Photochemistry of Adsorbed Nitrate on Aluminum Oxide Particle Surfaces

Nitrogen oxides, including nitrogen dioxide and nitric acid, react with mineral dust particles in the atmosphere to yield adsorbed nitrate. Although nitrate ion is a well-known chromophore in natural waters, little is known about the surface photochernistry of nitrate adsorbed on mineral particles. In this study, nitrate adsorbed on aluminum oxide. a model system for mineral dust aerosol, is irradiated with broadband light (lambda > 300 nm) as a function of relative humidity (RH) in the presence of molecular oxygen. Upon irradiation, the nitrate ion readily undergoes photolysis to yield nitrogen-containing gas-phase products including NO2, NO, and N2O, with NO being the major product. The relative ratio and product yields of these gas-phase products change with RH, with N2O production being highest at the higher relative humidities. Furthermore, an efficient dark reaction readily converts the major NO product into NO2 during post-irradiation. Photochemical processes oil mineral dust aerosol surfaces have the potential to impact the chemical balance of the atmosphere, yet little is known about these processes. In this study, the impact that adsorbed nitrate photochemistry may have oil the renoxification of the atmosphere is discussed.