Benzene polycarboxylic acid characterisation of polyaromatics in ambient aerosol: Method development

Abstract

Studies on pollution due to polyaromatics (PAs) focus on a limited number of commercially available compounds such as US-EPA priority polycyclic aromatic hydrocarbons (EPA-PAHs). Benzene polycarboxylic acid (BPCA) method involves oxidation of condensed aromatic rings (CARs) to a few BPCAs, and the subsequent conversion of the BPCA carbon to CAR carbon. It can be used to quantify PAs in environmental samples (in terms of CAR carbon), although the chemical structures of numerous PAs are still unknown. However, this method needs to be developed further for practical application. In this study, we developed a protocol for the simultaneous analysis of EPA-PAHs, and characterisation of low- and high-polarity PAs in aerosols by the BPCA method, using an aerosol reference material. The low- and high-polarity PAs were extracted successively with dichloromethane and water. A gas chromatography-mass spectrometry (GC-MS) method was developed for the BPCA characterisation of PAs in aerosol. Chromatographic peaks of BPCAs could be identified easily and reliably with a short instrumental runtime (18.2 min). Deuterated phenanthrene was first used as a surrogate of chemicals characterised by the BPCA method, which significantly improved the reproducibility of the method (mean coefficient of variation ∼4%). Particles that remain in the solvent extracts may contain chemicals with highly condensed aromatic structures, resulting in the overestimation of PAs quantified by the BPCA method. This situation was investigated by analysing BPCA patterns, and the particles that remained were found to be negligible through appropriate extraction techniques. Preliminary results from the analysis of the aerosol reference material using the protocol revealed that EPA-PAHs account for less than 1% of low-polarity PAs. The abundance of low- and high-polarity PAs was found to be comparable, whereas there is very little knowledge on the sources, pollution, and health effects of high-polarity PAs in ambient aerosol at present.