Measurement Report: Aircraft Observations of Ozone, Nitrogen Oxides, and Volatile Organic Compounds over Hebei Province, China

Abstract. To provide insight into the planetary boundary layer (PBL) production of ozone (O3) 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 O3, nitrogen oxides (NOx), carbon monoxide (CO), and volatile organic compounds (VOCs) and relate to rates of O3 production. This analysis shows measured O3 levels ranged from 52 to 142 ppbv, with the peak median concentration (~ 94 ppbv) occurring between 1000 and 1500 m. The NOx concentrations exhibited strong spatial and altitudinal variations, ranging from 0.15 to 49 ppbv. Ratios of CO / NOy and CO / CO2 indicate the prevalence of low efficiency combustion from biomass burning and residential coal burning. Concentrations of total measured VOCs from 26 whole air canisters reveals alkanes dominate the total measured volume mixing ratio of VOCs (68 %) and we see evidence of vehicular emissions, fuel and solvent evaporation, and biomass burning sources. 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 O3 in this region. In the PBL below 500 m, box model calculations constrained by measured precursors indicate the peak rate of mean O3 production was ~ 7 ppbv/hour. Pollution frequently extended above the PBL into the lower free troposphere around 3000 m, where NO2 mixing ratios (~ 400 pptv) led to net production rates of O3 up to ~ 3 ppbv/hour; this pollution can travel substantial distances downwind. The O3 sensitivity regime is determined to be NOx-limited throughout the PBL, while more VOC-limited at low altitudes near urban centres, demonstrating both VOCs and NOx need further control to reduce aloft O3 over Hebei.