In:
Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 18, No. 6 ( 2018-03-20), p. 3919-3935
Abstract:
Abstract. A rapid development of a severe air pollution event in Beijing, China, at the end of November 2015 was investigated with
unprecedented observations collected during the field campaign of the Study of Urban Rainfall and Fog/Haze
(SURF-15). Different from previous statistical analyses of air pollution events and their correlations with meteorological
environmental conditions in the area, the role of turbulent mixing in the pollutant transfer was investigated in
detail. The analyses indicate that the major pollution source associated with high particulate matter of diameter
2.5 µm (PM2.5) was from south of Beijing. Before the day of the dramatic PM2.5 increase, the
nighttime downslope flow from the mountains to the west and north of Beijing reduced the surface PM2.5
concentration northwest of Beijing. The nighttime surface stable boundary layer (SBL) not only kept the relatively
less-polluted air near the surface, it also shielded the rough surface from the pollutant transfer by southwesterly winds above
the SBL, leading to the fast transport of pollutants over the Beijing area at night. As the daytime convective turbulent
mixing developed in the morning, turbulent mixing transported the elevated polluted air downward even though the weak
surface wind was from northeast, leading to the dramatic increase of the surface PM2.5 concentration in the
urban area. As a result of both turbulent mixing and advection processes with possible aerosol growth from secondary
aerosol formation under the low-wind and high-humidity conditions, the PM2.5 concentration reached over
700 µg m−3 in the Beijing area by the end of the day. Contributions of the two transporting processes to
the PM2.5 oscillations prior to this dramatic event were also analyzed. The study demonstrates the important
role of large-eddy convective turbulent mixing in vertical transfer of pollutants and the role of the SBL in not only
decoupling vertical transport of trace gases and aerosols but also in accelerating horizontal transfer of pollutants
above.
Type of Medium:
Online Resource
ISSN:
1680-7324
DOI:
10.5194/acp-18-3919-2018
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2018
detail.hit.zdb_id:
2092549-9
detail.hit.zdb_id:
2069847-1
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