So2 Effect on Secondary Organic Aerosol Formation: Experimental and Modelled Results

Abstract: The effect of SO2 in the photooxidation of a mixture of anthropogenic precursors is studied. For that purpose, five experiments with a mixture of 1,3,5-trimethylbenzene, o-xylene, toluene and octane in the presence of HONO were carried out in the EUPHORE outdoor chamber by adding different initial SO2 concentrations in each experiment. The experimental secondary organic aerosol obtained in the experiments was compared with the aerosol simulated by two air quality models (CMAQ and CHIMERE) under the same initial conditions. A simplified version of the models was designed in order to consider the closed system of the chamber, where only gas phase chemistry and aerosol formation take place. While the experimental results show a clear increase of the aerosol formed in the presence of increasing SO2 concentrations, the models do not consider this enhancement in the simulations. The behaviour of the models points out the need of a way to implement this SO2 effect on anthropogenic secondary organic aerosol.