Two-decade surface ozone (O3) pollution in China: enhanced fine-scale estimations and environmental health implications

Surface ozone (O3) has become a primary pollutant affecting urban air quality and public health in China.To address this concern, we developed a nation-wide surface maximum daily average 8-h (MDA8) O3 concentration dataset for China (ChinaHighO3) at a 10-km resolution since 2013 which has been widely employed in a wide range studies.To meet the increasing demand for its usage, we have made significant enhancements, including the development of a more advanced deep learning model and the incorporation of major source updates, such as 1 km surface downward solar radiation and air temperature directly from satellite retrievals.Additionally, we extend the temporal coverage dating back to 2000, increase the spatial resolution to 1 km, and most importantly, notably improve data quality (with a 5% increase in the cross-validation coefficient of determination and an 11.2% decrease in the root-mean-square error compared to the previous dataset).Using the substantially improved new product, we have analyzed the dataset and found some dynamic and diverse patterns in national surface O3 levels over the past two decades.The annual mean levels have shown relative stability from 2000 to 2015, followed by a sharp increase, reaching peak values in 2019, and subsequently declining.Additionally, we observed a large relative difference of 13% in peak-season surface O3 concentrations between urban and rural regions in China.This disparity has significantly increased since 2015, particularly in the Beijing-Tianjin-Hebei and Pearl River Delta regions.Notably, nearly all population across China (> 99.5%) have resided in areas exposed to surface O3 pollution exceeding the World Health Organization (WHO) recommended long-term air quality guideline (AQG) level [peak-season MDA8 O3 > 60 μg/m 3 ] since 2000.Moreover, the short-term population-risk exposure to daily surface O3 pollution showed a significant increasing trend of 1.19% (p < 0.001) of the days exceeding the WHO's recommended short-term AQG level (daily MDA8 = 100 μg/m 3 ) per year during the 22-year period considered here.The overall upward trend (0.93 ± 0.19 μg/m 3 /yr, p < 0.001) in peak-season surface O3 pollution has led to an exceptionally large rate of increase of 964 (95% confidence interval: 492, 1303) premature deaths per year during 2000-2021 in China.Urgent action is required to develop comprehensive strategies aimed at mitigating surface O3 pollution to enhanced air quality in the future.