Observational analyses of dramatic developments of a severe air pollution event in the Beijing area

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.

Diminishing clear winter skies in Beijing towards a possible future

“…We then design a CDI, obtained by a combination of the individual conditions, to facilitate comparative analyses of such extreme events between different periods of the last century and between the simulated historical and future climate. For the period The haze intensity (pollution level) is also important, which largely depends on local emissions, regional pollutant transport, generation mechanisms for secondary pollution as well as meteorological conditions (Huang et al 2014, Zhang et al 2014, Li et al 2018a. For pollution in Beijing, vehicles, coal combustion and cross-regional transport are equally important sources of PM 2.5 (He et al 2013).…”

“…Air pollution is a particularly acute problem, as it affects the daily life of more than two-thirds of China's entire population (Liu andDiamond 2005, Zhang 2017). Winter haze has been choking citizens across major cities, such as the capital (Beijing), which has culminated during haze episodes in the winters of 2013, 2015 and 2016 (Zhang et al 2014, Zhu et al 2016, Yin and Wang 2017, Li et al 2018a. Severe haze leads to a sharp decrease in visibility, causing traffic hazards and disruptions, and, hence, affecting economic activities (Huang et al 2014, Chen and Wang 2015, Li et al 2016.…”

Multiple technical observations of the atmospheric boundary layer structure of a red-alert haze episode in Beijing

“…Regarding air pollution, many observational experiments have been conducted internationally, especially with reference to air pollution in the ABL over urban areas (i.e., the urban boundary layer). Examples of such projects include European Cooperation in the Field of Scientific and Technical Research, abbreviated as COST715 (Fisher et al, 2001); URBAN 2000, a major urban tracer and meteorological field campaign conducted in Salt Lake City, UT, in October 2000 (Allwine et al, 2002); Joint Urban 2003, a field experiment conducted in October 2003 in Oklahoma City, OK (Wang et al, 2007); MIRAGE 2006, Megacity Impacts on Regional and Global Environments (Lance et al, 2012); and SURF, the Study of Urban impacts on Rainfall and Fog/haze (Liang et al, 2018).…”

Aerosol vertical mass flux measurements during heavy aerosol pollution episodes at a rural site and an urban site in the Beijing area of the North China Plain

“…Y. Zhang et al, 2009;Huang et al, 2014). Modelling studies have also been performed to examine the regional transport of pollutants (Wang et al, 2014) and to study the important role of large-eddy convective turbulent mixing in the vertical transfer of pollutants from a field campaign in Beijing (Li et al, 2018). However, few studies on the turbulence contribution of the aerosol turbulent flux in the surface layer have been conducted.…”

“…A numerical model has also been used to estimate average fleet emission factors in typical urban conditions (Ketzel et al, 2003;Krecl et al, 2018). The uncertainties in the emissions of primary aerosols for inventories are high due to the highly uncertain contributions from the residential sector (Li et al, 2017), and the error in aerosol fluxes based on the use of emission inventories is huge (Liu et al, 2017;Zheng et al, 2017). Emission inventories constructed using the EF method provide only the total emission amount of atmospheric pollutants within a region.…”