R. Douglass, and R. S. Stolarski, Het-
erogeneous conversion of N205 to HNOs on background
stratospheric aerosols - comparisons of model results with
data, Geophys. Res. Lett., 19 (4), 397-400, 1992.
DeMore, W. B., et al., Chemical kinetics and photochemical
data for use in stratospheric modeling, Evaluation Num-
ber 10, Jet Propul. Lab., Pasedena, Calif., Publication
94-26, 1994.
Fendel, W., D. Matter, H. Burtscher, and A. Schmidtott,
Interaction between carbon or iron aerosol-particles and
ozone, Atrnos. Environ., 29, 967-973, 1995.
Fendel, W., A. S. Ott, J. Aerosol Sci., 2, S317-S318, 1993.
Fisher, M., and D. J. Lary, Lagrangian four dimensional
variational data assimilation of chemical species, Q. J. R.
Meteorol. Soc., 121(527) Part A, 1681-1704, 1995.
Heintzenberg, J., Size-segregated measurements of partic-
ulate elemental carbon and aerosol light-absorption at
remote Arctic locations, Atmos. Environ., 16(10), 2461-
2469, 1982.
Hansen, A.D. A.,and H. Rosen, Vertical distributions of
particulate carbon, sulfur, and bromine in the arctic haze
and comparison with ground-level measurements at Bar-
row, Alaska, Geophys. Res. Left., 11(5), 381-384, 1984.
Hermann, O., et al., Correlative balloon measurements of
the vertical distribution of N20, NO, NO2, NO, HNOs,
N205, C1ONO2 and total reactive NOv inside the polar
vortex during SESAME, Proceedings of the Third Euro-
pean Symposium on Stratospheric Ozone, Schliersee, Ger-
many, September 18-22, 1995, in press 1996.
K/rcher, B., T. Peter, U.M. Biermann, and U. Schumann,
The initial composition of jet condensation trails, J. At-
rnos. Sci., in press, 1996.
Lary, D. J., Gas phase atmospheric bromine photochemistry,
J. Geophys. Res., 101(D1), 1505-1516, 1996.
Lary, D. J., M.P. Chipperfield, and R. Toumi, The potential
impact of the reaction OH+C10-+HCl+O2 on polar ozone
photochemistry, J. Atrnos. Chern., 21(1), 61-79, 1995.
Lary, D. J., M.P. Chipperfield, R. Toumi, and T. M. Lenton,
Atmospheric heterogeneous bromine chemistry, J. Geo-
phys. Res., 101(D1), 1489-1504, 1996.
Logan, J. A., Trends in the vertical distribution of ozone: An
analysis of ozonesonde data, J. Geophys. Res., 99(D12),
22553-25585, 1994.
Manney, G.L., L. Froidevaux, J. W. Waters, M. L. Santee,
W. G. Reed, D. A. Flower, R. F. Jarnot, and R. W. Zurek.
Arctic ozone depletion observed by U ARS MLS during the
1991/92 winter, Geophys. Res. Left., 23(1), 85-88, 1996.
McElroy, M. B., R. J. Salawitch and K. Minschwaner, The
changing stratosphere, Planet. Space Sci., J0(2-3), 373-
401, 1992.
Newchurch, M. J., et al., Stratospheric NO and NO2 abun-
dances from ATMOS solar-occultation measurements,
Geophys. Res. Left., 23(17), 2373-2376, 1996.
Porch, W. M., and M. C. MacCracken, Parametric study of
the effects of arctic soot on solar-radiation, Atmos. Envi-
ron., 16, 1365-1371, 1982.
Pusechel, R. F., D. F. Blake, K. G. Snetsinger, A.D. A.
Hansen, S. Verma, and K. Kato, Black carbon (soot)
aerosol in the lower stratosphere and upper troposphere,
Geophys. Res. Left., 19(16), 1659-1662, 1992.
Rahn, K. A., and R. McCaffrey, On the origin of the winter
arctic aerosol, Ann. N.Y. Acad. Sci., 338, 486-503, 1980.
Rogaski, C.A., D.M. Golden, and L.R. Williams, The het-
erogeneous reaction of HNOs on model soot compounds,
Abstr. Pap. Am. Chem. Soc., 211(1), 141-ANYL, 1996.
Rosen, H, and A.D. A. Hansen, Role of combustion-
generated carbon particles in the absorption of solar-
radiation in the Arctic haze, Geophys. Res. Left., (5),
461-464, 1984.
Rosen, H., T. Novakov, and B. A. Bodhaine, Soot in the
Arctic, Atmos. Environ., 15, 1371-1374, 1981.
Rosen, H., and T. Novakov, Combustion-generated carbon
particles in the Arctic atmosphere, Nature, 306 (5945),
768-770, 1983.
Schumann, U., Impact of emissions from aircraft and space-
craft upon the atmosphere - An introduction, Paper pre-
sented at International Scientific Colloquium, Cologne,
Germany, April 18-20, 1994.
Shaw, G. E., and K. Stamnes, Arctic haze: Perturbation of
the polar radiation budget, Ann. N.Y. Acad. Sci., 338,
533-539, 1980.
Smith, D.M., W.F. Welch, J.A. Jassim, A.R. Chughtai,
and D.H. Stedman, Soot-ozone reaction kinetics - Spec-
troscopic and gravimetric studies, Appl. Spectros., ,/2(8),
1473-1482, 1988.
Solomon, S., R. W. Portmann, R. R. Garcia, L. W. Thoma-
son, L. R. Poole, and M.P. McCormick, The role of
aerosol variations in anthropogenic ozone depletion at
northern mid-latitudes, J. Geophys. Res., 101(D3), 6713-
6727, 1996.
Stephens, S., M.J. Rossi, and D.M. Golden, The heteroge-
neous reaction of ozone on carbonaceous surfaces, Int. J.
Chem. Kinetics, 18(10), 1133-1149, 1986.
Stonehouse, B., Arctic Air Pollution- Studies in Polar Re-
search, Cambridge Univ. Press, 1986.
Tabor, K., L. Gutzwiller, and M. J. Rossi, The heteroge-
neous interaction of NO2 with amorphous-carbon, Geo-
phys. Res. Left., 20(14), 1431-1434, 1993.
Tabor, K., L. Gutzwiller, and M. J. Rossi, The heteroge-
neous interaction of NO2 with amorphous-carbon at am-
bient temperature, J. Phys. Chem., 98(24), 6172-6186,
1994.
Thlibi, J., and J. C. Petit, A study of the NOv/Soot inter-
action in the temperature range 303-1223 K, Paper pre-
sented at International Scientific Colloquium, Cologne,
Germany, April 18-20, 1994.
Toumi, R. S. Bekki and R. Cox, A model study of ATMOS
observations and the heterogeneous loss of N20 by the
sulfate aerosol ayer, J. Atmos. Uhern., 16(2), 135-144,
1993.
World Meteorological Organisation, Scientific assessment of
stratospheric ozone: 1991, Rep. 25, WMO Global Ozone
Res. and Monit. Proj., Geneva, 1992.
World Meteorological Organisation, Scientific assessment of
upper troposphere and lower stratosphere, Geophys. Res.
Left., 23 (7), 749-752, 1996.
Barrie, L. A., et al., The influence of mid-latitudinal pol-
lution sources on haze in the Canadian Arctic, A trnos.
Environ., 15, 1407-1419, 1981.
Berry, M. V., Falling fractal flakes, Physica D, 38(1-3), 29-
31. 1989.
Blake, D. F., and K. Kato, Latitudinal distribution of black
carbon soot in the upper troposphere and lower strato-
sphere, J. Geophys. Res., 100 (D4), 7195-7202, 1995.
Cess, R. D., Arctic aerosols- model estimates of interactive
influences upon the surface atmosphere clear-sky radia-
tion budget, Atmos. Environ., 17, 2555-2564, 1983.
Chatfield, R. B., Anomalous HNOs/NOx ratio of remote
tropospheric air- Conversion of I-INOs to formic-acid and
NOx, Geophys. Res. Left., 21 (24), 2705-2708, 1995.
Chipperfield, M.P., M. L. Santee, L. Froidevaux, G. L. Man-
ney, W. G. Read, J. W. Waters, A. E. Roche, and J. M.
Russell, Analysis of UARS data in the southern polar vor-
tex in september 1992 using a chemical-transport model,
J. Geophys. Res., 101(D13), 8861-18881, 1996.
Colbeck, I., and S. Nyeki, Optical and dynamical investiga-
tions of fractal clusters, Sci. Prog. Oxford, 76, 149-166,
1992.
Considine, D. B., A. R. Douglass, and R. S. Stolarski, Het-
erogeneous conversion of N205 to HNOs on background
stratospheric aerosols - comparisons of model results with
data, Geophys. Res. Lett., 19 (4), 397-400, 1992.
DeMore, W. B., et al., Chemical kinetics and photochemical
data for use in stratospheric modeling, Evaluation Num-
ber 10, Jet Propul. Lab., Pasedena, Calif., Publication
94-26, 1994.
Fendel, W., D. Matter, H. Burtscher, and A. Schmidtott,
Interaction between carbon or iron aerosol-particles and
ozone, Atrnos. Environ., 29, 967-973, 1995.
Fendel, W., A. S. Ott, J. Aerosol Sci., 2, S317-S318, 1993.
Fisher, M., and D. J. Lary, Lagrangian four dimensional
variational data assimilation of chemical species, Q. J. R.
Meteorol. Soc., 121(527) Part A, 1681-1704, 1995.
Heintzenberg, J., Size-segregated measurements of partic-
ulate elemental carbon and aerosol light-absorption at
remote Arctic locations, Atmos. Environ., 16(10), 2461-
2469, 1982.
Hansen, A.D. A.,and H. Rosen, Vertical distributions of
particulate carbon, sulfur, and bromine in the arctic haze
and comparison with ground-level measurements at Bar-
row, Alaska, Geophys. Res. Left., 11(5), 381-384, 1984.
Hermann, O., et al., Correlative balloon measurements of
the vertical distribution of N20, NO, NO2, NO, HNOs,
N205, C1ONO2 and total reactive NOv inside the polar
vortex during SESAME, Proceedings of the Third Euro-
pean Symposium on Stratospheric Ozone, Schliersee, Ger-
many, September 18-22, 1995, in press 1996.
K/rcher, B., T. Peter, U.M. Biermann, and U. Schumann,
The initial composition of jet condensation trails, J. At-
rnos. Sci., in press, 1996.
Lary, D. J., Gas phase atmospheric bromine photochemistry,
J. Geophys. Res., 101(D1), 1505-1516, 1996.
Lary, D. J., M.P. Chipperfield, and R. Toumi, The potential
impact of the reaction OH+C10-+HCl+O2 on polar ozone
photochemistry, J. Atrnos. Chern., 21(1), 61-79, 1995.
Lary, D. J., M.P. Chipperfield, R. Toumi, and T. M. Lenton,
Atmospheric heterogeneous bromine chemistry, J. Geo-
phys. Res., 101(D1), 1489-1504, 1996.
Logan, J. A., Trends in the vertical distribution of ozone: An
analysis of ozonesonde data, J. Geophys. Res., 99(D12),
22553-25585, 1994.
Manney, G.L., L. Froidevaux, J. W. Waters, M. L. Santee,
W. G. Reed, D. A. Flower, R. F. Jarnot, and R. W. Zurek.
Arctic ozone depletion observed by U ARS MLS during the
1991/92 winter, Geophys. Res. Left., 23(1), 85-88, 1996.
McElroy, M. B., R. J. Salawitch and K. Minschwaner, The
changing stratosphere, Planet. Space Sci., J0(2-3), 373-
401, 1992.
Newchurch, M. J., et al., Stratospheric NO and NO2 abun-
dances from ATMOS solar-occultation measurements,
Geophys. Res. Left., 23(17), 2373-2376, 1996.
Porch, W. M., and M. C. MacCracken, Parametric study of
the effects of arctic soot on solar-radiation, Atmos. Envi-
ron., 16, 1365-1371, 1982.
Pusechel, R. F., D. F. Blake, K. G. Snetsinger, A.D. A.
Hansen, S. Verma, and K. Kato, Black carbon (soot)
aerosol in the lower stratosphere and upper troposphere,
Geophys. Res. Left., 19(16), 1659-1662, 1992.
Rahn, K. A., and R. McCaffrey, On the origin of the winter
arctic aerosol, Ann. N.Y. Acad. Sci., 338, 486-503, 1980.
Rogaski, C.A., D.M. Golden, and L.R. Williams, The het-
erogeneous reaction of HNOs on model soot compounds,
Abstr. Pap. Am. Chem. Soc., 211(1), 141-ANYL, 1996.
Rosen, H, and A.D. A. Hansen, Role of combustion-
generated carbon particles in the absorption of solar-
radiation in the Arctic haze, Geophys. Res. Left., (5),
461-464, 1984.
Rosen, H., T. Novakov, and B. A. Bodhaine, Soot in the
Arctic, Atmos. Environ., 15, 1371-1374, 1981.
Rosen, H., and T. Novakov, Combustion-generated carbon
particles in the Arctic atmosphere, Nature, 306 (5945),
768-770, 1983.
Schumann, U., Impact of emissions from aircraft and space-
craft upon the atmosphere - An introduction, Paper pre-
sented at International Scientific Colloquium, Cologne,
Germany, April 18-20, 1994.
Shaw, G. E., and K. Stamnes, Arctic haze: Perturbation of
the polar radiation budget, Ann. N.Y. Acad. Sci., 338,
533-539, 1980.
Smith, D.M., W.F. Welch, J.A. Jassim, A.R. Chughtai,
and D.H. Stedman, Soot-ozone reaction kinetics - Spec-
troscopic and gravimetric studies, Appl. Spectros., ,/2(8),
1473-1482, 1988.
Solomon, S., R. W. Portmann, R. R. Garcia, L. W. Thoma-
son, L. R. Poole, and M.P. McCormick, The role of
aerosol variations in anthropogenic ozone depletion at
northern mid-latitudes, J. Geophys. Res., 101(D3), 6713-
6727, 1996.
Stephens, S., M.J. Rossi, and D.M. Golden, The heteroge-
neous reaction of ozone on carbonaceous surfaces, Int. J.
Chem. Kinetics, 18(10), 1133-1149, 1986.
Stonehouse, B., Arctic Air Pollution- Studies in Polar Re-
search, Cambridge Univ. Press, 1986.
Tabor, K., L. Gutzwiller, and M. J. Rossi, The heteroge-
neous interaction of NO2 with amorphous-carbon, Geo-
phys. Res. Left., 20(14), 1431-1434, 1993.
Tabor, K., L. Gutzwiller, and M. J. Rossi, The heteroge-
neous interaction of NO2 with amorphous-carbon at am-
bient temperature, J. Phys. Chem., 98(24), 6172-6186,
1994.
Thlibi, J., and J. C. Petit, A study of the NOv/Soot inter-
action in the temperature range 303-1223 K, Paper pre-
sented at International Scientific Colloquium, Cologne,
Germany, April 18-20, 1994.
Toumi, R. S. Bekki and R. Cox, A model study of ATMOS
observations and the heterogeneous loss of N20 by the
sulfate aerosol ayer, J. Atmos. Uhern., 16(2), 135-144,
1993.
World Meteorological Organisation, Scientific assessment of
stratospheric ozone: 1991, Rep. 25, WMO Global Ozone
Res. and Monit. Proj., Geneva, 1992.
World Meteorological Organisation, Scientific assessment of
Page 12
3682 LARY ET AL.: CARBON AEROSOLS AND ATMOSPHERIC PHOTOCHEMISTRY
stratospheric ozone: 1994, Rep. 37, WMO Global Ozone
Res. and Monit. Proj., Geneva, 1994.
D. J. Lary and A.M. Lee, Centre For Atmospheric
Science, Department of Chemistry, Cambridge University,
Lensfield Road, Cambridge, CB2 1EW, England. (e-mail:
david@atm.ch.cam.ac.uk)
M. J. Newchurch, Earth System Science Lab., University
of Alabama in Huntsville, Huntsville, AL 35899, U.S.A.
M. Pirre and J. B. Renard, Laboratoire de Phsyique et
Chimie de l'Environement. CNRS, Orleans, France.
R. Toumi, Department of Physics, Imperial College, Lon-
don, SW7 2BZ, England.
(Received November 22, 1995; revised August 26, 1996;
accepted August 26, 1996.)
stratospheric ozone: 1994, Rep. 37, WMO Global Ozone
Res. and Monit. Proj., Geneva, 1994.
D. J. Lary and A.M. Lee, Centre For Atmospheric
Science, Department of Chemistry, Cambridge University,
Lensfield Road, Cambridge, CB2 1EW, England. (e-mail:
david@atm.ch.cam.ac.uk)
M. J. Newchurch, Earth System Science Lab., University
of Alabama in Huntsville, Huntsville, AL 35899, U.S.A.
M. Pirre and J. B. Renard, Laboratoire de Phsyique et
Chimie de l'Environement. CNRS, Orleans, France.
R. Toumi, Department of Physics, Imperial College, Lon-
don, SW7 2BZ, England.
(Received November 22, 1995; revised August 26, 1996;
accepted August 26, 1996.)
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