Jiawei Xu, Sijia Lou, Nan Wang, Lian Xue, Xin Huang, Aijun Ding

Biogenic volatile organic compounds are vital precursors of tropospheric ozone (O3). In the past decades, northern China has witnessed the strongest enhancement of vegetation covers due to national afforestation projects; however, response of the vegetation greenness to near-surface O3 remains unclear. By integrating measurements and numerical simulations, here we show that O3 pollution in northern China has been enhanced by the unwind greening over the past two decades and will be exacerbated further in this century as the climate warming. We found that isoprene emission increased by 30% over northwestern China because of the vegetation increase and regional warming. Together with changes in anthropogenic emissions, it caused more O3 pollution in city clusters in northern China. In the context of carbon peaking and carbon neutrality policy, vegetation greening will cause aggravating O3 pollution by the middle of this century, which need to be considered in future air quality measures in China.