Characteristics and Sources of Water-Soluble Ions in PM2.5 in the Sichuan Basin, China

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.

Water-soluble ions and source apportionment of PM2.5 depending on synoptic weather patterns in an urban environment in spring dust season

“…A study performed in Heze, China 44 showed that ions mainly exist in the form of NH 4 NO 3 , NH 4 HSO 4 , and (NH 4 ) 2 SO 4 in winter and autumn, and the forms were more complex and diverse in spring and summer. Chen et al found that in Sichuan, China, the content of NH 4 + in most samples during spring was sufficient to neutralize SO 4 2 and NO 3 − to form (NH 4 ) 2 SO 4 and NH 4 NO 3 45 . A study in southeastern Italy 46 indicated there was a strong correlation between SO 4 2- and NH 4 + , with the ammonium salt in the form of ammonium sulfate.…”

Meteorological Influence and Chemical Compositions of Atmospheric Particulate Matters in an Indian Urban Area

“…The anion equivalence and cation equivalence ratio (AE/CE) can be measured to determine the acidity of PM 2.5 , which can be calculated using the equations below …”

Chemical Characteristics of PM2.5 and Water-Soluble Organic Nitrogen in Yangzhou, China

“…It is important to note that NO 2 − concentration was below the detection limit and was, therefore, not included in Equation (9). The scatter plot between CE and AE is presented in Figure 6b.…”

“…In particular, much effort has been devoted to the study of fine particles with an aerodynamic diameter less than 2.5 µm (PM 2.5 ) due to its adverse health effects. Along with rapid economic growth, PM 2.5 pollution events ('haze') have occurred frequently in China, and many studies have been carried out to elucidate the properties of PM 2.5 , especially in densely populated regions [4][5][6][7][8][9]. However, the chemical composition of PM 2.5 is highly complex, possibly containing a wide variety of components, including inorganic salts (nitrate, sulfate, and ammonium), trace metals, elemental carbon, and a large number of organic species.…”