Abstract:

To understand chemical characteristics and sources of $n$-alkanes and hopanes in the atmospheric PM$_{2.5}$ in Yiwu City, a representative county-level city in the Yangtze River Delta region, seasonal atmospheric PM$_{2.5}$ samples were collected smultaneously at two sites in Yiwu City, Beiyuan and Jiangdong, from July 2015 to April 2016 using TH-16A four-channel samplers. Concentrations of $n$-alkanes (C$_{16}\sim $C$_{34})$ and hopanes (C$_{27}\sim $C$_{32})$ in the PM$_{2.5}$ samples were quantified with gas chromato graphy-mass spectrometer (GC-MS). The results show that the annual average concentration of $n$-alkanes in PM$_{2.5}$ at Beiyuan and Jiangdong were 78.0 and 80.4 ng/m$^{3}$, respectively. No statistical difference in concentration of $n$-alkanes was found between the two sampling sites. A distinct seasonal trend of winter$\to $autumn$\to $spring$\to $summer was found for $n$-alkanes in Yiwu City. The distribution patterns, carbon number maxima (C$_{\max})$, carbon preference index (CPI) and plant wax contribution (Wax${\%}$) of $n$-alkanes all indicated that emissions from fossil-fuel usage was the main source of $n$-alkanes in PM$_{2.5}$ in Yiwu City, while the average contribution of plant wax was about 20${\%}$. The annual average concentration of hopanes in PM$_{2.5}$ at Beiyuan and Jiangdong were 5.5 and 4.6 ng/m$^{3}$, respectively. Strong correlation between the concentrations of hopanes and $n$-alkanes was found. The distribution pattern and characteristics of hopanes indicated that vehicle emission was an important source of the organic matter in PM$_{2.5}$ in Yiwu City.

Key words: PM$_{2.5}$, $n$-alkanes, hopanes, source identification, Yangtze River Delta, Yiwu City