Daytime Ozone Production Determined by Ratios of Total Volatile Organic Compound Consumption to Nitrogen Oxide Concentrations

Abstract

To reduce the uncertainty in analyzing ozone (O₃) sensitivities based on observed concentrations of volatile organic compounds (VOCs) and nitrogen dioxide, this study proposed the application of consumed VOC concentrations to establish their nonlinear relationship in the actual atmosphere. These parameters were calculated based on the reaction rates and online observations of VOCs, nitrogen dioxide, and O₃ concentrations at Deyang, Chengdu, and Meishan in the Chengdu Plain, China, during summer 2019. The nighttime isoprene consumption was maximum at 2.03 ppbv at Meishan. The daytime acetaldehyde consumption was a maximum at 2.68 ppbv at Deyang, possibly due to its higher primary emissions and secondary production and its consumption by both OH radicals and photolysis. When the ratios of the total consumed VOC concentrations to the observed or initial NO_x (NO_x = NO + NO₂) concentrations were 3.51 ppbv ppbv^–1 or 2.22 ppbv ppbv^–1, daytime O₃ variations reached a maximum of 8.45 ppbv or 7.52 ppbv, respectively. The ratios delineated the VOC-sensitive and NO_x-sensitive areas. Over 98% of hourly data were in VOC-sensitive areas at both Chengdu and Meishan, respectively, while over 14% of hourly data belonged to NO_x-sensitive areas at Deyang. This provided a more accurate method for assessing real-time O₃ sensitivity and thus implementing dynamic hierarchical control strategies.