Stable carbon isotope evidence for origin of atmospheric polycyclic aromatic hydrocarbons in Zhengzhou and Urumchi, China

Origins of atmospheric polycyclic aromatic hydrocarbons (PAHs) in total suspended particulate (TSP) and particulate matter below 10 micrometers in diameter (PM10) collected in the urban areas of Urumchi and Zhengzhou, China, are discussed on the basis of carbon isotopic compositions of individual compounds. Carbon isotope ratios were measured with the system of GC-C-IRMS with an error (1σ) of less than 0.6‰. δ13C values of atmospheric PAHs in Urumchi range from –23.6‰ to –32.1‰ and from –22.5‰ to –31.0‰ in Zhengzhou. δ13C values of low-weight molecules (pyrene, fluoranthene, benzo[e]pyrene etc.) in PAHs from the two cities are concordant, and range from –23.0‰~–25.8‰. However, the high-weight individual compounds of atmospheric PAHs in Urumchi are more depleted in 13C with increasing molecular weight of PAHs than those in Zhengzhou. δ13C mean values of benzo[a]pyrene, indeno(1,2,3-cd)pyrene and benzo(ghi)perylene in Urumchi are –28.3‰, –31.5‰ and –29.7‰, respectively. The values of those three compounds in Zhengzhou, however, are –24.5‰, –29.4‰ and –26.3‰, respectively. Our data, incorporated with the analysis of the consumption of coal and amount of motor vehicles, indicate that PAHs are mainly contributed by coal combustion in the two cities, and the contribution of automobile exhaust to PAHs in Zhengzhou is larger than that in Urumchi during the sampling period.