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Peroxyacetyl nitrate (PAN) can effectively indicate photochemical pollution, and also plays a vital role in regional oxidant balance. One-year continuous monitoring of PAN in a coastal city of southeastern China was investigated. The mean concentration of PAN in winter (0.64 ppb) was close to that in autumn (0.73 ppb), indicating that photochemical pollution was still non-negligible in the cold season. The peak occurrence time between O 3 and PAN had a delay of 1-2 h in four seasons, due to the rapid decomposition rate of PAN in midday. Emission sources of the precursors are located to the south of the monitoring site, so high concentrations of PAN and O 3 are frequently observed under southerly wind conditions. The air mass with low concentration of PAN (0.22-0.34 ppb) and O 3 (18.17-23.67 ppb) originated from the ocean with less anthropogenic air pollutants. Continental air mass with high PAN concentration might be related to the contribution of heterogeneous reactions of PM 2.5 to the promotion of PAN formation. In the polluted case, PAN concentration was often higher than 1.0 ppb and reached the peak of 4.2 ppb, suggesting the influence of photochemical reactions and local accumulation. High concentrations of HONO and sufficient ultraviolet radiation might be the main factors for rapid photochemical production of PAN. Besides, the lifetime of PAN in winter under the condition of high PM 2.5 concentration (≥35 μg·m -3 ) was up to 3.246 days. This study provided insights into photochemical mechanism and pollution process in a coastal city of southeastern China., Competing Interests: Declaration of competing interest The authors declare that there is no conflict of financial interest., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Volatile organic compounds (VOCs) are important trace gases in the atmosphere, affecting air quality (e.g. ozone and secondary organic aerosol formation) and human health. To understand the emission, transport and chemistry of VOCs in the southeast of China (Fujian Province), a campaign was conducted in summer and winter of 2016 at three contrasting sites in close proximity. One measurement site (Mt. Wuyi) is a mountainous forest site (1139 m a.s.l.) located in a natural reserve, while the other two sites (Fuzhou, Xiamen) are coastal urban sites with high population and vehicle density. Comparison of VOCs at these three sites provides a valuable perspective on regional air pollution and transport. Many of the measured alkanes, alkenes and aromatics exhibited clear seasonal and diurnal patterns, driven by variations of hydroxyl (OH) radicals, which is the predominant oxidant of VOCs in the atmosphere. By examining tracer-tracer correlations for VOCs, variability-lifetime analysis and 36 h backward trajectories, strong emissions from vehicular exhaust, liquefied petroleum gas (LPG) and solvent usage were identified as key sources in Fuzhou and Xiamen, whereas at Mt. Wuyi the main emission sources were local emissions (e.g. biomass burning) in summer and long-range transport in winter. The results indicate that natural sites could be impacted strongly by surrounding urbanization. Isoprene and propylene in summer and propylene in winter contributed the most to ozone formation at the three sites. The data in this study provides a useful benchmark for future research on air quality monitoring and emission sources in the region., (Copyright © 2018 Elsevier B.V. All rights reserved.)