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Global Multi-resolution Terrain Elevation Data 2010 (GMTED2010)

Regional severe haze represents an enormous environmental problem in China, influencing air quality, human health, ecosystem, weather, and climate. These extremes are characterized by exceedingly high concentrations of fine particulate matter (smaller than 2.5 µm, or PM2.5) and occur with extensive temporal (on a daily, weekly, to monthly timescale) and spatial (over a million square kilometers) coverage. Although significant advances have been made in field measurements, model simulations, and laboratory experiments for fine PM over recent years, the causes for severe haze formation have not yet to be systematically/comprehensively evaluated. This review provides a synthetic synopsis of recent advances in understanding the fundamental mechanisms of severe haze formation in northern China, focusing on emission sources, chemical formation and transformation, and meteorological and climatic conditions. In particular, we highlight the synergetic effects from the interactions between anthropogenic emissions and atmospheric processes. Current challenges and future research directions to improve the understanding of severe haze pollution as well as plausible regulatory implications on a scientific basis are also discussed.

https://www.pnas.org/content/pnas/116/18/8657.full.pdf

Severe haze in northern China: A synergy of anthropogenic emissions and atmospheric processes.

Abstract. Fine particulate matter (PM2.5) is a severe air pollution\nproblem in China. Observations of PM2.5 have been available since 2013\nfrom a large network operated by the China National Environmental Monitoring\nCenter (CNEMC). The data show a general 30 %–50 % decrease in annual mean\nPM2.5 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\nthe government for air quality control are -9.3±1.8 µg m−3 a−1 (±95 % confidence interval) for Beijing–Tianjin–Hebei,\n-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\nobservations of sulfur dioxide (SO2) and carbon monoxide (CO) show that\nthe declines in PM2.5 are qualitatively consistent with drastic\ncontrols of emissions from coal combustion. However, there is also a large\nmeteorologically driven interannual variability in PM2.5 that\ncomplicates trend attribution. We used a stepwise multiple linear regression\n(MLR) model to quantify this meteorological contribution to the PM2.5 trends across China. The MLR model correlates the 10 d PM2.5\nanomalies to wind speed, precipitation, relative humidity, temperature, and\n850 hPa meridional wind velocity (V850). The meteorology-corrected\nPM2.5 trends after removal of the MLR meteorological contribution can\nbe viewed as being driven by trends in anthropogenic emissions. The mean\nPM2.5 decrease across China is −4.6 µg m−3 a−1 in the\nmeteorology-corrected data, 12 % weaker than in the original data, meaning\nthat 12 % of the PM2.5 decrease in the original data is\nattributable to meteorology. The trends in the meteorology-corrected data\nfor the five megacity clusters are -8.0±1.1 µg m−3 a−1 for Beijing–Tianjin–Hebei (14 % weaker than in the original\ndata), -6.3±0.9 µg m−3 a−1 for the Yangtze River Delta\n(3 % stronger), -2.2±0.5 µg m−3 a−1 for the Pearl River\nDelta (19 % weaker), -4.9±0.9 µg m−3 a−1 for\nthe 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\nflattening PM2.5 in the Pearl River Delta and increases in the Fenwei\nPlain can be attributed to meteorology rather than to relaxation of emission\ncontrols.\n

/pdf/fine-particulate-matter-pm-2-5-trends-in-china-2013-2018-4nxiozdatx.pdf

Fine particulate matter (PM 2.5 ) trends in China, 2013–2018: separating contributions from anthropogenic emissions and meteorology

Formation, features and controlling strategies of severe haze-fog pollutions in China

Satellite-based mapping of daily high-resolution ground PM 2.5 in China via space-time regression modeling

. Frequent low visibility, haze and fog events were found in the North China Plain (NCP). Data throughout the NCP during the past 30 years were examined to determine the horizontal distribution and decadal trends of low visibility, haze and fog events. The impact of meteorological factors such as wind and relative humidity (RH) on those events was investigated. Results reveal distinct distributions of haze and fog days, due to their different formation mechanisms. Low visibility, haze and fog days all display increasing trends of before 1995, a steady stage during the period 1995–2003 and a drastically drop thereafter. All three events occurred most frequently during the heating season. Benefiting from emission control measures, haze and fog both show decreasing trends in winter during the past 3 decades, while summertime haze displays continuous increasing trends. The distribution of wind speed and wind direction as well as the topography within the NCP has determinative impacts on the distribution of haze and fog. Weakened south-easterly winds in the southern part of the NCP have resulted in high pollutant concentrations and frequent haze events along the foot of the Taihang Mountains. The orographically generated boundary layer wind convergence line in the central area of the southern NCP is responsible for the frequent fog events in this region. Wind speed has been decreasing throughout the entire southern NCP, resulting in more stable atmospheric conditions and weaker dispersion abilities, calling for harder efforts to control emissions to prevent haze events. Haze events are strongly influenced by the ambient RH. RH values associated with haze days are evidently increasing, suggesting that an increasing fraction of haze events are caused by the hygroscopic growth of aerosols, rather than simply by high aerosol loadings.

/pdf/the-distribution-and-trends-of-fog-and-haze-in-the-north-19j1xvox2f.pdf

G. Q. Fu

Papers

The distribution and trends of fog and haze in the North China Plain over the past 30 years