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

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.