Abstract
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 45 to 146 ppbv, with the peak median concentration (∼ 92 ppbv) occurring between 1000 and 1500 m. The NOx concentrations exhibited strong spatial and altitudinal 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 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 h−1. 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 h−1; this pollution can travel substantial distances downwind. The O3 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 O3 pollution over Hebei.
Highlights
Explosive urbanization and rapid industrialization contributed to high ground-level ozone (O3) and particulate matter (PM) over the past several decades in the North China Plain (NCP) (Johnson et al, 2006; Ran et al, 2011; Shao et al, 2009; Zhang et al, 2014)
Benish et al.: Airborne observations of O3 and its precursors over Hebei Province large-scale burning of winter wheat residues in the NCP are some of the many sources responsible for O3 precursors, such as nitrogen oxides (NOx = NO + NO2) and volatile organic compounds (VOCs) (Chen et al, 2017; Long et al, 2016; Stavrakou et al, 2016)
The aircraft was equipped with the following trace gas analyzers: (1) a Picarro cavity ring-down spectrometer (CRDS) for measurements of CH4, CO2, carbon monoxide (CO), and H2O; (2) a Thermal Electron Corporation (TECO) Model 49C UV absorption O3 analyzer; (3) a TECO Model 43C pulsed fluorescence SO2 analyzer; (4) a Los Gatos Research model RMT-200 CRDS NO2 analyzer; and (5) a TECO Model 42C NO-NOy analyzer
Summary
Explosive urbanization and rapid industrialization contributed to high ground-level ozone (O3) and particulate matter (PM) over the past several decades in the North China Plain (NCP) (Johnson et al, 2006; Ran et al, 2011; Shao et al, 2009; Zhang et al, 2014). Several studies using the NASA Ozone Monitoring Instrument (OMI) have found reductions of some pollutants like sulfur dioxide (SO2) over the NCP (He et al, 2012; Krotkov et al, 2016; Li et al, 2010, 2017), but NO2 pollution still remains severe in China (Fig. 1a)
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