Abstract
Abstract. Dicarboxylic acids (C2–C10), metals, elemental carbon (EC), organic carbon (OC), and stable isotopic compositions of total carbon (TC) and total nitrogen (TN) were determined for PM10 samples collected at three urban and one suburban sites of Baoji, an inland city of China, during winter and spring 2008. Oxalic acid (C2) was the dominant diacid, followed by succinic (C4) and malonic (C3) acids. Total diacids in the urban and suburban areas were 1546±203 and 1728±495 ng m−3 during winter and 1236±335 and 1028±193 ng m−3 during spring. EC in the urban and the suburban atmospheres were 17±3.8 and 8.0±2.1 μg m−3 during winter and 20±5.9 and 7.1±2.7 μg m−3 during spring, while OC at the urban and suburban sites were 74±14 and 51±7.9 μg m−3 in winter and 51±20 and 23±6.1 μg m−3 in spring. Secondary organic carbon (SOC) accounted for 38±16% of OC in winter and 28±18% of OC in spring, suggesting an enhanced photochemical production of secondary organic aerosols in winter under an inversion layer development. Total metal elements in winter and spring were 34±10 and 61±27 μg m−3 in the urban air and 18±7 and 32±23 μg m−3 in the suburban air. A linear correlation (r2>0.8 in winter and r2>0.6 in spring) was found between primary organic carbon (POC) and Ca2+/Fe, together with a strong dependence of pH value of sample extracts on water-soluble inorganic carbon, suggesting fugitive dust as an important source of the airborne particles. Polycyclic aromatic hydrocarbons (PAHs), sulfate, and Pb in the samples well correlated each other (r2>0.6) in winter, indicating an importance of emissions from coal burning for house heating. Stable carbon isotope compositions of TC (δ13C) became higher with an increase in the concentration ratios of C2/OC due to aerosol aging. In contrast, nitrogen isotope compositions of TN (δ15N) became lower with an increases in the mass ratios of NH4+/PM10 and NO3−/PM10, which is possibly caused by an enhanced adsorption and/or condensation of gaseous NH3 and HNO3 onto particles.
Highlights
Coal is a major energy source in China, accounting for around 70% of the total energy consumption
It should be noted that total carbon (TC) concentration was underestimated about 10% compared with that of (EC+organic carbon (OC)), which is resulted from the two different measurement methods (Kawamura et al, 2004)
A similar level of PM10 concentrations was observed in winter and spring, but pH of the water-extracted solution was lower in winter than in spring, indicating the wintertime PM10 is more acidic
Summary
Coal is a major energy source in China, accounting for around 70% of the total energy consumption. Very few studies have been performed for air pollution problems in western regions of China, which are characterized by semi-arid/arid climate, intensive usage of coal and relatively lower level of economic development. These situations cause the concentration levels of airborne particulate matter much higher than those in the coastal region of China (Shen et al, 2009; Wang et al, 2006a, b). Baoji is a mid-scale city (33◦35 ∼35◦06 N, 106◦18 ∼108◦03 E, population 0.8 million) located in the semi-arid region of Northwest China, where high loading of particles has been a persistent air pollution problem because of emissions from coal burning and dust. We report the chemical compositions of the PM10 samples (i.e. dicarboxylic acids, water-soluble inorganic and organic carbon, elemental and organic carbon, and metals) and their stable carbon and nitrogen isotopic compositions, and discuss the characteristics and sources of those airborne particulate matters in the inland region
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