Observation of VOCs in Winter and the Difference from Actual Emissions: Photochemical Loss Correction and Health Economic Loss Assessment.

Abstract

Ground-level ozone (O3) pollution remains a critical air quality challenge in China, with volatile organic compounds (VOCs) serving as key precursors. However, the photochemical loss of VOCs during atmospheric transport introduces substantial biases in source apportionment and O3 formation potential (OFP) assessments, particularly in winter when such losses are often overlooked. This study conducted online monitoring of 103 VOC species at hourly resolution in Huangshi City, a typical old industrial base in central China, during January 2025. By integrating photochemical age-based loss correction, positive matrix factorization (PMF) source apportionment, OFP evaluation, and health-economic loss assessment, this study systematically quantified the impacts of photochemical consumption on source contributions, O3 formation, and associated health burdens. Results showed that the mean TVOC concentration was 27.71 ppbv, with alkanes dominating the mass fraction (48.38%), while alkenes and aromatics were the primary drivers of photochemical loss. Photochemical loss OFP (PLOFP) correction revealed that observed concentrations underestimated the true OFP by 62.34% ± 26.67%, with isoprene, trans-2-butene, and m/p-xylene as the key contributing species. PMF analysis identified six emission sources; after correction, vehicle exhaust (+3.78%) and biogenic sources (-1.36%) showed significantly increased contributions, with vehicle exhaust replacing solvent use as the largest mass contributor. Notably, biogenic VOCs, despite accounting for <5% of the mass, contributed over 20% of PLOFP, with >70% of them photochemically consumed. O3 exposure was estimated to cause 42 all-cause excess deaths and 1.34 billion Yuan in economic losses (5.82‰ of GDP), of which 47.62% was attributed to photochemical loss conversion. These findings demonstrate that photochemical loss correction was indispensable for accurate source apportionment and health risk evaluation, and that wintertime O3 pollution control in industrial cities should prioritize highly reactive species and adopt reactivity-oriented, health-based strategies.