Abstract
To track the particulate pollution in Sichuan Basin, sample filters were collected in three urban sites. Characteristics of water-soluble inorganic ions (WSIIs) were explored and their sources were analyzed by principal component analysis (PCA). During 2012–2013, the PM2.5 concentrations were 86.7 ± 49.7 μg m−3 in Chengdu (CD), 78.6 ± 36.8 μg m−3 in Neijiang (NJ), and 71.7 ± 36.9 μg m−3 in Chongqing (CQ), respectively. WSIIs contributed about 50% to PM2.5, and 90% of them were secondary inorganic ions. NH4+ and NO3− roughly followed the seasonal pattern of PM2.5 variations, whereas the highest levels of SO42− appeared in summer and autumn. PM2.5 samples were most acidic in autumn and winter, but were alkaline in spring. The aerosol acidity increased with the increasing level of anion equivalents. SO42− primarily existed in the form of (NH4)2SO4. Full neutralization of NH4+ to NO3− was only observed in low levels of SO42− + NO3−, and NO3− existed in various forms. SO42− and NO3− were formed mainly through homogeneous reactions, and there was the existence of heterogeneous reactions under high relative humidity. The main identified sources of WSIIs included coal combustion, biomass burning, and construction dust.
Highlights
Water-soluble inorganic ions (WSIIs) are a major part of fine particles (PM2.5, particulate matter with an aerodynamic diameter less than 2.5 μm)
± 36.9 μg m−3 in CQ, respectively. They all exceeded the latest NAAQS-II issued in 2012, and the annual PM2.5 concentrations were more than 2 times the 35 μg m−3 limit
Increasing NO3 − was observed in both Chengdu and Chongqing, which was probably due to the performance of desulfurization projects and elevated vehicular population
Summary
Water-soluble inorganic ions (WSIIs) are a major part of fine particles (PM2.5 , particulate matter with an aerodynamic diameter less than 2.5 μm). Secondary inorganic ions (SII), including sulfate (SO4 2− ), nitrate (NO3 − ), and ammonium (NH4 + ), are the predominant species and account for more than 90% of WSIIs [1]. Nationwide, SII contribute about 25%–48% to PM2.5 mass, and are attributable to about 60% of the visibility reduction in China [2]. They play important roles in atmospheric acidification and climate change [3,4]. Both homogeneous reaction via NO2 oxidation by OH radical and O3 , and the heterogeneous hydrolysis of N2 O5 on preexisting aerosols, are important pathways of nitric acid formation [8]
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