Seasonal discrepancies in peroxyacetyl nitrate (PAN) and its correlation with ozone and PM2.5: Effects of regional transport from circumjacent industrial cities

Peroxyacetyl nitrate (PAN) is the most important reservoir of nitrogen oxides, with effects on atmospheric oxidation capacity and regional nitrogen distribution. The first yearlong observational study of PAN was conducted from September 2018 to August 2019 at a suburban site and an urban site in Zhengzhou, Henan Province, central China. Compared with studies over the past two decades, summer PAN pollution at the suburban site and winter PAN pollution at both sites were more significant, with annual average concentrations of 1.96 +/- 1.44 and 2.01 +/- 1.59 ppbv, respectively. Seasonal PAN discrepancies between the urban and suburban areas were analyzed in detail. Active PAN formation, regional transport, photochemical precursors, and PAN lifetime played key roles during seasons with elevated PAN (winter and spring). According to the results of cluster analysis and potential source contribution function analysis, during the cold months, short-distance air mass transport from the east, south, and southeast of Henan Province and southern Hebei Province increased PAN pollution in urban Zhengzhou. PAN source areas were located in circumjacent industrial cities surrounding Zhengzhou except in the northeastern direction. Based on the relationships between pollutant concentrations, wind speed, and wind direction, a strong positive correlation between PAN and PM2.5 (and O-3) existed in winter due to their joint transport. A slow-moving, low-height air mass passed through surrounding industrial cities before reaching the study area, carrying both pollutants and leading to strong consistency between PAN and O-3 levels. The long-term PAN characteristics described in this study will help clarify the causes of regional air pollution in inland city agglomerations. Moreover, the PAN correlations and joint transport of PAN and PM2.5 (or O-3) support the use of PAN as an indicator of air pollution introduced from surrounding industrial areas. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

Peroxyacetyl nitrate (PAN) serves as a significant reservoir of nitrogen oxides that influences atmospheric oxidation capacity and regional nitrogen distribution. This study identified notable differences in PAN pollution between urban and suburban areas in Zhengzhou, central China, with higher levels observed during winter and spring. Analysis showed that the main sources of PAN pollution during colder months were short-distance air mass transport from specific regions in Henan and Hebei provinces, leading to a strong correlation between PAN and PM2.5 (and O-3) due to joint transport.