Determination of n-alkanes, polycyclic aromatic hydrocarbons and hopanes in atmospheric aerosol: Evaluation and comparison of thermal desorption GC-MS and solvent extraction GC-MS approaches

Organic aerosol (OA) constitutes a large fraction of fine particulate matter (PM) in the urban air. However, the chemical nature and sources of OA are not well constrained. Quantitative analysis of OA is essential for understanding the sources and atmospheric evolution of fine PM, which requires accurate quantification of some organic compounds (e.g., markers). In this study, two analytical approaches, i.e., thermal desorption (TD) gas chromatography mass spectrometry (GC-MS) and solvent extract (SE) GCMS, were evaluated for the determination of n-alkanes, polycyclic aromatic hydrocarbons (PAHs) and hopanes in ambient aerosol. For the SE approach, the recovery obtained is 89.3 %-101.5 %, the limits of detection (LODs) are 0.05-1.1 ng (1.5-33.9 ngm^-3), repeatability is 3.5 %-14.5% and reproducibility is 1.2 %-10.9 %. For the TD approach, the recovery is 57.2 %-109.8 %, the LODs are 0.1-1.9 ng (0.04-0.9 ngm^-3), repeatability is 2.1 %-19.4% and reproducibility is 1.1 %-12.9 %. Ambient aerosol samples were collected from Beijing, Chengdu, Shanghai and Guangzhou during the winter of 2013 and were analyzed by the two methods. After considering the recoveries, the two methods show a good agreement with a high correlation coefficient (R² > 0.98) and a slope close to unity. The concentrations of n-alkanes, PAHs and hopanes are found to be much higher in Beijing than those in Chengdu, Shanghai and Guangzhou, most likely due to emissions from traffic and/or coal combustion for wintertime heating in Beijing.