Seasonal contributions to size-resolved n-alkanes (C₈-C₄₀) in the Shanghai atmosphere from regional anthropogenic activities and terrestrial plant waxes

Size-resolved aerosol samples from the Shanghai atmosphere were analyzed for normal alkanes (n-alkanes, C₈-C₄₀) by comprehensive two-dimensional gas chromatography-flame ionization detection and gas chromatography-triple quadruple mass spectroscopy to study their size distribution and contributions from potential regional sources based on a one-year (2012-2013) sampling campaign. The n-alkane concentrations ranged from 62.3 to 398.5ngm^-3, with an annual average of 227.6ngm^-3. Particle-associated n-alkanes exhibited a bimodal distribution with one peak in the accumulation-mode size range and the other in the coarse-mode size range. As the carbon number increased, the peak in the accumulation mode intensified and the peak in the coarse mode weakened, in accordance with variation of their corresponding volatilities. Source indices (carbon preference index, average chain length, odd-even carbon number preference, unresolved to resolved n-alkanes ratio, and plant wax n-alkanes ratio) indicated that the n-alkane source profile shifted from an anthropogenic-dominated pattern in winter and spring to a terrestrial plant wax-influenced pattern in summer and autumn. Further trajectory cluster analysis and potential source contribution function modeling showed that anthropogenic activities were mainly in the North China Plain and East China and that terrestrial plant waxes originated in Anhui, Zhejiang, and Jiangxi Provinces. The results of our study provide useful information for evaluating the influence of anthropogenic and biogenic activities on the atmospheric transport of important secondary organic aerosol precursors to megacities in East Asia.