Influence of the aerosol solar extinction on photochemistry during the 2010 Russian wildfires episode

Abstract

Abstract. In this work, impact of aerosol solar extinction on the photochemistry over eastern Europe during the 2010 wildfires episode is discussed for the period from 5 to 12 August 2010, which coincides to the peak of fire activity. The methodology is based on an on-line coupling between the chemistry-transport model CHIMERE (extended by an aerosol optical module) and the radiative transfer code TUV. Results of simulations indicate an important influence of the aerosol solar extinction, in terms of intensity and spatial extent, with a reduction of the photolysis rates of NO2 and O3 up to 50% (in diurnal-averaged) along the aerosol plume transport. At a regional scale, these changes in photolysis rates lead to a 3–15% increase in the NO2 daytime concentration and to an ozone reduction near the surface of 1–12%. The ozone reduction is shown to occur over the entire boundary layer, where aerosols are located. Also, comparisons of simulations with air quality measurements over Moscow show that the inclusion of the aerosol feedback tends to slightly improve performance of the model in simulating NO2 and O3 ground concentrations. In term of air quality prediction, the O3 peak reduction when including aerosol feedback results in a non-negligible difference in the predicted exceedance of alert threshold compared to the simulation without aerosol feedback, in coherence with measurements. Finally, the total aerosol mass concentration (PM10) is shown to be decreased by 1–2 %, on average during the studied period, caused by a reduced formation of secondary aerosols such as sulphates and secondary organics (4–10%) when aerosol impact on photolysis rates is included.