Characterization of organic aerosols from a Chinese Mega-City during winter: predominance of fossil fuel combustion

Abstract. PM2.5 aerosol samples were collected in a typical mega-city in China (Nanjing: 32.21° N and 118.73° E) during winter and analyzed for more than 100 compounds of twelve organic compound classes. The most abundant classes of compounds are n-alkanes (average, 205 ng m−3), followed by fatty acids (76.3 ng m−3), polycyclic aromatic hydrocarbons (PAHs) (64.3 ng m−3), anhydro-sugars (56.3 ng m−3), fatty alcohols (40.5 ng m−3), and phthalate esters (15.2 ng m−3), whereas hydroxy-/polyacids (8.33 ng m−3), aromatic acids (7.35 ng m−3), hopanes (4.19 ng m−3), primary sugars and sugar alcohols (4.15  ng m−3), lignin and resin products (2.94 ng m−3), and steranes (2.46 ng m−3) are less abundant. The carbon preference index of n-alkanes (0.83–1.38) indicated that they were mainly derived from the incomplete combustion of fossil fuels. Diagnostic concentration ratios of organic tracers suggested that PAHs and hopanes are mostly originated from coal burning and traffic emissions, respectively in Nanjing urban area. Positive matrix factorization analysis demonstrated that fossil fuel combustion is the dominant source (28.7 %) in Nanjing winter aerosols. Most of the compounds generally showed higher concentrations in nighttime than in daytime, due to the accumulation process associated with the inversion layers and increased emissions from heavy-duty trucks at night. We conclude that fossil fuel combustion largely influences the winter organic aerosols in urban Nanjing area. Based on the comparison of present results with previous studies, we found that pollution levels on organic aerosols have been decreased in the urban Nanjing atmosphere for the last decade.