Increased night-time oxidation over China despite widespread decrease across the globe

Nitrogen oxides (NO x = NO + NO 2 ) emitted from combustion and natural sources are reactive gases that regulate the composition of Earth’s atmosphere. Nocturnal oxidation driven by nitrate radicals is an important but poorly understood process in atmospheric chemistry, affecting the lifetimes of NO x and ozone and particulate pollution levels. Understanding the trends of nitrate radicals is important to formulating effective pollution mitigation strategies and understanding the influence of NO x on climate. Here we analyse publicly available monitoring data on NO x and ozone to assess production rates and trends of surface nitrate radicals from 2014 to 2021 across the globe. We show that nitrate radicals have undergone strong increases in China during 2014–2019 but exhibited modest decreases in the United States and the European Union. Accelerated night-time oxidation has shortened the lifetime of summer NO x in China by 30% during 2014–2019. This change will strongly affect ozone formation and has policy implications for the joint control of ozone and fine particulate pollution.