Study of the aerosol formation from the mixture of isoprene and dimethyl sulfide in the presence of nitrogen oxide.

摘要

Past and current research findings suggest that the acid catalyzed heterogeneous reaction theory narrows the gap between the ambient secondary organic aerosol (SOA) data and the predicted SOA data using the precursor flux multiplied by the SOA yield determined from chamber experiments. In this study, a reduced sulfur compound that is predominantly from oceanic sources, dimethyl sulfide (DMS), was proposed to be an additional source of aerosol acidity. SOA created from the photooxidation of a mixture of isoprene and DMS was studied using a Teflon film indoor chamber and for different NO x concentrations (40 to 220 ppb) and relative humidity values of 12%, 42% and 80%. Results obtained from chamber experiments showed that the isoprene SOA yield is increased by 30% to 150% in the presence of DMS. The impact of MSA on the SOA formation produced from photooxidation of isoprene in the presence of NOx was investigated in a 2 m³ Teflon film indoor chamber. Our study showed that MSA aerosol can significantly increase the isoprene SOA. In order to model the SOA formation in the presence of MSA and H 2SO4, a prediction model of DMS photooxidation was developed. The most recently reported reactions with their rate constants have been included. The model included in this study predicted that concentrations of both MSA and H2SO4 would significantly increase due to heterogeneous chemistry, and this was well substantiated with experimental data. To confirm the DMS effect on SOA formation in the ambient air, the effect of MSA on increasing the SOA mass and the relative contribution of SO2 and DMS to sulfate were evaluated through ambient aerosol samples. Our results suggest that DMS is a significant source of acidic aerosol (H2SO4 and MSA) in the coastal area and in the land surrounded by fresh water wetland or salt marsh.