Atmospheric Heterogeneous Reactions of Benzo(a)pyrene

This experimental study deals with heterogeneous reactions of benzo(a)pyrene (BaP) with ozone, nitrogen dioxide and hydroxyl radicals. BaP was adsorbed on silica particles chosen here as a model of mineral atmospheric particles. Compound extractions were assisted by focused microwave and analyses were performed by gas chromatography coupled with mass spectroscopy in single ion monitoring mode. Pseudo-first order rate constants were obtained from the fit of experimental decays of particulate-BaP concentration versus reaction time. Second order rate constants were determined considering the different oxidant gaseous concentrations except for the case of hydroxyl radicals where only a pseudo-first order rate constant was proposed. Values obtained at room temperature are (2.1±0.5)×10 −15 cm 3 molecule −1 s −1 for (BaP + ozone), (5.8±1.4)×10 −16 cm 3 molecule −1 s −1 for (BaP + nitrogen dioxide) and (3.4±0.8)×10 −2 s −1 for (BaP + OH) reactions. Products have only been investigated for the NO 2 and the OH (in the presence of NO x ) reactions. 1-, 3- and 6-nitrobenzo(a)pyrenes were detected as degradation products and quantified. Reaction rate constants for product formation are (3.7±0.9)×10 −16 cm 3 molecule −1 s −1 for 6-NBaP, (2.2±0.6)×10 −17 cm 3 molecule −1 s −1 for 1-NBaP and (5.3±1.3)×10 −17 cm 3 molecule −1 s −1 for 3-NBaP. 1-, 3- and 6-nitroBaP account respectively for approximately 5%, 12% and 83% of total nitrated species. If in the presence of only nitrogen dioxide, BaP was totally degraded within few minutes, only 20 to 25 % of the initial BaP led to nitrated compounds when reacting with OH (in the presence of NO x ).