Abstract
Peroxy acetyl nitrate (PAN) is a key component of photochemical smog and plays an important role in atmospheric chemistry. Though it has been known that PAN is produced via reactions of nitrogen oxides (NOx) with some volatile organic compounds (VOCs), it is difficult to quantify the contributions of individual precursor species. Here we use an explicit photochemical model – Master Chemical Mechanism (MCM) model – to dissect PAN formation and identify principal precursors, by analyzing measurements made in Beijing in summer 2008. PAN production was sensitive to both NOx and VOCs. Isoprene was the predominant VOC precursor at suburb with biogenic impact, whilst anthropogenic hydrocarbons dominated at downtown. PAN production was attributable to a relatively small class of compounds including NOx, xylenes, trimethylbenzenes, trans/cis-2-butenes, toluene, and propene. MCM can advance understanding of PAN photochemistry to a species level, and provide more relevant recommendations for mitigating photochemical pollution in large cities.
Highlights
Peroxy acetyl nitrate (PAN, CH3C(O)O2NO2) is a key pollutant in photochemical smog
We analyzed measurements of PAN and PAN precursors made at a suburban site as well as hydrocarbon data collected at downtown Beijing
In-situ photochemical production and transport of urban plumes were the processes contributing to PAN pollution at the study site
Summary
Peroxy acetyl nitrate (PAN, CH3C(O)O2NO2) is a key pollutant in photochemical smog It is a cause of eye irritation and negatively affects vegetation, and is a potential mutagen for skin cancer (Stephens, 1969). It is an important player in atmospheric chemistry by acting as a reservoir of nitrogen oxides (NOx). It is primarily formed in the industrialized/urbanized regions with abundant NOx, and can be transported over long distances at low temperatures to remote regions and liberate NOx (Singh et al, 1986). Investigating formation of PAN is an important part of understanding the formation of photochemical smog and assessing its impacts on human health and atmospheric chemistry
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