Spatial Characteristics, Sources of Volatile Organic Compounds and Effects on O3 Formation in Summer in Taiyuan, China.

Many previous studies on volatile organic compounds (VOCs) have focused on Photochemical Assessment Monitoring Station (PAMS) VOCs at a single site, yet there is limited understanding of the spatial heterogeneity of both PAMS VOCs and oxygenated VOCs (OVOCs) across multiple functional zones at the city scale. To better understand the characteristics, sources and the effects of VOCs on O3, we conducted simultaneous measurements of 71 VOCs (57 PAMS VOCs and 14 OVOCs) at three urban sites (Taoyuan, TY; Jinyuan, JY; Xiaodian, XD) and one suburban site (Shanglan, SL) in Taiyuan, a heavily industrialized city in northern China, during the summertime of 2022 and 2023. Total VOCs (TVOCs) concentrations were comparable at SL (21.9 ± 7.7 ppbv) and JY (21.9 ± 8.7 ppbv), but higher than those at TY (20.3 ± 6.3 ppbv) and XD (19.5 ± 6.4 ppbv). OVOCs were the dominant component at all sites, accounting for over 60% of TVOCs, with formaldehyde as the most abundant species. Ozone formation potential (OFP) followed the order of SL (119.6 ± 47.7 ppbv) > JY (112.0 ± 58.2 ppbv) > TY (100.4 ± 34.2 ppbv) > XD (97.1 ± 34.1 ppbv), with OVOCs contributing over 75% to the total OFP. Positive matrix factorization (PMF) resolved seven sources, with secondary formation as the largest contributor at all sites (24.6-32.5% of TVOCs, 30.5-37.0% of OFP). The second-largest source of VOCs and OFP exhibited a systematic spatial gradient: biogenic sources at SL (22.0%, 28.9%), gasoline vehicle exhausts at TY (22.5%, 21.8%), coking sources at JY (23.9%, 22.8%), and combustion sources at XD (23.6%, 26.0%). The lack of OVOCs could lead to an overestimation of primary sources and an underestimation of photochemical processing in source apportionment studies. These findings demonstrate that zone-specific measures should be complemented by regional precursor reductions for effective O3 mitigation in Taiyuan.