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Abstract:
Chemistry transport models (CTMs) are an indispensable tool for studying
and predicting atmospheric and climate effects associated with
carbonaceous aerosol from open biomass burning (BB); this type of
aerosol is known to contribute significantly to both global radiative
forcing and to episodes of air pollution in regions affected by
wildfires. Improving model performance requires systematic comparison of
simulation results with measurements of BB aerosol and elucidation of
possible reasons for discrepancies between them, which, by default, are
frequently attributed in the literature to uncertainties in emission
data. Based on published laboratory data on the atmospheric evolution of
BB aerosol and using the volatility basis set (VBS) framework for
organic aerosol modeling, we examined the importance of taking
gas-particle partitioning and oxidation of semivolatile organic
compounds (SVOCs) into account in simulations of the mesoscale evolution
of smoke plumes from intense wildfires that occurred in western Russia
in 2010. Biomass burning emissions of primary aerosol components were
constrained with PM10 and CO data from the air pollution monitoring
network in the Moscow region. The results of the simulations performed
with the CHIMERE CTM were evaluated by considering, in particular, the
ratio of smoke-related enhancements in PM10 and CO concentrations (Delta
PM10 and Delta CO) measured in Finland (in the city of Kuopio), nearly
1000 km downstream of the fire emission sources. It is found that while
the simulations based on a "conventional" approach to BB aerosol
modeling (disregarding oxidation of SVOCs and assuming organic aerosol
material to be non-volatile) strongly underestimated values of Delta
PM10/Delta CO observed in Kuopio (by a factor of 2), employing the
"advanced" representation of atmospheric processing of organic aerosol
material resulted in bringing the simulations to a much closer agreement
with the ground measurements. Furthermore, taking gas-particle
partitioning and oxidation of SVOCs into account is found to result in a
major improvement of the agreement of simulations and satellite
measurements of aerosol optical depth, as well as in considerable
changes in predicted aerosol composition and top-down BB aerosol
emission estimates derived from AOD measurements.
