Dicarboxylic acids, metals and isotopic compositions of C and N in atmospheric aerosols from inland China: implications for dust and coal burning emission and secondary aerosol formation

Dicarboxylic acids (C<sub>2</sub>–C<sub>10</sub>), metals, elemental carbon (EC), organic carbon (OC), and stable isotopic compositions of total carbon (TC) and total nitrogen (TN) were determined for PM<sub>10</sub> samples collected at three urban and one suburban sites of Baoji, an inland city of China, during winter and spring 2008. Oxalic acid (C<sub>2</sub>) was the dominant diacid, followed by succinic (C<sub>4</sub>) and malonic (C<sub>3</sub>) acids. Total diacids in the urban and suburban areas were 1546±203 and 1728±495 ng m<sup>−3</sup> during winter and 1236±335 and 1028±193 ng m<sup>−3</sup> during spring. EC in the urban and the suburban atmospheres were 17±3.8 and 8.0±2.1 μg m<sup>−3</sup> during winter and 20±5.9 and 7.1±2.7 μg m<sup>−3</sup> during spring, while OC at the urban and suburban sites were 74±14 and 51±7.9 μg m<sup>−3</sup> in winter and 51±20 and 23±6.1 μg m<sup>−3</sup> 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<sup>−3</sup> in the urban air and 18±7 and 32±23 μg m<sup>−3</sup> in the suburban air. A linear correlation (<i>r</i><sup>2</sup>>0.8 in winter and <i>r</i><sup>2</sup>>0.6 in spring) was found between primary organic carbon (POC) and Ca<sup>2+</sup>/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 (<i>r</i><sup>2</sup>>0.6) in winter, indicating an importance of emissions from coal burning for house heating. Stable carbon isotope compositions of TC (δ<sup>13</sup>C) became higher with an increase in the concentration ratios of C<sub>2</sub>/OC due to aerosol aging. In contrast, nitrogen isotope compositions of TN (δ<sup>15</sup>N) became lower with an increases in the mass ratios of NH<sub>4</sub><sup>+</sup>/PM<sub>10</sub> and NO<sub>3</sub><sup>−</sup>/PM<sub>10</sub>, which is possibly caused by an enhanced adsorption and/or condensation of gaseous NH<sub>3</sub> and HNO<sub>3</sub> onto particles