Nitrogen Dioxide Release in the 302 nm Band Photolysis of Spray-Frozen Aqueous Nitrate Solutions. Atmospheric Implications

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 105; no. 20; pp. 4928 - 4932
• Main Authors: Dubowski, Yael, Colussi, A. J, Hoffmann, M. R
• Format: Journal Article
• Language: English
• Published: American Chemical Society 24.05.2001
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp0042009

We quantify the NO2 fluxes released into the gas phase during the continuous λ ∼ 300 nm photolysis of NO3 - in submillimeter ice layers produced by freezing aqueous KNO3 sprays on cold surfaces. Fluxes, F NO 2 , increase weakly with [NO3 -] between 5 ≤ [NO3 -]/mM ≤ 50 and increase markedly with temperature in the range of 268 ≥ T/K ≥ 248. We found that F NO 2 , the photostationary concentration of NO2 - (another primary photoproduct), and the quantum yield of 2-nitrobenzaldehyde in situ photoisomerization are nearly independent of ice layer thickness d within 80 ≤ d/μm ≤ 400. We infer that radiation is uniformly absorbed over the depth of the ice layers, where NO3 - is photodecomposed into NO2 (+ OH) and NO2 - (+ O), but that only the NO2 produced on the uppermost region is able to escape into the gas phase. The remainder is trapped and further photolyzed into NO. We obtain φNO 2 − ∼ 4.8 × 10-3 at 263 K, i.e., about the quantum yield of nitrite formation in neutral NO3 - aqueous solutions, and an apparent quantum yield of NO2 release φ‘NO 2 ∼ 1.3 × 10-3 that is about a factor of 5 smaller than solution φOH data extrapolated to 263 K. These results suggest that NO3 - photolysis in ice takes place in a liquidlike environment and that actual φ‘NO 2 values may depend on the morphology of ice deposits. Present φ‘NO 2 data, in conjunction with snow albedo and absorptivity data, lead to FNO 2 values in essential agreement with recent measurements in Antarctic snow under solar illumination.