Characteristics of PM 2.5 mass concentrations and chemical species in urban and background areas of China: emerging results from the CARE-China network

Liu, Zirui; Gao, Wenkang; Yu, Yangchun; Hu, Bo; Xin, Jinyuan; Sun, Yang; Wang, Lili; Wang, Gehui; Bi, Xinhui; Zhang, Guohua; Xu, Honghui; Cong, Zhiyuan; He, Jun; Xu, Jingsha; Wang, Yuesi

page8850The “Campaign on Atmospheric Aerosol Research” network of China (CARE-China) is a long-term project for the study of the spatio-temporal distributions of physical aerosol characteristics as well as the chemical components and optical properties of aerosols over China. This study presents the first long-term data sets from this project, including 3 years of observations of online PMinline-formula2.5 mass concentrations (2012–2014) and 1 year of observations of PMinline-formula2.5 compositions (2012–2013) from the CARE-China network. The average PMinline-formula2.5 concentration at 20 urban sites is 73.2 inline-formulaµg minline-formula−3 (16.8–126.9 inline-formulaµg minline-formula−3), which was 3 times higher than the average value from the 12 background sites (11.2–46.5 inline-formulaµg minline-formula−3). The PMinline-formula2.5 concentrations are generally higher in east-central China than in the other parts of the country due to their relatively large particulate matter (PM) emissions and the unfavourable meteorological conditions for pollution dispersion. A distinct seasonal variability in PMinline-formula2.5 is observed, with highs in the winter and lows during the summer at urban sites. Inconsistent seasonal trends were observed at the background sites. Bimodal and unimodal diurnal variation patterns were identified at both urban and background sites. The chemical compositions of PMinline-formula2.5 were analysed at six paired urban and background sites located within the most polluted urban agglomerations – North China Plain (NCP), Yangtze River delta (YRD), Pearl River delta (PRD), North-east China region (NECR), South-west China region (SWCR) – and the cleanest region of China – the Tibetan Autonomous Region (TAR). The major PMinline-formula2.5 constituents across all the urban sites are organic matter (OM, 26.0 %), inline-formula M16inlinescrollmathml chem normal SO normal 4 normal 2 - 29pt17ptsvg-formulamathimg996ea863b6d2357cf65489687f93a05f acp-18-8849-2018-ie00001.svg29pt17ptacp-18-8849-2018-ie00001.png (17.7 %), mineral dust (11.8 %), inline-formula M17inlinescrollmathml chem normal NO normal 3 - 25pt16ptsvg-formulamathimg822fcc3376206f5298bc14405cca7022 acp-18-8849-2018-ie00002.svg25pt16ptacp-18-8849-2018-ie00002.png (9.8 %), inline-formula M18inlinescrollmathml chem normal NH normal 4 + 24pt15ptsvg-formulamathimg7b888eb222795ca6a6dd2ceb535b59a0 acp-18-8849-2018-ie00003.svg24pt15ptacp-18-8849-2018-ie00003.png (6.6 %), elemental carbon (EC) (6.0 %), inline-formulaCl (1.2 %) at 45 % RH and unaccounted matter (20.7 %). Similar chemical compositions of PMinline-formula2.5 were observed at background sites but were associated with higher fractions of OM (33.2 %) and lower fractions of inline-formula M21inlinescrollmathml chem normal NO normal 3 - 25pt16ptsvg-formulamathimg8a28d0a06c83cc478fcb3953dfc5e6ea acp-18-8849-2018-ie00004.svg25pt16ptacp-18-8849-2018-ie00004.png (8.6 %) and EC (4.1 %). Significant variations of the chemical species were observed among the sites. At the urban sites, the OM ranged from 12.6 inline-formulaµg minline-formula−3 (Lhasa) to 23.3 inline-formulaµg minline-formula−3 (Shenyang), the inline-formula M26inlinescrollmathml chem normal SO normal 4 normal 2 - 29pt17ptsvg-formulamathimge74435277bc316ae776b5cb3f2b0ff2d acp-18-8849-2018-ie00005.svg29pt17ptacp-18-8849-2018-ie00005.png ranged from 0.8 inline-formulaµg minline-formula−3 (Lhasa) to 19.7 inline-formulaµg minline-formula−3 (Chongqing), the inline-formula M31inlinescrollmathml chem normal NO normal 3 - 25pt16ptsvg-formulamathimge7b5cbf4b302fb927b8bd090b8fd0240 acp-18-8849-2018-ie00006.svg25pt16ptacp-18-8849-2018-ie00006.png ranged from 0.5 inline-formulaµg minline-formula−3 (Lhasa) to 11.9 inline-formulaµg minline-formula−3 (Shanghai) and the EC ranged from 1.4 inline-formulaµg minline-formula−3 (Lhasa) to 7.1 inline-formulaµg minline-formula−3 (Guangzhou). The PMinline-formula2.5 chemical species at the background sites exhibited larger spatial heterogeneities than those at urban sites, suggesting different contributions from regional anthropogenic or natural emissions and from long-range transport to background areas. Notable seasonal variations of PMinline-formula2.5-polluted days were observed, especially for the megacities in east-central China, resulting in frequent heavy pollution episodes occurring during the winter. The evolution of the PMinline-formula2.5 chemical compositions on polluted days was consistent for the urban and nearby background sites, where the sum of sulfate, nitrate and ammonia typically constituted much higher fractions (31–57 %) of PMinline-formula2.5 mass, suggesting fine-particle pollution in the most polluted areas of China assumes a regional tendency, and the importance of addressing the emission reduction of secondary aerosol precursors including inline-formulaSO2 and inline-formulaNOx. Furthermore, distinct differences in the evolution of inline-formula M46inlinescrollmathml chem [ normal NO normal 3 - ] / [ normal SO normal 4 normal 2 - ] 69pt17ptsvg-formulamathimg156c2cd5cb6077dc46029f0817afbb6b acp-18-8849-2018-ie00007.svg69pt17ptacp-18-8849-2018-ie00007.png ratio and inline-formulaOC∕EC ratio on polluted days imply that mobile sources and stationary (coal combustion) sources are likely more important in Guangzhou and Shenyang, respectively, whereas in Beijing it is mobile emission and residential sources. As for Chongqing, the higher oxidation capacity than the other three cities suggested it should pay more attention to the emission reduction of secondary aerosol precursors. This analysis reveals the spatial and seasonal variabilities of the urban and background aerosol concentrations on a national scale and provides insights into their sources, processes and lifetimes.

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Liu, Zirui / Gao, Wenkang / Yu, Yangchun / et al: Characteristics of PM2.5 mass concentrations and chemical species in urban and background areas of China: emerging results from the CARE-China network. 2018. Copernicus Publications.

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