Characterization of size-resolved emissions of alkylated and nitrated polycyclic aromatic hydrocarbons (PAHs) from various combustion scenarios

Abstract

In this study, we examined the size-resolved emissions of alkylated and nitrated polycyclic aromatic hydrocarbons (alkyl- and nitro-PAHs) from various combustion sources including residential solid fuels, cigarette smoking, domestic waste burning, and vehicular exhausts, which have been scarcely addressed. The estimated emission factors (eEFs) of these PAH derivatives were generally highest from the biomass burning sources. Very few nitro-PAHs were detected in cigarette smoking, cooking, and vehicle emission sources. Significant linear or non-linear relationships were observed between methylated PAHs and their parent compounds; whereas the relationships were weak for most nitro-PAHs, revealing the difference and similarity in their emission or accumulation formation mechanisms. The size distributions of individual methylated phenanthrenes (PHEs) and PHE were very similar in each source, but different between the sources. Generally, in sources with higher eEFs, these compounds were more tendentious to associate with the fine fractions. The intra-source size distributions of the methylated naphthalenes (NAPs) and NAP were different in some sources. The cooking and vehicle sources showed the lowest distributions of these PAHs derivatives in fine particles. The size fractionations of nitro-PAHs among the sources were very variable due to the low emissions, except for a few high molecular weight compounds showing more robust enrichment in the fine fractions. In addition to the size-resolved characterization, this work also highlights the need for understanding their formation and fractionation mechanisms.