New particle formation from the reactions of ozone with indene and styrene

This work reports the experimental study of the ozonolysis of indene in the presence of SO2 and the reaction conditions leading to the formation of secondary aerosols. The reactions have been carried out in a Teflon chamber filled with synthetic air mixtures at atmospheric pressure and room temperature. As in the case of styrene, SO2 plays a key role in the oxidation of the Criegee intermediates and enhances the formation of particulate matter. Thus, for the ozonolysis of indene, nucleation was observed for reacted indene concentrations above (4.5 ± 0.8) × 1011 molecule cm−3 in the absence of SO2 while new particle formation was observed for concentrations one order of magnitude lower, (3 ± 1) × 1010 molecule cm−3, in the presence of SO2. Within the detection limit of the system, SO2 concentrations remained constant during the experiments. The formation of secondary aerosols in the smog chamber was inhibited by H2O and so the potential formation of secondary aerosols under atmospheric conditions depends on the concentration of SO2 and relative humidity. Computational calculations have been performed for the ozonolysis of both indene and styrene in the presence of SO2 and water to identify the reaction channels and species responsible for new particle formation. The release of SO3 and its subsequent conversion into H2SO4 from the reaction of the Criegee intermediate H2COO in the ozonolysis of styrene makes this aromatic have a high potential of aerosol formation in the atmosphere. On the other hand, quantitative conversion of SO2 into SO3 does not occur following the ozonolysis of indene.