Significant influence of oxygenated volatile organic compounds on atmospheric chemistry: A case study in a typical industrial city in China

Oxygenated volatile organic compounds (OVOCs), an important subgroup of volatile organic compounds (VOCs), are emitted directly or formed secondarily through photochemical processes. They play a crucial role in tropospheric chemistry as ozone (O3) precursors. However, due to measurement limitations, the influence of OVOCs on O3 formation has often been underestimated. In this study, 74 VOCs (including 18 OVOCs) were measured at five representative stations (urban, suburban, industrial, upwind, and downwind stations) in Zibo, an industrial city in the North China Plain. The VOCs level in Zibo (44.6 ± 20.9 × 10-9) is in the upper-middle range (> 32 × 10-9) compared to previous studies conducted in most Chinese cities, with OVOCs contributing for 30.0 %-37.8 %. The average O3 formation potential in Zibo is 410.4 ± 197.2 μg m-3, with OVOCs being the dominant contributor (31.5 %-55.9 %). An observation-based model (OBM) was used to access the contributions of chemical production (RNetProd) and emissions/transport (REmis&Trans) to individual OVOCs. Daytime (08:00-18:00 LT) RNetProd is highest at the urban site (5.9 × 10-9 h-1), while nighttime REmis&Trans is most negative at the industrial site (0.76 × 10-9 h-1). Simulations without OVOC constraint overestimate OVOCs (42.1 %-126.5 %) and key free radicals (e.g., hydroperoxy radicals (HO2, 5.3 %-20.4 %) and organic peroxy radicals (RO2, 6.6 %-35.1 %)), leading to a 1.8 %-11.9 % O3 overestimation. This overestimation causes an underestimation of hydroxyl radicals (OH) (1.8 %-20.9 %) and atmospheric oxidizing capacity (3.5 %-12.5 %). These findings emphasize the importance of comprehensive OVOC measurements to constrain numerical models, especially in regions with dense anthropogenic emissions, to better reproduce atmospheric photochemistry, and to formulate more effective air pollution control strategies.