Analysis of the causes of heavy aerosol pollution in Beijing, China: A case study with the WRF-Chem model--颗粒学报PARTICUOLOGY

He, H., Tie, X., Zhang, Q., Liu, X., Gao, Q., Li, X., & Gao, Y. (2015). Analysis of the causes of heavy aerosol pollution in Beijing, China: A case study with the WRF-Chem model. Particuology, 20, 32–40. https://doi.org/10.1016/j.partic.2014.06.004

Analysis of the causes of heavy aerosol pollution in Beijing, China: A case study with the WRF-Chem model

Hui He ^a, Xuexi Tie ^{b c *}, Qiang Zhang ^a, Xiange Liu ^a, Qian Gao ^a, Xia Li ^a, Yang Gao ^a

a Beijing Weather Modification Office, Beijing 100089, China
b Key Laboratory of Aerosol Science and Technology, SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710049, China
c National Center for Atmospheric Research, Boulder, CO, USA

10.1016/j.partic.2014.06.004

Volume 20, June 2015, Pages 32-40

Received 16 February 2014, Revised 9 June 2014, Accepted 11 June 2014, Available online 27 September 2014.

E-mail: xxtie@ucar.edu; tiexx@ieecas.cn

Highlights

• An aerosol pollution episode was analyzed to study the causes and variability of the heavy haze.

• Intensive in situ measurements were used in this study.

• WRF-Chem model was used to study contribution of local and regional emissions to the heavy haze.

• The weak wind and low PBL height played important roles for the formation of the heavy haze.

• During this episode, the local emission was the major cause for the formation of the heavy haze.

Abstract

The causes and variability of a heavy haze episode in the Beijing region was analyzed. During the episode, the PM_2.5 concentration reached a peak value of 450 μg/kg on January 18, 2013 and rapidly decreased to 100 μg/kg on January 19, 2013, characterizing a large variability in a very short period. This strong variability provides a good opportunity to study the causes of the haze formation. The in situ measurements (including surface meteorological data and vertical structures of the winds, temperature, humidity, and planetary boundary layer (PBL)) together with a chemical/dynamical regional model (WRF-Chem) were used for the analysis. In order to understand the rapid variability of the PM_2.5 concentration in the episode, the correlation between the measured meteorological data (including wind speed, PBL height, relative humidity, etc.) and the measured particle concentration (PM_2.5 concentration) was studied. In addition, two sensitive model experiments were performed to study the effect of individual contribution from local emissions and regional surrounding emissions to the heavy haze formation. The results suggest that there were two major meteorological factors in controlling the variability of the PM_2.5 concentration, namely, surface wind speed and PBL height. During high wind periods, the horizontal transport of aerosol particles played an important role, and the heavy haze was formed when the wind speeds were very weak (less than 1 m/s). Under weak wind conditions, the horizontal transport of aerosol particles was also weak, and the vertical mixing of aerosol particles played an important role. As a result, the PBL height was a major factor in controlling the variability of the PM_2.5 concentration. Under the shallow PBL height, aerosol particles were strongly confined near the surface, producing a high surface PM_2.5 concentration. The sensitivity model study suggests that the local emissions (emissions from the Beijing region only) were the major cause for the heavy haze events. With only local emissions, the calculated peak value of the PM_2.5 concentration was 350 μg/kg, which accounted for 78% of the measured peak value (450 μg/kg). In contrast, without the local emissions, the calculated peak value of the PM_2.5 concentration was only 100 μg/kg, which accounted for 22% of the measured peak value.

Graphical abstract

Keywords

PM_2.5 in Beijing; Causes of heavy haze; Planetary boundary layer (PBL); WRF-Chem model

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