Reply on RC2

Abstract

Gaseous pollutants at the ground level seriously threaten the urban air quality environment and public health. There are few estimates of gaseous pollutants that are spatially and temporally resolved and continuous over long periods in China. This study takes advantage of big data and artificial intelligence technologies to generate seamless daily maps of three major pollutant gases, i.e., NO2, SO2, and CO, across China from 2013 to 2020 at a uniform spatial resolution of 10 km. Cross-validation illustrated a high data quality on a daily basis for NO2, SO2, and CO, with mean out-of-bag coefficients of determination (root-mean-square errors) of 0.84 (7.99 μg/m3), 0.84 (10.7 μg/m3), and 0.80 (0.29 mg/m3), respectively. They have experienced significant declines and then recoveries during and after the COVID-19 lockdown associated with changes in anthropogenic emissions in eastern China, while surface CO recovered faster than SO2 and NO2. All gaseous pollutants decreased significantly by 0.23, 2.01, and 49 μg/m3 per year (p < 0.001) across China during 2013–2020, especially in three urban agglomerations. The declining rates were larger during 2013–2017 but slowed down in recent years. Both the areas and occurrence probabilities of days exceeding air quality standards also gradually shrank and weakened over time, especially for SO2 and CO, which almost disappeared during 2018–2020, suggesting significant improvements in air quality in China. This reconstructed dataset of surface gaseous pollutants, i.e., ChinaHighNO2, ChinaHighSO2, and ChinaHighCO, will benefit future (especially short-term) air pollution and environmental health-related studies.