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-2-C-10), 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 (C-2) was the dominant diacid, followed by succinic (C-4) and malonic (C-3) 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 mu g m(-3) during winter and 20 +/- 5.9 and 7.1 +/- 2.7 mu gm(-3) during spring, while OC at the urban and suburban sites were 74 +/- 14 and 51 +/- 7.9 mu g m(-3) in winter and 51 +/- 20 and 23 +/- 6.1 mu g 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 mu g m(-3) in the urban air and 18 +/- 7 and 32 +/- 23 mu g m(-3) in the suburban air. A linear correlation (r(2) > 0.8 in winter and r(2) > 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 (r(2) > 0.6) in winter, indicating an importance of emissions from coal burning for house heating. Stable carbon isotope compositions of TC (delta C-13) became higher with an increase in the concentration ratios of C-2/OC due to aerosol aging. In contrast, nitrogen isotope compositions of TN (delta N-15) 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.