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 SO 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, SO 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) × 10 molecule cm in the absence of SO while new particle formation was observed for concentrations one order of magnitude lower, (3 ± 1) × 10 molecule cm, in the presence of SO. Within the detection limit of the system, SO concentrations remained constant during the experiments. The formation of secondary aerosols in the smog chamber was inhibited by HO and so the potential formation of secondary aerosols under atmospheric conditions depends on the concentration of SO and relative humidity. Computational calculations have been performed for the ozonolysis of both indene and styrene in the presence of SO and water to identify the reaction channels and species responsible for new particle formation. The release of SO and its subsequent conversion into HSO from the reaction of the Criegee intermediate HCOO 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 SO into SO does not occur following the ozonolysis of indene.