Synergetic formation of secondary inorganic and organic aerosol: effect of SOsub2/sub and NHsub3/sub on particle formation and growth

摘要

The effects of SOsub2/sub and NHsub3/sub on secondary organic aerosol formation have rarely been investigated together, while the interactive effects between inorganic and organic species under highly complex pollution conditions remain uncertain. Here we studied the effects of SOsub2/sub and NHsub3/sub on secondary aerosol formation in the photooxidation system of toluene∕NOsubix/i/sub in the presence or absence of Alsub2/subOsub3/sub seed aerosols in a 2?msup3/sup smog chamber. The presence of SOsub2/sub increased new particle formation and particle growth significantly, regardless of whether NHsub3/sub was present. Sulfate, organic aerosol, nitrate, and ammonium were all found to increase linearly with increasing SOsub2/sub concentrations. The increases in these four species were more obvious under NHsub3/sub-rich conditions, and the generation of nitrate, ammonium, and organic aerosol increased more significantly than sulfate with respect to SOsub2/sub concentration, while sulfate was the most sensitive species under NHsub3/sub-poor conditions. The synergistic effects between SOsub2/sub and NHsub3/sub in the heterogeneous process contributed greatly to secondary aerosol formation. Specifically, the generation of NHsub4/subNOsub3/sub was found to be highly dependent on the surface area concentration of suspended particles, and increased most significantly with SOsub2/sub concentration among the four species under NHsub3/sub-rich conditions. Meanwhile, the absorbed NHsub3/sub might provide a liquid surface layer for the absorption and subsequent reaction of SOsub2/sub and organic products and, therefore, enhance sulfate and secondary organic aerosol (SOA) formation. This effect mainly occurred in the heterogeneous process and resulted in a significantly higher growth rate of seed aerosols compared to without NHsub3/sub. By applying positive matrix factorisation (PMF) analysis to the AMS data, two factors were identified for the generated SOA. One factor, assigned to less-oxidised organic aerosol and some oligomers, increased with increasing SOsub2/sub under NHsub3/sub-poor conditions, mainly due to the well-known acid catalytic effect of the acid products on SOA formation in the heterogeneous process. The other factor, assigned to the highly oxidised organic component and some nitrogen-containing organics (NOC), increased with SOsub2/sub under a NHsub3/sub-rich environment, with NOC (organonitrates and NOC with reduced N) contributing most of the increase.