Determination of anhydride in atmospheric fine particles by optimized solvent extraction

Anhydrides are a class of oxygenated-PAHs commonly found in the atmosphere and tend to cause respiratory sensitization in humans. They are mainly formed by the photochemical reaction of polycyclic aromatic hydrocarbons (PAHs) with hydroxyl radicals and ozone during the daytime. However, there is significant uncertainty about the accurate quantification used by methanol in solvent extraction. In this study, anhydrides react with methanol and the degree of reaction varies among different structures. The concentration of phthalic anhydride (PA) could decrease for 80% in the presence of methanol, while 1,8-naphthalic anhydride (1,8-NA) was not muchly alcoholized. Moreover, the methanolysis products of PA undergo thermal decomposition at the gas chromatography (GC) inlet, which affects the detection results of the alcoholysis reaction. Five anhydrides were detected and quantified by gas chromatography-mass spectrometry (GC-MS) in atmospheric fine particulate matter (PM2.5) collected in suburban Beijing, China, during the winter heating period in 2017. 3-Methylphthalic anhydride and 4-methylphthalic anhydride was detected for the first time. The carbon content of these anhydrides accounted for 0.40% of secondary organic carbon (SOC). This study reports some difficulties encountered in the solvent extraction and GC analysis, which aims to enrich the understanding of anhydrides in PM2.5.