The interaction between urbanization and aerosols during a typical winter haze event in Beijing

Miao Yu,Qingchun Li,Yang Yang,Yizhou Zhang,Shiguang Miao,Yonghong Wang,Yuesi Wang,Guiqian Tang

doi:10.5194/acp-20-9855-2020

Abstract

Abstract. Aerosols cause cooling at the surface by reducing shortwave radiation, while urbanization causes warming by altering the surface albedo and releasing anthropogenic heat. The combined effect of the two phenomena needs to be studied in depth. The effects of urbanization and aerosols were investigated during a typical winter haze event. The event, which occurred in Beijing from 15 to 22 December 2016, was studied via the Rapid-Refresh Multiscale Analysis and Prediction System – Short Term (RMAPS-ST) model. The mechanisms of the impacts of aerosols and urbanization were analyzed and quantified. Aerosols reduced urban-related warming during the daytime by 20 % (from 30 % to 50 %) as concentrations of fine particulate matter (PM2.5) increased from 200 to 400 µg m−3. Conversely, aerosols also enhanced urban-related warming at dawn, and the increment was approximately 28 %, which contributed to haze formation. Urbanization reduced the aerosol-related cooling effect by approximately 54 % during the haze event, and the strength of the impact changed little with increasing aerosol content. The impact of aerosols on urban-related warming was more significant than the impact of urbanization on aerosol-related cooling. Aerosols decreased the urban impact on the mixing-layer height by 148 % and on the sensible heat flux by 156 %. Furthermore, aerosols decreased the latent heat flux; however, this reduction decreased by 48.8 % due to urbanization. The impact of urbanization on the transport of pollutants was more important than that of aerosols. The interaction between urbanization and aerosols may enhance the accumulation of pollution and weigh against diffusion.

Highlights

In recent years, heavy-haze pollution events have increasingly occurred in densely populated urban areas, such as the Beijing–Tianjin–Hebei region (BTH region) and Yangtze River Delta region of China (Zhang et al, 2019)
Urbanization reduced the aerosol-related cooling effect by approximately 54 % during the haze event, and the strength of the impact changed little with increasing aerosol content
There is no urban impact on downward shortwave radiation or an impact of aerosols on shortwave radiation

Summary

Introduction

Heavy-haze pollution events have increasingly occurred in densely populated urban areas, such as the Beijing–Tianjin–Hebei region (BTH region) and Yangtze River Delta region of China (Zhang et al, 2019). These events have caused increasingly severe adverse effects on transportation, the ecological environment, and human health (Zhao et al, 2012; Wu et al, 2010; Liu et al, 2012). A statistical analysis of the variation in haze days in Beijing over the past 10 years showed that the number of haze days has significantly increased (Chen and Wang, 2015; Zhai et al, 2019). Meteorological conditions, terrain, and high-density human activities in urban areas are all important conditions for the evolution of heavy haze (Huang et al, 2008a; Zhu et al, 2018), meteorological conditions are critical for the evolution of heavy-haze pollution weather under the background of constant emissions (Wang et al, 2020; Pei et al, 2020)

Objectives

Methods

Results

Discussion

Conclusion