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Journal article

Effect of chemical degradation on fluxes of reactive compounds - A study with a stochastic Lagrangian transport model

Rinne J, Markkanen T, Ruuskanen T, Petäjä T, Keronen P, Tang M, Crowley J, Rannik Ü, Vesala T...(+9 more)

Atmospheric Chemistry and Physics, vol. 12, issue 11 (2012) pp. 4843-4854

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Abstract

In the analyses of VOC fluxes measured above plant canopies, one usually
assumes the flux above canopy to equal the exchange at the surface. Thus
one assumes the chemical degradation to be much slower than the
turbulent transport. We used a stochastic Lagrangian transport model in
which the chemical degradation was described as first order decay in
order to study the effect of the chemical degradation on above canopy
fluxes of chemically reactive species. With the model we explored the
sensitivity of the ratio of the above canopy flux to the surface
emission on several parameters such as chemical lifetime of the
compound, friction velocity, stability, and canopy density. Our results
show that friction velocity and chemical lifetime affected the loss
during transport the most. The canopy density had a significant effect
if the chemically reactive compound was emitted from the forest floor.
We used the results of the simulations together with oxidant data
measured during HUMPPA-COPEC-2010 campaign at a Scots pine site to
estimate the effect of the chemistry on fluxes of three typical biogenic
VOCs, isoprene, alpha-pinene, and beta-caryophyllene. Of these, the
chemical degradation had a major effect on the fluxes of the most
reactive species beta-caryophyllene, while the fluxes of alpha-pinene
were affected during nighttime. For these two compounds representing the
mono- and sesquiterpenes groups, the effect of chemical degradation had
also a significant diurnal cycle with the highest chemical loss at
night. The different day and night time loss terms need to be accounted
for, when measured fluxes of reactive compounds are used to reveal
relations between primary emission and environmental parameters.

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