Photochemistry of Adsorbed Nitrate

Abstract

In the atmosphere, gas-phase nitrogen oxides including nitric acid react with particle surfaces (e.g., mineral dust and sea salt aerosol) to yield adsorbed nitrate, yet little is known about the photochemistry of nitrate on the surface of these particles. In this study, nitrate adsorbed on alumina surfaces, a surrogate for mineral dust aerosol, is irradiated with broadband light (lambda > 300 nm) in the absence and presence of coadsorbed water, at <1% and 45 +/- 2% relative humidity (%RH), respectively, and molecular oxygen. Upon irradiation, the nitrate ion readily undergoes photolysis to yield nitrogen-containing gas-phase products, NO2, NO, and N2O. Although NO2, NO, and N2O form under the different conditions investigated, both coadsorbed water and molecular oxygen change the gas-phase product distribution, with NO being the major product under dry and humid conditions in the absence of molecular oxygen and NO2 the major product in the presence of molecular oxygen. To the best of our knowledge, this is the first study to investigate the role of solvation by coadsorbed water in the photochemistry of adsorbates at solid interfaces and the roles that molecular oxygen, adsorbed water, and relative humidity may have in photochemical processes on aerosol surfaces that have the potential to alter the chemical balance of the atmosphere.

Evidence for a nitrous acid (HONO) reservoir at the ground surface in Bakersfield, CA, during CalNex 2010

“…In other field observations, the photolysis of NO 3 À [Handley et al, 2007;Schuttlefield et al, 2008;Zhou et al, 2003;Zhou et al, 2011], photocatalytic conversion of NO 2 on humic and organic surfaces , or a link between measured NO 2 and surface irradiance [Wong et al, 2012] are suggested as likely pathways to HONO (g) daytime production. At most, 30% of the daytime HONO (g) source has been accounted for at the measurement height, dominated by the conversion of NO 2 on photoexcited humic acids [Sörgel et al, 2011b].…”

Photoreductive dissolution of Fe‐containing mineral dust particles in acidic media

“…Under such environment, not all Fe(III) is expected to be present as free ions; rather, inorganic ions present on the particle surface or in the homogeneous aqueous layer. These ions can be photoactive [ Schuttlefield et al , 2008; Hsu et al , 2007; Conklin and Hoffmann , 1988] and may have a significant effect on the overall dissolution process for Fe mobilization under sunlight. However, few measurements have been made of the photochemical properties of Fe(III) complexes with ligands other than hydrated Fe 3+ and FeOH 2+ , sometimes referred to by others as Fe(H 2 O) 6 3+ and FeOH(H 2 O) 5 2+ [ Miller et al , 1995; Kotronarou and Sigg , 1993].…”

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.…”