7A.1 Implementation of heterogeneous chemistry and effects of dust aerosols on photolysis rates in WRF-Chem

Kumar, Rajesh, M. C. Barth, G. G. Pfister, National Center for Atmospheric Research (NCAR), G. R. Carmichael, University of Iowa, C. Knote, NCAR, M. Naja, N. Ojha, and T. Sarangi, Aryabhatta Research Institute of Observational-Sciences

Dust aerosols can affect tropospheric chemistry by perturbing photolysis rates and by providing large surfaces for heterogeneous chemistry. Many studies have focused on understanding these impacts but such studies are nearly absent over northern India, where dust aerosols contribute significantly to the aerosol loading during the pre-monsoon season. This study analyzes the impact of a typical pre-monsoon season dust storm on the tropospheric composition in northern India by updating the WRF-Chem model to include 12 heterogeneous reactions on dust surfaces and allow for dust particles to affect photolysis rates. Model results suggest that dust aerosols can decrease photolysis rates by 40-50% at the surface in high dust laden regions and decrease concentration of different trace gases such as ozone, NOy and HOx compounds by 20-100%. More detailed discussions about the implementation procedure, the relative humidity dependence of uptake coefficients, and the impacts of radiative effects and heterogeneous processes on tropospheric chemistry will be presented.