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Variations of Chemical Composition and Source Apportionment of PM2.5 during Winter Haze Episodes in Beijing

Category: Urban Air Quality

Volume: 17 | Issue: 11 | Pages: 2791-2803
DOI: 10.4209/aaqr.2017.10.0366
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Qingxia Ma1,2, Yunfei Wu 1, Jun Tao3, Yunjie Xia1, Xinyu Liu1, Daizhou Zhang4, Zhiwei Han1, Xiaoling Zhang5, Renjian Zhang 1

  • 1 CAS Key Laboratory of Regional Climate–Environment for Temperate East Asia, Institute of Atmosphere Physics, Chinese Academy of Sciences, Beijing 100029, China
  • 2 College of Earth Sciences, University of Chinese Academy of Sciences, Beijing 100864, China
  • 3 South China Institute of Environmental Sciences, Ministry of Environmental Protection, Guangdong 510655, China
  • 4 Faculty of Environmental and Symbiotic Sciences, Prefectural University of Kumamoto, Kumamoto 862-8502, Japan
  • 5 School of Atmospheric Sciences/Plateau Atmosphere and Environment Key Laboratory of Sichuan Province, Chengdu University of Information Technology, Sichuan 610225, China

Highlights

The contributions of SIA to PM2.5 increased with pollution level increasing.
The contributions of OC and EC to PM2.5 decreased as the pollution level increased.
Industry emission dominated the PM2.5 in the clean period.
SIA was the largest origin of PM2.5 at the heavy and severe pollution levels.


Abstract

PM2.5 samples were collected in Beijing between February 24 and March 12 of 2014, and analyzed to examine chemical compositions and origins of the PM2.5 at pollution levels of clean (PM2.5 < 75 µg m–3), light-medium (75–150 µg m–3), heavy (150–250 µg m–3) and severe (> 250 µg m–3). The mean PM2.5 concentration was 137.7 ± 124.8 µg m–3 during the observation period, accounting for 66% of PM10. As all aerosol species concentrations increased with the pollution level, the contributions of secondary inorganic aerosols (SIA) to PM2.5 continuously increased while the contributions of OC and EC decreased, indicating a substantial contribution from secondary formation to the elevation of PM2.5 pollution. The acidity of PM2.5, the ratio of anion microequivalent concentration to cation, increased from 0.96 to 1.08 as pollution levels increased. Using a PMF model, secondary inorganic aerosols, industrial emissions, soil dust, traffic emissions, and coal combustion and biomass burning were identified as contributors to the PM2.5, and on average accounted 46%, 20%, 10%, 6% and 18% of the PM2.5, respectively, in the observation period. Industrial emissions were the dominant PM2.5 source during the clean period (60%). Except for traffic emission, sources of PM2.5 at the light-medium level were consistent, accounting for 17%–29%. Secondary inorganic aerosols were the largest origin of PM2.5 at heavy and severe pollution levels, accounting for 40% and 78%, respectively. In addition, the 48 h transport distances of air masses decreased from 2000 km (clean) to 300 km (severe level) and the proportion of air masses from south pollution areas in the total air masses at each pollution level increased from 0% to 97%, indicating that the stability of near surface air and the northerly transport of pollutants from the south at local and regional scales played a the key role in the PM2.5 elevation.

Keywords

Pollution levels Chemical characteristics Sources Air trajectories China


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