Reactive Uptake of NO sub(3), N sub(2)O sub(5), NO sub(2), HNO sub(3), and O sub(3) on Three Types of Polycyclic Aromatic Hydrocarbon Surfaces

We investigated the reactive uptake of NO sub(3), N sub(2)O sub(5), NO sub(2), HNO sub(3), and O sub(3) on three types of solid polycyclic aromatic hydrocarbons (PAHs) using a coated wall flow tube reactor coupled to a chemical ionization mass spectrometer. The PAH surfaces studied were the 4-ring systems pyrene, benz[a]anthracene, and fluoranthene. Reaction of NO sub(3) radicals with all three PAHs was observed to be very fast with the reactive uptake coefficient, gamma, ranging from 0.059 (+0.11/-0.049) for benz[a]anthracene at 273 K to 0.79 (+0.21/-0.67) for pyrene at room temperature. In contrast to the NO sub(3) reactions, reactions of the different PAHs with the other gas-phase species (N sub(2)O sub(5), NO sub(2), HNO sub(3), and O sub(3)) were at or below the detection limit (gamma < 6.6 x 10 super(-5)) in all cases, illustrating that these reactions are at best slow. For NO sub(3) we also investigated the time dependence of the reactive uptake to determine if the surface-bound PAH molecules were active participants in the reaction (i.e., reactants). Reaction of NO sub(3) on all three PAH surfaces slowed down at 263 K after long NO sub(3) exposure times, suggesting that the PAH molecules were reactants. Additionally, NO sub(2) and HNO sub(3) were identified as major gas-phase products. Our results show that under certain atmospheric conditions, NO sub(3) radicals can be a more important sink for PAHs than NO sub(2), HNO sub(3), N sub(2)O sub(5), or O sub(3) and impact tropospheric lifetimes of surface-bound PAHs.