Synergistic Effects of SO₂ and NH₃ Coexistence on SOA Formation from Gasoline Evaporative Emissions

Abstract

Vehicular evaporative emissions make an increasing contribution to anthropogenic sources of volatile organic compounds (VOCs), thus contributing to secondary organic aerosol (SOA) formation. However, few studies have been conducted on SOA formation from vehicle evaporative VOCs under complex pollution conditions with the coexistence of NO x , SO 2 , and NH 3 . In this study, the synergistic effects of SO 2 and NH 3 on SOA formation from gasoline evaporative VOCs with NO x were examined using a 30 m 3 smog chamber with the aid of a series of mass spectrometers. Compared with the systems involving SO 2 or NH 3 alone, SO 2 and NH 3 coexistence had a greater promotion effect on SOA formation, which was larger than the cumulative effect of the two promotions alone. Meanwhile, contrasting effects of SO 2 on the oxidation state (OSc) of SOA in the presence or absence of NH 3 were observed, and SO 2 could further increase the OSc with the coexistence of NH 3 . The latter was attributed to the synergistic effects of SO 2 and NH 3 coexistence on SOA formation, wherein N−S−O adducts can be formed from the reaction of SO 2 with N-heterocycles generated in the presence of NH 3 . Our study contributes to the understanding of SOA formation from vehicle evaporative VOCs under highly complex pollution conditions and its atmospheric implications.

Combined Smog Chamber/Oxidation Flow Reactor Study on Aging of Secondary Organic Aerosol from Photooxidation of Aromatic Hydrocarbons

“…However, each technique also has its own disadvantages. Traditional SC experiments often fail to achieve the degree of oxidation observed in the atmosphere due to their inadequate oxidant exposure (oxidant concentration × time, molecules cm –3 s) compared to that in the ambient air. , Additionally, the capacity of SC to study reactions lasting several days or weeks is impeded by the loss of particles and organic vapors to the chamber wall. , Due to the limitations of simulated reaction time (several hours), SC experiments are not conducive to understanding the subsequent reactions of the gas-phase organic intermediates formed from the photooxidation of VOCs. In contrast, high OH concentrations (up to 10 9 –10 10 molecules cm –3 ) can be generated in OFR experiments, which can simulate the aging process of VOCs at longer timescales (equivalent to a few days to weeks). , However, the extremely high OH concentrations in OFR experiments may lead to large differences in the reaction pathway and product distribution of VOC photooxidation from those in the ambient air .…”