Abstract
ABSTRACT Daily PM2.5 samples were collected at a rural background station (JinYun) located in Chongqing across four consecutive seasons from October 2014 to July 2015. The major water-soluble inorganic ions (WSIIs), organic carbon (OC) and elemental carbon (EC) were analyzed, and their chemical characteristics, transport pathways and potential source regions were investigated. The average annual PM2.5 concentration was 56.2 ± 31.0 µg m–3, of which secondary inorganic aerosol (SNA) and carbonaceous aerosols composed 41.0% and 29.4%, respectively. Higher concentrations of and contributions from SO42–, which were likely caused by the secondary transformation of SO2 into SO42–, were observed in summer than in autumn and spring. Additionally, transportation from the urban area of Chongqing (Yubei) played an important role in elevating the SO42– during this season. Although the accumulation of PM2.5 during pollution episodes in winter was also due to aqueous-phase reactions, based on the entire year, NO3– formation may have been primarily driven by homogeneous gas-phase reactions. Furthermore, the aerosol environment was ammonium-rich, and NH4+ formation promoted the production of NO3– at lower temperatures. The carbonaceous component, which consisted of 81.0–84.6% OC, exhibited higher concentrations in winter than in the other seasons; 50.0–77.2% of the total OC, in turn, was contributed by primary organic carbon (POC). Potential source contribution function (PSCF) analysis suggests that the site was mainly affected by regional pollution originating in the southwestern and northern areas of Chongqing.
Highlights
Atmospheric fine particles (PM2.5, particulate matter with an aerodynamic diameter ≤ 2.5 μm) negatively impact human health, air quality, and atmospheric visibility (Anderson et al, 2012; Cao et al, 2012; Deng et al, 2014; Deng et al, 2016a; Fu et al, 2016)
Different from the typical seasonal pattern observed in the urban areas of China, i.e., lowest in summer (He et al, 2001; Wang et al, 2015; Wang et al, 2018b; Qiao et al, 2019), the seasonal average concentration of PM2.5 was higher in summer (52.1 ± 9.4 μg m–3) than in spring (43.9 ± 18.0 μg m–3) and autumn (39.0 ± 17.5 μg m–3) at JinYun mountain (JY), though it was not significant (p > 0.05) (Fig. S2, Table 1)
The concentration of SO42– and SO2 in JY showed higher correlation coefficients with that in YB in summer (R2 = 0.883, 0.749), and the slopes of the linear regression were closer to 1 (0.96, 0.91) in summer (Figs. 2(c) and 2(d)). These results indicated that the regional transport of SO42– and SO2 from urban area (YB) could be an important source of SO42– aerosols at JY site in summer
Summary
Atmospheric fine particles (PM2.5, particulate matter with an aerodynamic diameter ≤ 2.5 μm) negatively impact human health, air quality, and atmospheric visibility (Anderson et al, 2012; Cao et al, 2012; Deng et al, 2014; Deng et al, 2016a; Fu et al, 2016). Annual average PM2.5 concentration is declining recently due to the implementation of several measures, PM2.5 pollution was still serious in some megacities such as Beijing-Tianjin-Hebei, Yangtze River Delta, Pearl River Delta, and Sichuan Basin (Tao et al, 2017). Chongqing was one of the most important industrial cities in Sichuan Basin and had severe aerosol pollution (Tian et al, 2017a; Wang et al, 2018b). The annual mean concentration of PM2.5 was 70.9 ± 41.4 μg m–3 during 2014–2015 at Chongqing, which was about 2 times the secondary grade limit specified in the Chinese National Ambient Air Quality Standards (NAAQS) (Wang et al, 2018b).
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