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Journal article

Sources of organic carbon in fine particulate matter in northern European urban air

Saarikoski S, Timonen H, Saarnio K, Aurela M, Jarvi L, Keronen P, Kerminen V, Hillamo R ...see all

Atmos. Chem. Physics, vol. 8, issue 20 (2008) pp. 6281-6295

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A major fraction of fine particle matter consists of organic carbon
(OC) but its origin is still inadequately known. In this study the
sources of OC were investigated in the northern European urban environment
in Helsinki, Finland. Measurements were carried out over one year
and they included both filter (PM1) and online methods. From the
filter samples OC, elemental carbon (EC), water-soluble OC (WSOC),
levoglucosan and major ions were analyzed. Filter data together with
the concentrations of inorganic gases were analyzed by Positive matrix
factorization (PMF) in order to find the sources of OC (and WSOC)
on an annual as well as on a seasonal basis. In order to study the
diurnal variation of sources, OC and EC were measured by a semicontinuous
OC/EC analyzer and major ions were determined by a Particle-into-Liquid
Sampler coupled to ion chromatographs. According to PMF, OC concentrations
were impacted by four sources: biomass combustion, traffic, long-range
transport and secondary production. On an annual basis the OC concentration
was dominated by secondary organic aerosol (SOA). Its contribution
to OC was as high as 64% in summer, which besides anthropogenic
sources may also result from the large biogenic volatile organic
carbon (VOC) emissions in the boreal region. In winter biomass combustion
constituted the largest fraction in OC due to domestic wood combustion
for heating purposes. Traffic contributed to OC from 15 to 27%.
Regarding the diurnal variation, the contribution from traffic was
higher from 08:00 to 18:00 on weekdays than on weekends. The contribution
from long-range transport to OC was 24% on average. All four sources
also influenced the WSOC concentrations, however, the contribution
of SOA was significantly larger for WSOC than OC.

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  • S Saarikoski

  • H Timonen

  • K Saarnio

  • M Aurela

  • L Jarvi

  • P Keronen

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