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Heterogeneous Oxidation of Benzo[a]pyrene: Kinetics, Products and Toxicity
AMY HRDINA, James Rowe, Simran Kaushal, Bevin Engelward, Jesse Kroll, MIT
Abstract Number: 208
Working Group: Aerosol Chemistry
Abstract
Polycyclic aromatic hydrocarbons (PAHs) are a class of chemical pollutants formed by incomplete combustion. PAHs are known carcinogens and mutagens; while atmospheric oxidation will degrade PAHs, it may also lead to the formation of toxic secondary products, modulating their health impacts in important but poorly understood ways. To better understand the rates and product of these degradation reactions, laboratory studies were conducted on the heterogeneous oxidation of particle-phase benzo[a]pyrene (BaP). BaP-coated ammonium sulfate aerosol particles were exposed to two common atmospheric oxidants, ozone (O3) and OH, in an environmental chamber. Reaction products and kinetics were investigated by measuring the evolving particle-phase composition with an Aerosol Mass Spectrometer (AMS). The reaction rate is described in terms of the uptake coefficient, the fraction of oxidant-particle collisions that lead to reaction; measured uptake coefficients of O3 and OH suggests atmospheric lifetimes of surface-bound BaP on the order of several hours, within the (very wide) range of previously reported values. The major products, observed by online AMS and offline liquid chromatography mass spectrometry (LCMS, operated in positive electrospray ionization mode), in both reaction systems include BaP-dione isomers (C20H12O2), 4-oxabenzo[d,e,f]chrysene-5-one (C19H10O2), and BaP epoxide or diol (C20H12O). The reaction with OH formed a higher yield of oxygenated compounds than the reaction with O3, suggesting OH reacts with both first- and second-generation products. However, such species account for only ~50% of the particulate products, with a large fraction of product species still unidentified. Preliminary toxicity studies of BaP coated aerosol particles were conducted using the high-throughput ‘CometChip’ assay to quantify DNA damage upon exposure to fresh versus oxidized BaP-coated aerosol particles.