Effects of two transition metal sulfate salts on secondary organic aerosol formation in toluene/NOx photooxidation
摘要
Aerosol phase reactions play a very important role on secondary organic aerosol （SOA） formation, and metal-containing aerosols are important components in the atmosphere. In this study, we tested the effects of two transition metal sulfate salts, manganese sulfate （MnSO4） and zinc sulfate （ZnSO4）, on the photochemical reactions of a toluene/NOx photooxidation system in a 2 m3 smog chamber. By comparing photochemical reaction products of experiments with and without transition metal sulfate seed aerosols, we evaluated the effects of transition metal sulfate seed aerosols on toluene consumption, NOx conversion and the formation of ozone and SOA. MnSO4 and ZnSO4 seed aerosols were found to have similar effects on photochemical reactions, both enhance the SOA production, while showing negligible effects on the gas phase compounds. These observations are consistent when varying metal sulfate aerosol concentrations. This is attributed to the catalytic effects of MnSO4 and ZnSO4 seed aerosols which may enhance the formation of condensable semivolatile compounds. Their subsequent partitioning into the aerosol phase leads to the observed SOA formation enhancement.