Characteristics and sources of VOCs in a coastal city in eastern China and the implications in secondary organic aerosol and O3 formation

Abstract

Volatile organic compounds (VOCs) play an essential role in the formation of secondary organic aerosol (SOA) and O3. However, our understanding of the characteristics and sources of VOCs in coastal cities is still limited. Here we conducted one-year measurements of VOCs during 2021–2022 in a coastal city in eastern China using Gas Chromatography-Mass Spectrometry. Our results showed strong seasonal variations in total VOCs (TVOCs) with the highest concentrations in winter (28.5 ± 15.1 ppbv) and the lowest values in autumn (14.5 ± 7.6 ppbv). Alkanes dominated the TVOCs during all seasons, on average accounting for 36.2 %–50.2 %, while the contributions of aromatics (5.5 %–9.3 %) were ubiquitously lower than those in other megacities in China. Aromatics exhibited the largest contribution to SOA formation potential (77.6 %–85.5 %) during all seasons, while alkenes (30.9 %–41.1 %) and aromatics (20.6 %–33.2 %) were the dominant contributors to ozone formation potential, and the O3 formation is “VOC-limited” in summer in the city. Particularly, we found that the estimated SOA yield only explained 9.4 %–16.3 % of the observed SOA, suggesting a significant absence of semi-volatile and intermediate-volatile organic compounds. Positive matrix factorization demonstrated that industrial production and fuel combustion were the main sources of VOCs especially in winter (24 % and 31 %), while secondary formation was dominant in summer and autumn (37 % and 28 %). Comparatively, the sources of liquefied petroleum gas and vehicular exhaust were also important, yet did not show strong seasonal variations. Potential source contribution function further highlighted a great challenge for VOCs control in autumn and winter because of the large influences of regional transport.