Volatile organic compounds in Chengdu: Functional zone disparities and four-year dynamics in a basin city of Southwest China

Summer ozone pollution has become an increasingly important environmental issue in Chengdu, yet systematic evidence on how volatile organic compound (VOC) pollution varies among explicitly defined urban functional areas remains limited. This study analyzed 772 offline VOC samples collected from 19 sites during the summers of 2022-2025. VOC concentrations, chemical composition, source contributions, and ozone formation potential (OFP) were compared among functional areas, while cross-year changes in concentration levels were examined at selected representative sites. VOC concentrations showed pronounced functional-area disparities, with the highest level observed in industrial areas (IA, 327.44 ± 25.08 μg/m3) and the lowest in ecological and green areas (EGA, 159.34 ± 13.72 μg/m3). Summer VOC composition exhibited substantial functional-area heterogeneity. IA had relatively high alkane (32.83%) and alkene/alkyne (23.24%) fractions, ERA had the largest OVOC contribution (43.43%), and EGA showed prominent isoprene contributions. At selected sites, VOC concentrations varied non-monotonically across the four summers, with lower levels in 2023 than in 2022 and subsequent increases at some sites. Positive matrix factorization identified five major VOC sources: Vehicular emissions, industrial emissions, biogenic emissions, combustion, and gasoline evaporation. Vehicular emissions contributed the largest share overall, while industrial emissions were the dominant source in IA (44.39%) and biogenic emissions were most important in EGA (37.42%). OFP suggests that reactive alkenes should be prioritized in IA, OVOCs and their precursors in densely populated areas, and biogenic-anthropogenic photochemical interactions in EGA. By integrating a multi-site network with an explicit functional-area framework, this study provides evidence for reactivity-oriented, function-specific VOC control in Chengdu.