Abstract. Fine particulate matter (PM2.5) is a severe air pollution problem in China. Observations of PM2.5 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 of annual mean PM2.5 across China over the 2013–2018 period, averaging 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 Yangtze River Delta, 2.7 ± 0.8 μg m−3 a−1 for Pearl River Delta, 6.7 ± 1.3 μg m−3 a−1 for Sichuan Basin, and 6.5 ± 2.5 μg m−3 a−1 for Fenwei Plain (Xi'an). Concurrent 2013–2018 observations of sulfur dioxide (SO2) and CO show that the declines in PM2.5 are qualitatively consistent with drastic controls of emissions from coal combustion. However, there is also a large meteorologically driven interannual variability of PM2.5 that complicates trend attribution. We used a stepwise multiple linear regression (MLR) model to quantify this meteorological contribution to the PM2.5 trends across China. The MLR model correlates the 10-day PM2.5 anomalies to wind speed, precipitation, relative humidity, temperature, and 850 hPa meridional wind velocity (V850). We find that meteorology made a minor but significant contribution to the observed 2013–2018 PM2.5 trends across China and that removing this influence reduces the uncertainty on the emission-driven trends. The mean PM2.5 decrease across China is 4.6 μg m−3 a−1 in the meteorology-corrected data, 12 % weaker than in the original data. The residual trends in the five megacity clusters attributable to changes in anthropogenic emission are 8.0 ± 1.1 μg m−3 a−1 for Beijing-Tianjin-Hebei (14 % weaker than the observed trend), 6.3 ± 0.9 μg m−3 a−1 for Yangtze River Delta (3 % stronger), 2.2 ± 0.5 μg m−3 a−1 for Pearl River Delta (19 % weaker), 4.9 ± 0.9 μg m−3 a−1 for Sichuan Basin (27 % weaker), and 4.9 ± 1.9 μg m−3 a−1 for Fenwei Plain (Xi'an; 25 % weaker). 2015–2017 observations of flattening PM2.5 in the Pearl River Delta, and increase in the Fenwei Plain, can be attributed to meteorology rather than to relaxation of emission controls.
Review of Sun et al. “Two years online measurement of fine particulate nitrate in western Yangtze River Delta: Influences of thermodynamics and N2O5 hydrolysis”
