Anthropogenic drivers of 2013–2017 trends in summer surface ozone in China

TLDR

China’s aggressive air‑pollution controls since 2013 have sharply cut PM2.5, yet surface ozone levels have not declined. The study proposes that future ozone reductions will require combined NOx and VOC controls to offset the ozone‑producing effect of declining PM2.5. After accounting for meteorology, surface ozone has risen in Chinese megacities, especially Beijing and Shanghai, and the trend is mainly driven by reduced PM2.5, which slows hydroperoxy radical loss and accelerates ozone production, rather than changes in NOx or VOC emissions.

Abstract

Significance Drastic air pollution control in China since 2013 has achieved sharp decreases in fine particulate matter (PM 2.5 ), but ozone pollution has not improved. After removing the effect of meteorological variability, we find that surface ozone has increased in megacity clusters of China, notably Beijing and Shanghai. The increasing trend cannot be simply explained by changes in anthropogenic precursor [NO x and volatile organic compound (VOC)] emissions, particularly in North China Plain (NCP). The most important cause of the increasing ozone in NCP appears to be the decrease in PM 2.5 , slowing down the sink of hydroperoxy radicals and thus speeding up ozone production. Decreasing ozone in the future will require a combination of NO x and VOC emission controls to overcome the effect of decreasing PM 2.5 .