Air quality improvement in response to intensified control strategies in Beijing during 2013-2019.

Beijing's air pollution has become of increasing concern in recent years. The central and municipal governments have issued a series of laws, regulations, and strategies to improve ambient air quality. The "Clean Air Action" issued in 2013 and the "Comprehensive Action" issued in 2017 largely addressed this concern. In this study, we assessed the effectiveness of the two action plans by environmental monitoring data and evaluated the influencing factors including meteorology, pollutant emissions, and energy structure. The spatial distributions of air pollutants were analyzed using the Kriging interpolation method. The Principal Component Analysis-Multiple Nonlinear Regression (PCA-MNLR) model was applied to estimate the effects of meteorological factors. The results have shown that Beijing's air quality had a measurable improvement over 2013-2019. "Good air quality" days had the highest increases, and "hazardous air quality" days had the most decreases. SO decreased most, followed by CO, PM, PM, and NO in descending order, but O showed a fluctuant increase. The "Comprehensive Action" was more effective than the "Clean Air Action" in reducing heavy pollution days during the heating period. The meteorological normalized values of the main pollutants were lower than the observation data during 2013-2016. However, the observed values became lower than the normalized values after 2017, which indicated beneficial weather conditions in 2017 and afterwards. The emissions of SO and dust significantly decreased while NOx had a slight decrease, and the energy structure changed with a dramatic decrease in coal consumption and an obvious increase in the use of natural gas and electricity. The significant reduction of coal-fired emissions played a dominant role in improving Beijing's air quality, and vehicle emission control should be further enhanced. The results demonstrated the effectiveness of the two action plans and the experience in Beijing should have potential implications for other areas and nations suffering from severe air pollution.