Abstract. Oil and natural gas (O&NG) exploration presents a significant source of atmospheric volatile organic compounds (VOCs), which are central players of tropospheric chemistry and contribute to formations of ozone (O3) and secondary organic aerosols. The impacts of O&NG extraction on regional air quality have been investigated in recent years in North America, but have long been overlooked in China. To assess the impacts of O&NG exploration on tropospheric O3 and regional air

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... ality in China, intensive field observations were conducted during February–March and June–July 2017 in the Yellow River delta, an oil extraction region in northern China. Very high concentrations of ambient VOCs were observed at a rural site, with the highest alkane mixing ratios reaching 2498 ppbv. High-O3 episodes were not encountered during wintertime but were frequently observed in summer. The emission profiles of VOCs from the oil fields were directly measured for the first time in China. The chemical budgets of ROx radicals and O3 were dissected with a detailed chemical box model constrained by in situ observations. The highly abundant VOCs facilitated strong atmospheric oxidation capacity and O3 formation in the region. Oxygenated VOCs (OVOCs) played an essential role in the ROx primary production, OH loss, and radical recycling. Photolysis of OVOCs, O3, and HONO as well as ozonolysis reactions of unsaturated VOCs were major primary sources of ROx. NOx was the limiting factor of radical recycling and O3 formation. This study underlines the important impacts of O&NG extraction on atmospheric chemistry and regional air quality in China.