Recent Intensification of Winter Haze in China Linked to Foreign Emissions and Meteorology
Pollution in China—particularly in the heavily populated North China Plain—has shown steep increases since the beginning of the 21st century. A study by scientists at the U.S. Department of Energy’s Pacific Northwest National Laboratory revealed the influence of meteorology and domestic and foreign emissions on aerosol trends in China from 1980–2014. Researchers found that decreased reductions in foreign emissions, together with weakening of winds, explained about 25 percent of the increased aerosol trend in China this century compared to 1980–2000.
Previous studies showed that fine aerosol particles can reach distant and remote areas via long-range transport, resulting in global effects on climate and air quality. However, contributions to aerosol in the North China Plain from distant foreign sources have stabilized since the beginning of the 21st century, and limited further reductions are foreseen. Therefore, reducing local emissions is the most certain way to improve future air quality in the North China Plain.
Rapid population and industrial growth in the North China Plain has led to poor air quality in the region characterized by high concentrations of particulate matter less than 2.5 microns in diameter (PM2.5). During the winter, haze events in the North China Plain and other parts of the country can be particularly extreme, as meteorological conditions stagnate and lead to an accumulation of aerosol particles in the atmosphere.
Researchers quantified the recent intensification of winter haze in China for the time period of 1980−2014, using an aerosol source tagging capability in the Community Atmosphere Model (version 5), a global aerosol-climate model. In particular, they looked at variations of wintertime PM2.5 concentrations on decadal timescales for the North China Plain. They found that, over the last two decades of the 20th century, decreased foreign emissions offset by 13 percent the effect of China’s increasing domestic emissions on PM2.5 concentrations. As foreign emissions stabilized after 2000, their counteracting effect almost disappeared, revealing the impact of China’s increasing domestic emissions. A decrease in foreign emission reductions along with weakening winds explained 25 percent of the increased PM2.5 trend during 2000–2014 as compared to 1980–2000. These findings highlight the contribution of foreign emissions to historical changes in haze occurrence in the North China Plain that need to be taken into account in air quality studies.