Role of Organic Vapor Precursors in Secondary Organic Aerosol Formation: Concurrent Observations of IVOCs and VOCs in Guangzhou.

Secondary organic aerosol (SOA) formed through the atmospheric transformation of organic vapors constitutes a significant portion of fine particulate matter or PM2.5. While recent laboratory studies underscore the importance of intermediate‐volatility organic compounds (IVOCs) as key precursors to SOA, field observations that recognize the role of both volatile organic compounds (VOCs) and IVOCs in SOA formation remain scarce. In this study, we conducted concurrent measurements of VOCs and IVOCs in ambient air at urban and suburban sites in Guangzhou during a PM2.5 pollution event in winter 2021. The results reveal that between 12:00–15:00 local time, the photochemically adjusted initial concentrations of VOCs at both sites were approximately 7 times higher than that of IVOCs. However, the SOA formation potential (SOAFP) of primary hydrocarbon IVOCs exceeded that of VOCs by over 3–4 times. Receptor modeling results further indicated that while ship emissions contributed to less than 10% of the C2–C22 primary hydrocarbons concentration (VOCs + primary carbonaceous IVOCs), they accounted for the most significant source (approximately 40%) of SOA formation. This study highlights the substantial role of IVOCs in SOA formation and emphasizes the importance of future PM2.5 pollution control measures targeting major IVOCs contributors, such as ship emissions in harbor cities. Plain Language Summary: Fine particulate matter (PM2.5) is a critical air pollutant affecting human health, with secondary organic aerosol (SOA) being a significant component. This study investigated the formation of SOA by examining both volatile organic compounds (VOCs) and intermediate‐volatility organic compounds (IVOCs) in Guangzhou during a pollution event. Despite VOCs being more abundant, IVOCs showed higher potential to form SOA. Surprisingly, ship emissions, though minor in contributing to C2–C22 primary hydrocarbons, played a major role in SOA formation. This highlights the need to control IVOCs, especially from ships, to combat PM2.5 pollution, particularly in coastal cities. Key Points: Concurrent observations of volatile organic compounds (VOCs) and intermediate‐volatility organic compounds (IVOCs) were conducted during a PM2.5 pollution event in GuangzhouVOC concentrations were ∼7 times that of hydrocarbon IVOCs, but their secondary organic aerosol (SOA) formation potentials were less than half that of hydrocarbon IVOCsShip emissions contributed less than 10% of total VOCs and IVOCs, but could account for up to 40% of SOA formation [ABSTRACT FROM AUTHOR]