Mixing layer transport flux of particulate matter in Beijing, China Guiqian Tang, Xiaowan Zhu, Yusi Liu, Libo Zhou, Bo Hu, Yuesi Wang Institute of Atmospheric Physics, Chinese Academy of Sciences April, 2019

Motivation PM2.5 WHO 35μg/m3 Raising the emission standards of motor vehicles and fuel standards for vehicles, changing coal to natural gas, coal to electricity pollutants tend to accumulate in front of the mountains due to the influence of southerly winds and mountain obstruction. Great pressure to ensure continuous decline of PM. Regional pollution → Joint prevention and control (Shen et al., 2019, STE; Cheng et al., 2018, ACPD)

How to implement joint emission control at the lowest economic cost? Main targets Red alert of air pollution in China → close nearly all the industries How to implement joint emission control at the lowest economic cost? What are the responses of particulate matter to boundary layer meteorology When and where should be controlled during heavy pollution episodes ? Joint prevention and control have been put forward for a long time, but it is still unknow when and where to control. ?

Methods Horizontal dilution capacity Vertical dilution capacity Vertical aerosols profile Mixing layer height To analyze dilution capability, MLH was observed by a single-lens ceilometer, and the wind profile in the mixing layer was simultaneously observed by doppler wind radar. Vertical wind profile Doppler wind radar Ceilometer CL51

Methods Uniform vertical backscatter coefficient → using ground PM concentration to represent the average concentration in ML Flux = VC × C PM2.5

The connection between boundary meteorology and air quality Periodicity of PM, MLH and RH Sawtooth PM cycle Sawtooth MLH and RH The connection between boundary meteorology and air quality (Tang et al., ACP, 2016; Zhu, Tang*, JGR, 2016)

Responses of PM to boundary layer meteorology in winter PM2.5 concentration is highly sensitive to boundary layer meteorology in winter. VC had a better correlation with the PM2.5 concentration than MLH and WSML, indicating that VC can better characterize pollution dissipation. Weak atmospheric dilution capability is a crucial factor leading to serious air pollution in Beijing. (Liu, Tang* et al., 2019, ACPD)

Responses of PM to boundary layer meteorology in summer Weak positive correlation in summer Secondary particles because of high ozone ? (Liu, Tang* et al., 2019, ACPD)

Inconsistent diurnal cycles of ozone and PM Responses of PM to boundary layer meteorology in summer Inconsistent diurnal cycles of ozone and PM Secondary formation is not the main reason.

Mountainous plain winds in Beijing Strong southwest winds in the afternoon, but northly winds before the next day’s afternoon. (Tang et al., 2016, ACP; Liu, Tang* et al., 2019, ACPD)

Impact of mountainous plain winds on particulate matter June as an example We find that except in winter, the northeast prevails in the morning and the southwest prevails in the afternoon. Combined with the topographic characteristics of Beijing, this is a typical mountain and plain wind circulation. Take June as an example, the PM concentration appears high before noon, indicating … The circulation of mountain plain winds leads to high PM2.5 before noon. (Liu, Tang* et al., 2019, ACPD)

Transport flux under different degrees of air pollution We find that except in winter, the northeast prevails in the morning and the southwest prevails in the afternoon. Combined with the topographic characteristics of Beijing, this is a typical mountain and plain wind circulation. Take June as an example, the PM concentration appears high before noon, indicating … Regional transport plays an important role in the transition period of pollution. Local emissions are the main controlling factor during the period of heavy pollution . (Tang et al,, 2015, ACP; Liu, Tang* et al., 2019, ACPD)

Summary PM2.5 concentration is highly sensitive to boundary layer meteorology. The mountainous plain circulation influence the air quality in summer. In the transition period of air pollution, the focus should be on controlling the emissions in the south of Beijing.

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