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&plusmn;203 and 1728&plusmn;495 ng m⁻³ during winter and 1236&plusmn;335 and 1028&plusmn;193 ng m⁻³ during spring. EC in the urban and the suburban atmospheres were 17&plusmn;3.8 and 8.0&plusmn;2.1 μg m⁻³ during winter and 20&plusmn;5.9 and 7.1&plusmn;2.7 μg m⁻³ during spring, while OC at the urban and suburban sites were 74&plusmn;14 and 51&plusmn;7.9 μg m⁻³ in winter and 51&plusmn;20 and 23&plusmn;6.1 μg m⁻³ in spring. Secondary organic carbon (SOC) accounted for 38&plusmn;16% of OC in winter and 28&plusmn;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&plusmn;10 and 61&plusmn;27 μg m⁻³ in the urban air and 18&plusmn;7 and 32&plusmn;23 μg m⁻³ in the suburban air. A linear correlation (<i>r</i>²>0.8 in winter and <i>r</i>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 (<i>r</i>²>0.6) in winter, indicating an importance of emissions from coal burning for house heating. Stable carbon isotope compositions of TC (&delta;¹³C) became higher with an increase in the concentration ratios of C₂/OC due to aerosol aging. In contrast, nitrogen isotope compositions of TN (&delta;¹⁵N) became lower with an increases in the mass ratios of NH₄⁺/PM₁₀ and NO₃^&minus;/PM₁₀, which is possibly caused by an enhanced adsorption and/or condensation of gaseous NH₃ and HNO₃ onto particles.