Urban–Suburban Differences in Ozone Formation Mechanism and VOC Sources in the Lake Taihu Region, China

Ground-level ozone (O3) pollution has become a major air-quality concern in the Yangtze River Delta, a highly urbanized region with abundant lakes and rivers. However, the mechanisms underlying urban-suburban O3 differences in lakeside regions remain insufficiently understood. In this study, simultaneous observations of O3 and its precursors were conducted at an urban site and a lakeside suburban site in Wuxi, near Lake Taihu, from 1 August to 5 September 2024. Both sites experienced elevated O3 pollution. During specific pollution episodes, however, the suburban site exhibited comparable to or higher O3 concentrations despite lower nitrogen dioxide (NO2) levels. Positive matrix factorization (PMF) analysis revealed stronger anthropogenic influences on volatile organic compounds at the urban site, whereas biogenic emissions and oxidation showed a greater contribution at the suburban site. Observation-based box model results indicated stronger local photochemical O3 production at the suburban site. During lake-breeze episodes, O3 and carbon monoxide (CO) concentrations at the suburban site were significantly higher than those at the urban site, consistent with the influence of lake-breeze recirculation and photochemically processed air masses. Backward-trajectory analysis showed that southeasterly air masses were associated with elevated O3 concentrations and stronger photochemical aging. These findings highlight the importance of considering local precursor chemistry together with lake-induced circulation and regional transport in O3 control strategies for lakeside urban regions.