Photochemistry of Adsorbed Nitrate on Aluminum Oxide Particle Surfaces

Abstract

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 photochemistry 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 NO(2), NO, and N(2)O, with NO being the major product. The relative ratio and product yields of these gas-phase products change with RH, with N(2)O production being highest at the higher relative humidities. Furthermore, an efficient dark reaction readily converts the major NO product into NO(2) during post-irradiation. Photochemical processes on 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 on the renoxification of the atmosphere is discussed.

Thermal and photochemical oxidation of self-assembled monolayers on alumina particles exposed to nitrogen dioxide

“…[9][10][11][12][13][14] For example, it has long been recognized that NO 2 hydrolysis occurs on such surfaces to form surface nitrite and nitrate ions, 3,13,[15][16][17][18] both of which photolyze to generate OH radicals and NO or NO 2 . 17,[19][20][21][22][23] This chemistry leads to the release of highly photochemically labile gases such as HONO, a major OH source in the troposphere. [24][25][26][27] Consistent with the results of laboratory studies, increased HONO levels have been measured during dust storms.…”

Simulated atmospheric processing of iron oxyhydroxide minerals at low pH: Roles of particle size and acid anion in iron dissolution

“…Therefore, not all dissolved Fe(III) is expected to be present as free ions but in fact complexed and coordinated to anions in the deliquescent layer. Some of these complexes, as well as the inorganic anions themselves, can be photoactive (26,27), which may play a role in the overall dissolution process for Fe mobilization in sunlight. Furthermore, these anions can coordinate to the surface in different adsorption modes and with different bond strengths to the surface; this too will impact iron dissolution.…”

Thermal and photochemical reactions of NO2 on chromium(iii) oxide surfaces at atmospheric pressure

“…They also studied the photochemistry of nitrate ions formed on Al 2 O 3 by exposure to gaseous nitric acid followed by evacuation. 33,34,96,97 At the shortest irradiation times studied, NO 2 was the major gas-phase product at 20-80% RH, whereas NO dominated at RH o1%. This is similar to our observations of the interaction of NO 2 Since a significant amount of water vapor is present in the atmosphere, the heterogeneous reactions would be similar to our results under humid conditions.…”

“…In addition, N 2 O has been reported as a product in similar systems. 33,34 To determine if nitrogen oxides other than NO and NO 2 were present, the gaseous product mixtures at 10% and 50% RH were also examined by long-path FTIR. Using available absorption cross sections, 51,84 upper limits to the yields of gas-phase HONO and N 2 O relative to NO 2 were determined to be o2% and o6%, respectively.…”