Reconstruction of PM2.5 Concentrations in East Asia on the Basis of a Wide–Deep Ensemble Machine Learning Framework and Estimation of the Potential Exposure Level from 1981 to 2020

Abstract

Satellite observations are widely used to estimate the concentrations of surface air pollutants, but the temporal coverage of these datasets is relatively short. To overcome this limitation, we propose a wide–deep ensemble machine learning framework to reconstruct the fine particulate matter (PM2.5) dataset of east Asia (EA) over the past four decades (1981–2020). The results indicate that the framework effectively leveraged the advantages of satellite observations (higher accuracy) and model-based estimations (longer temporal coverage) of surface air pollutants. The reconstructed PM2.5 concentrations agreed well with the ground measurements, with coefficient of determination (R2) and root-mean-square error (RMSE) values of 0.99 and 1.38 μg·m−3, respectively, which outperformed the satellite-based PM2.5 estimates. As more ground measurements were incorporated into the model for training, the average RMSE in Japan and the Korean Peninsula decreased to 0.83 and 1.50 μg·m−3, respectively. Simultaneously, on the basis of the reconstructed datasets, we investigated the exposure level to PM2.5 in EA from 1981 to 2020. Since 2000, the increase in anthropogenic emissions has substantially worsened the air quality in EA, and nearly 50% of the population resided in areas where the annual average PM2.5 concentrations exceeded 50 μg·m−3 from 2009–2010. Despite the implementation of various mitigation strategies by local authorities to lower the ambient PM2.5 concentrations, the entire exposure level in EA is still implausible to meet the WHO air quality guidelines. In addition, population aging and climate change have the potential to increase PM2.5 exposure risk in the future. For policy-makers in EA, it is essential to consider the effects of these factors and develop more effective mitigation strategies that aim to lessen the health impact associated with PM2.5 exposure.