PNNL

Abstract

Ozone pollution is one of the most severe air quality issues in China that poses a serious threat to human health and ecosystems. During 2019-2021, the maximum daily 8-hour average O3 concentrations in eastern China (110-122.5°E, 26-42°N) and the rest of China (ROC) show different decreasing patterns, with O3 concentrations in eastern China decreasing by 14.9 µg/m3, which is much larger than 4.8 µg/m3 in ROC. Here, based on the atmospheric chemical transport model (GEOS-Chem) simulations and the machine learning (ML) model (LightGBM) predictions, the reasons for the differences in O3 changes between eastern China and ROC during the warm season (April to September) are investigated. Changes in the meteorological conditions contributed to an ozone decrease by 7.3 (6.8) µg/m3 in eastern China and 6.8 (7.0) µg/m3 in ROC, according to the GEOS-Chem (LightGBM) results, which can be explained by the decrease in chemical production and weakened horizontal and vertical advection. With the influence of meteorological factors excluded, the observations show that changes in anthropogenic emissions resulted in an ozone decrease by 7.6 (8.1) µg/m3 in eastern China and an ozone increase by 2.0 (2.2) µg/m3 in ROC, which is primarily induced by the changes in NOx emissions. The surface measurements and satellite retrievals also indicate that the reduction in NOx emission in ROC is less efficient than that in the more developed eastern China, leading to contrasting changes in ozone concentrations between eastern China and ROC during 2019–2021. Our results highlight the critical need to reduce ozone precursor emissions in the rest regions of China apart from eastern China.