Particulate Size Distribution and Sources Evaluation of n-Alkanes during Long-Term Haze Episode around Chaohu Lake, Eastern

Qiu-Ping Xu, Ji-Zhong Wang , Jia-Qin Liu, Shu-Chuan Peng

Abstract

n-Alkanes (from nC16 to nC32) associated with particulate matters were determined in the ambient air around Chaohu Lake, Eastern China, from October to December in 2014 during a long-term haze episode. The total concentrations of particle bounded n-alkanes varied from 332 to 2500 ng m–3, with the homologues of nC24–nC30 the most abundant species. Spatial analysis revealed that low concentrations of n-alkanes existed at the sites close to Chaohu Lake, while high concentrations were generally at locations distant from the lake. For all aggregated fractions, most n-alkanes were distributed in fine particles with the mean geometric mean diameter (GMD) varying from 3.0 ± 0.6 µm for nC16 to 2.1 ± 0.6 µm for nC32. Short chain n-alkanes were accumulated in coarse particles with a unimodal distribution, but long chain aliphatic hydrocarbons appeared to have a biomodal distribution in fine and coarse particles. The mass size distribution of individual n-alkane homologue was predominantly influenced by its volatility; thus GMDs were well correlated with the logarithmically transformed subcooled liquid vapor pressures (PLo, Pa) of n-alkanes at each sampling site, following the equation: GMDs = mgLogPLo + bg. Furthermore, mg and bg obtained from all locations tended to exhibit a significant linear correlation. This suggests that all saturated aliphatic hydrocarbons follow a similar accumulation mode during a haze episode, which allows us to predict the size distribution and GMD of a compound based on its PLo.
Keywords: Chaohu Lake n-alkanes particulate matter size distribution geometric mean diameter

Source: nbsp; Volume: 17 , Issue: 8 , Pages: 1975-1984 DOI: 10.4209/aaqr.2017.05.0189