18 October 2019

Long-Distance Soot Clogs the Winter Air in China

Arctic and midlatitude black carbon particles intensify haze over the North China Plain by weakening the East Asian winter monsoon.

Science

In recent years, China has experienced severe and persistent winter haze linked to air stagnation and burning wood or coal. A study led by scientists at the U.S. Department of Energy’s Pacific Northwest National Laboratory revealed the influence of Arctic and midlatitude black carbon (BC)—or soot particles—on meteorology and haze in the North China Plain. Researchers found that both Arctic and midlatitude BC can thicken haze over the heavily populated North China Plain by weakening the East Asian winter monsoon. As BC travels through the atmosphere over the ocean, it changes cloud structure and the contrast between land and sea temperatures. This leads to decreased wind speeds, weaker rainfall, and stagnant air.

Impact

Previous studies showed that fine aerosol particles, such as dust, can travel long distances through the atmosphere and influence global climate and air quality. The findings from this study suggest that reducing Arctic and midlatitude BC emissions could have significant indirect benefits for air quality and human health in the North China Plain.

Summary

Rapid population and industrial growth in the North China Plain have led to poor air quality in the region. Haze events in the North China Plain can be particularly extreme during the winter, when fuel combustion emissions from heating increase and meteorological conditions stagnate. This leads to an accumulation of particles in the atmosphere. Recent studies reported that BC could intensify pollution in China by suppressing the lower atmosphere (i.e., weakening both vertical air mixing and dispersion of particle plumes). Researchers examined the response of meteorological variables associated with the East Asian winter monsoon to BC emissions from Arctic and midlatitude sources. For their simulations, they used the Community Earth System Model, a fully coupled global aerosol-climate model. They found that, in addition to their effect on local atmospheric mixing, increased BC emissions can intensify particle pollution in the North China Plain by weakening the East Asian winter monsoon through ocean, sea-ice, and cloud responses. 

Contact
Hailong Wang
Pacific Northwest National Laboratory
Publications
Lou, S, Y Yang, H Wang, S Smith, Y Qian, and H Wang.  2019.  "Black Carbon Amplifies Haze Over the North China Plain by Weakening the East Asian Winter Monsoon."  Geophysical Research Letters 46(1): 452-460.  https://doi.org/10.1029/2018gl080941.