Diagnosing year-round ozone-relevant VOC reactivity under meteorological constraints in urban Beijing

Abstract

Abstract Static volatile organic compound (VOC) rankings can identify abundant or reactive compounds, but their ozone relevance depends on the meteorological and photochemical state during ozone production. Here we combine yearlong hourly observations of speciated VOCs in urban Beijing in 2022 with measured NO 2 photolysis frequency, routine pollutants and ERA5 meteorology to diagnose ozone-relevant VOC reactivity under meteorological constraints. Annual mean total VOC abundance (TVOC), VOC OH loss rate (L OH ) and maximum incremental reactivity weighted ozone formation potential (OFP) were 21.70 ppbv, 2.22 s −1 and 89.6 µg m − 3 O 3 , respectively. Alkanes dominated TVOC, whereas oxygenated VOCs contributed disproportionately to L OH and OFP. Annual high-O3 days were associated with stronger photolysis, lower NO 2 , enhanced oxygenated VOCs and higher L OH , but not with robust increases in TVOC or total OFP. Random forest models showed that temporal structure, meteorology, and photochemistry captured most predictable O 3 variability. Group-level VOC abundance added a modest diagnostic increment, whereas total L OH and OFP added little independent information. A species diagnostic matrix identified acetaldehyde and propanal as stable multi-evidence signals. This framework provides a meteorology-conditioned observational screen for identifying VOC markers and episodes associated with high-O 3 conditions, rather than a direct emissions-control or VOC/NO x sensitivity ranking.