Intermediate-Volatility Organic Compounds in Two Chinese Megacities: Sources and Implications for Ozone Formation

]]-Intermediate-volatility organic compounds (IVOCs) are important precursors of ozone and secondary organic aerosol (SOA), yet their urban characteristics and impacts remain insufficiently understood. In this study, IVOCs were investigated during the summer of 2024 in Shenzhen and Beijing, representing southern and northern Chinese megacities, respectively. Beijing exhibited significantly higher average IVOCs concentrations (40.42 ± 30.11 μg/m³) than Shenzhen (6.22 ± 4.50 μg/m³), with residual UCM dominating in both cities. Source apportionment showed that diesel-related emissions were the primary IVOCs source in Shenzhen (44.4%), followed by biomass burning (29.8%), ship emissions (16.7%), and gasoline vehicles (9.1%). In contrast, Beijing's IVOCs were mainly from the petrochemical industry (35.5%), gasoline vehicles (31.5%), and diesel vehicles (25.0%), with minor contributions from biomass/coal combustion (8.1%). PAHs, particularly fluorene, acenaphthylene, and acenaphthene, contributed substantially to IVOCs-related ozone formation potential (OFP). While VOCs accounted for the majority of OFP, IVOCs contributed 32.9% in Shenzhen and 22.1% in Beijing, underscoring their non-negligible role in urban ozone formation. These findings highlight the diverse sources and substantial photochemical reactivity of IVOCs in different urban settings. The results underscore the need to incorporate IVOCs, particularly PAHs, into air quality management and ozone mitigation strategies in similar rapidly urbanizing regions.