Measurement report: Aircraft observations of ozone, nitrogen oxides, and volatile organic compounds over Hebei Province, China

To provide insight into the planetary boundary layer (PBL) production of ozone (O-3) over the North China Plain, the Air chemistry Research in Asia (ARIAs) campaign conducted aircraft measurements of air pollutants over Hebei Province, China, between May and June 2016. We evaluate vertical profiles of trace gas species including O-3, nitrogen oxides (NOx), carbon monoxide (CO), and volatile organic compounds (VOCs) and relate to rates of O-3 production. This analysis shows measured O-3 levels ranged from 45 to 146 ppbv, with the peak median concentration (similar to 92 ppbv) occurring between 1000 and 1500 m. The NOx concentrations exhibited strong spatial and attitudinal variations, with a maximum of 53 ppbv. Ratios of CO/CO2 indicate the prevalence of low-efficiency combustion from biomass burning and residential coal burning but indicate some success of regional pollution controls compared to earlier studies in China. Concentrations of total measured VOCs reveal alkanes dominate the total measured volume mixing ratio of VOCs (68 %), and sources include vehicular emissions, fuel and solvent evaporation, and biomass burning. Alkanes and alkenes/alkynes are responsible for 74 % of the total VOC reactivity assessed by calculating the OH loss rates, while aromatics contribute the most to the total ozone formation potential (OFP) (43 %) with toluene, m/p-xylene, ethylene, propylene, and i -pentane playing significant roles in the aloft production of O-3 in this region. In the PBL below 500 m, box model calculations constrained by measured precursors indicate the peak rate of mean O-3 production was similar to 7 ppbv h(-1). Pollution frequently extended above the PBL into the lower free troposphere around 3000 m, where NO2 mixing ratios (similar to 400 pptv) led to net production rates of O-3 up to similar to 3 ppbvh(-1); this pollution can travel substantial distances downwind. The O-3 sensitivity regime is determined to be NOx-limited throughout the PBL, whereas it is more VOC-limited at low altitudes near urban centers, demonstrating that control of both VOCs and NOx is needed to reduce aloft O-3 pollution over Hebei.