Constructing a spatiotemporally coherent long-term PM2.5 concentration dataset over China during 1980-2019 using a machine learning approach

The lack of long-term observations and satellite retrievals of health-damaging fine particulate matter in China has demanded the estimates of historical PM2.5 (particulate matter less than 2.5 mu m in diameter) concentrations. This study constructs a gridded near-surface PM2.5 concentration dataset across China covering 1980-2019 using the space-time randomforest model with atmospheric visibility observations and other auxiliary data. Themodeled daily PM2.5 concentrations are in excellent agreementwith groundmeasurements, with a coefficient of determination of 0.95 and mean relative error of 12%. Besides the atmospheric visibility which explains 30% of total importance of variables in the model, emissions and meteorological conditions are also key factors affecting PM2.5 predictions. From 1980 to 2014, the model-predicted PM2.5 concentrations increased constantly with the maximum growth rate of 5-10 mu g/m(3)/decade over eastern China. Due to the clean air actions, PM2.5 concentrations have decreased effectively at a rate over 50 mu g/m(3)/decade in the North China Plain and 20-50 mu g/m(3)/decade over many regions of China during 2014-2019. The newly generated dataset of 1-degree gridded PM2.5 concentrations for the past 40 years across China provides a useful means for investigating interannual and decadal environmental and climate impacts related to aerosols. (C) 2020 Elsevier B.V. All rights reserved.