23. Impact of Aerosol Activation on Modelled Regional Particulate Matter Mass and Size Distribution Due to Cloud Processing

Aerosol activation is a key process in aerosol-AQ cloud interaction. Although it is widely studied within the climate modeling community it has not been attracting significant attention within the air quality modeling community. In this study an off-line, sectional, chemically-speciated regional air quality model, AURAMS, has been used to assess the impact of aerosol activation on the modelled regional particulate matter (PM) mass concentration and size distribution. Asimple activation scheme based on an empirical relationship between cloud droplet number density and aerosol number density is compared to a more physically-based activation scheme. Model simulations were compared to aircraft observations obtained during the 2004 ICARTT field campaign. Modelled aerosol light extinction and column aerosol optical depth (AOD) were computed in three different ways in the current study. Two of them based on Mie calculations and one empirical reconstructed mass extinction method. The magnitude of the modeled AOD varies significantly depending on the approach. The impact of different aerosol activation schemes on the modelled AOD in this case is generally in the range of 20–30 % for the two Mie methods. As the empirical reconstructed mass extinction method is not size dependent, it is less sensitive to aerosol activation.