Abstract View
OH Formation during the Photolysis of Polycyclic Aromatic Hydrocarbons
HEATHER RUNBERG, Brian Majestic, University of Denver
Abstract Number: 448
Working Group: Aerosol Chemistry
Abstract
Polycyclic aromatic hydrocarbons (PAH) are a ubiquitous atmospheric pollutant, comprising up to 50% of combustion particles. They undergo rapid photo-oxidation to form oxidized PAH products (oxPAH), and eventually, humic-like substances (HULIS). The primary goal of this study was to elucidate the role of hydroxyl radical (OH) formation along the HULIS formation pathway in atmospherically relevant conditions. To do this, anthracene (ANT) and a selection of oxPAH (1-naphthol, 2-naphthol, 1,4-naphthaquinone, 1,4-anthraquinone, and 9,10-anthraquinone) were exposed to simulated sunlight for 16 hours and OH concentration was measured at various time points. OH formation from ANT after a 16-hour reaction was 8.5 ± 0.1 µM OH per mM of starting material. Of the selected oxPAH, 1,4-naphthaquinone (NAPQ) generated the most OH, at 10.0 ± 0.2 µM OH per mM of starting material, significantly more than was seen with ANT.
Additionally, OH formation was measured every five minutes for the first 30 minutes of a 16-hour reaction; incremental formation rates were calculated at each timepoint. NAPQ had an incremental rate at five minutes of 1.10 ± 0.01 µM min-1. The rate steadily declined over the next 25 minutes, with an incremental rate at 30 minutes of 0.28 ± 0.1 µM min-1. Conversely, the OH formation rate during the first 30 minutes of the ANT reaction showed an initial OH burst with a relatively high incremental rate at five minutes of 0.09 ± 0.01 µM min-1, followed immediately by a significantly lower incremental rate of 0.03 ± 0.01 µM min-1 at 10 minutes. The incremental rate then steadily increased over the next 25 minutes, with a rate at 30 minutes of 0.12 ± 0.01 µM min-1, suggesting that NAPQ is driving OH formation during the photo-oxidation of ANT.