Abstract
Abstract. Air pollution by particulate matter in China affects human health, the ecosystem and the climate. However, the chemical composition of particulate aerosol, especially of the organic fraction, is still not well understood. In this study, particulate aerosol samples with a diameter of ≤2.5 µm (PM2.5) were collected in January 2014 in three cities located in northeast, east and southeast China, namely Changchun, Shanghai and Guangzhou. Organic aerosol (OA) in the PM2.5 samples was analyzed by an ultrahigh-performance liquid chromatograph (UHPLC) coupled to a high-resolution Orbitrap mass spectrometer in both negative mode (ESI-) and positive mode electrospray ionization (ESI+). After non-target screening including the assignment of molecular formulas, the compounds were classified into five groups based on their elemental composition, i.e., CHO, CHON, CHN, CHOS and CHONS. The CHO, CHON and CHN groups present the dominant signal abundances of 81 %–99.7 % in the mass spectra and the majority of these compounds were assigned to mono- and polyaromatics, suggesting that anthropogenic emissions are a major source of urban OA in all three cities. However, the chemical characteristics of these compounds varied between the different cities. The degree of aromaticity and the number of polyaromatic compounds were substantially higher in samples from Changchun, which could be attributed to the large emissions from residential heating (i.e., coal combustion) during wintertime in northeast China. Moreover, the ESI- analysis showed higher H/C and O/C ratios for organic compounds in Shanghai and Guangzhou compared to samples from Changchun, indicating that OA undergoes more intense photochemical oxidation processes in lower-latitude regions of China and/or is affected to a larger degree by biogenic sources. The majority of sulfur-containing compounds (CHOS and CHONS) in all cities were assigned to aliphatic compounds with low degrees of unsaturation and aromaticity. Here again, samples from Shanghai and Guangzhou show a greater chemical similarity but differ largely from those from Changchun. It should be noted that the conclusions drawn in this study are mainly based on comparison of molecular formulas weighted by peak abundance and thus are associated with inherent uncertainties due to different ionization efficiencies for different organic species.
Highlights
In the last decades, China has experienced rapid industrialization and urbanization accompanied by severe and persistent particulate air pollution (Huang et al, 2014; Sun et al, 2014; Ding et al, 2016; Song et al, 2018; Shi et al, 2019; Xu et al, 2019)
The largest number of organic compounds was observed in Changchun samples in both ESI- and ESI+, indicating that Organic aerosol (OA) collected during the winter season in northeast China was more complex compared to urban OA in east and southeast China
120 common formulas were detected in ESI- and 129 common formulas in ESI+ for all sample locations, accounting for 57 %–71 % and 30 %–75 % in terms of peak abundance, respectively
Summary
China has experienced rapid industrialization and urbanization accompanied by severe and persistent particulate air pollution (Huang et al, 2014; Sun et al, 2014; Ding et al, 2016; Song et al, 2018; Shi et al, 2019; Xu et al, 2019). These particulate air pollution extremes can influence the regional air quality and human health in China, and lead to a global environmental problem due to long-distance transport of pollutants. The insufficient knowledge of chemical composition of OA hinders a better understanding of the sources, formation and atmospheric processes of air pollution in China
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