Heterogeneous ozonolysis of alkyl substituted-polycyclic aromatic hydrocarbons (AlkPAHs) in the atmosphere†

Abstract

Polycyclic aromatic compounds (PACs) encompass a range of organic pollutants, including polycyclic aromatic hydrocarbons (PAHs), alkyl-substituted PAHs (AlkPAHs), and others. PAHs have been extensively studied due to their environmental and health implications. AlkPAHs, however, have received relatively less attention, despite recent evidence suggesting their greater abundances in ambient air. Given their prevalence and potential risks, investigating the atmospheric transformation of AlkPAHs is crucial. This work focuses on the heterogeneous oxidation of AlkPAHs, specifically addressing the influence of alkyl groups on reaction kinetics. Oxidation by gas phase ozone was conducted on quartz filters, which serve as models for silica surfaces on which PACs can deposit with minimal chemical interactions. The results reveal that AlkPAHs react faster with ozone than PAHs do, with reaction rates increasing with higher alkyl group substitutions. Furthermore, oxygenated polycyclic aromatic hydrocarbons (OPAHs) were formed during the oxidation of 1-methylpyrene, with greater diversity than those from pyrene. These products are more polar and potentially more toxic than parent compounds. In conclusion, this research advances our understanding of PAC oxidation, focusing on AlkPAHs' heterogeneous oxidation, the influence of alkyl groups, and the formation of OPAHs. These insights have significant implications for air quality, health risk assessments, and the fate of PACs in the environment.