Fine particulate matter (PM2.5) trends in China, 2013-2018: separating contributions from anthropogenic emissions and meteorology

Fine particulate matter (PM_2.5) is a severe air pollution problem in China. Observations of PM_2.5 have been available since 2013 from a large network operated by the China National Environmental Monitoring Center (CNEMC). The data show a general 30 %-50 % decrease in annual mean PM_2.5 across China over the 2013-2018 period, averaging at -5.2 µg m^-3 a^-1. Trends in the five megacity cluster regions targeted by the government for air quality control are -9.3±1.8 µg m^-3 a^-1 (±95 % confidence interval) for Beijing-Tianjin-Hebei, -6.1±1.1 µg m^-3 a^-1 for the Yangtze River Delta, -2.7±0.8 µg m^-3 a^-1 for the Pearl River Delta, -6.7±1.3 µg m^-3 a^-1 for the Sichuan Basin, and -6.5±2.5 µg m^-3 a^-1 for the Fenwei Plain (Xi'an). Concurrent 2013-2018 observations of sulfur dioxide (SO₂) and carbon monoxide (CO) show that the declines in PM_2.5 are qualitatively consistent with drastic controls of emissions from coal combustion. However, there is also a large meteorologically driven interannual variability in PM_2.5 that complicates trend attribution. We used a stepwise multiple linear regression (MLR) model to quantify this meteorological contribution to the PM_2.5 trends across China. The MLR model correlates the 10 d PM_2.5 anomalies to wind speed, precipitation, relative humidity, temperature, and 850 hPa meridional wind velocity (V850). The meteorology-corrected PM_2.5 trends after removal of the MLR meteorological contribution can be viewed as being driven by trends in anthropogenic emissions. The mean PM_2.5 decrease across China is -4.6 µg m^-3 a^-1 in the meteorology-corrected data, 12 % weaker than in the original data, meaning that 12 % of the PM_2.5 decrease in the original data is attributable to meteorology. The trends in the meteorology-corrected data for the five megacity clusters are -8.0±1.1 µg m^-3 a^-1 for Beijing-Tianjin-Hebei (14 % weaker than in the original data), -6.3±0.9 µg m^-3 a^-1 for the Yangtze River Delta (3 % stronger), -2.2±0.5 µg m^-3 a^-1 for the Pearl River Delta (19 % weaker), -4.9±0.9 µg m^-3 a^-1 for the Sichuan Basin (27 % weaker), and -5.0±1.9 µg m^-3 a^-1 for the Fenwei Plain (Xi'an; 23 % weaker); 2015-2017 observations of flattening PM_2.5 in the Pearl River Delta and increases in the Fenwei Plain can be attributed to meteorology rather than to relaxation of emission controls.