Modeling the Effects of Heterogeneous Chemistry on Aerosol Optical Properties and Atmospheric Chemistry

Heterogeneous reactions on aerosols are important for atmospheric chemistry models. But most models only consider that heterogeneous reactions remove gas phase species through adsorption and uptake and/or through reaction thereby converting one gas phase species into another. The changes of concentrations of gases and particles after heterogeneous chemistry affect atmospheric chemistry directly and indirectly. Laboratory studies have already shown that heterogeneous reactions can change the optical properties of aerosols. In order to fully understand and assess the importance of these results on photochemical processes and tropospheric chemistry, it is essential to use the data in atmospheric chemistry models. A box model is developed to study the effects of the heterogeneous uptakes of gases on aerosol optical properties and the photochemical oxidant cycle. This box model includes gas chemistry, atmospheric radiation, and an aerosol module to deal with the chemical interactions between gases and particles. Heterogeneous chemistry is included and the complex of aerosol surface is considered with it. The aerosol module also calculates the optical properties of particles. The radiative fluxes and photolysis rates are calculated using the NCAR Tropospheric Ultraviolet-Visible (TUV) radiation model, which is a one-dimensional solver for actinic flux and photolysis frequencies. It can consider the influence of aerosols and clouds on gas-phase photolysis rates and UV fluxes. The importance of heterogeneous chemistry on the photochemical oxidant cycle is shown in the box model studies. The model will also be used to explore the data from the INTEX-B field experiment.