Future prolonged ozone pollution season over the North China Plain driven by emission reductions and climate change

In 2021, the World Health Organization (WHO) introduced for the first time the standard for the peak season ozone (six-month mean MDA8 ozone) of no more than 60 μg m^-3. Typically, the warm season from April to October is often considered as the peak ozone season. However, the highly polluted North China saw the prolonged ozone pollution season based the national surface network measurement, which is threatening public health and the mitigation of PM2.5 pollution. In order to accurately quantify the risk of this ozone season exposure, here this study proposes some methods to quantitatively characterize the active ozone photochemistry season based on the Ox (NO2+O3) and ozone-temperature relationship. Firstly, we found that the active ozone photochemistry season has extended by about four weeks in the course of fast emission reductions from 2014-2022. Then, combined with atmospheric chemical modeling and future SSP scenarios, it is found that deep emission reductions and climate warming will significantly increase the length of peak ozone season over the North China Plain.