Monotonic Increase of Nitrite Yields in the Photolysis of Nitrate in Ice and Water between 238 and 294 K

Abstract

The quantum yield, φ, of nitrite formation in the 302 nm band photolysis of fluid or frozen aqueous nitrate solutions increases monotonically with temperature over the range 238-294 K. The presence of formate increases φ 5-fold but does not modify its temperature dependence. Considering that the detection of nitrite as a product is only possible after the initial photofragments (NO 2 -+ O) escape the solvent cage and that the diffusivity of ice, D ice , is about 6 orders of magnitude smaller than that of supercooled water, D aq , at the same temperature, we infer that nitrate photodecomposition takes place in similar liquidlike media at all temperatures. We found that the nitrite dispersed into the bulk is subsequently degraded by OH radicals, another primary photoproduct that can be scavenged by formate. The fact that experimental φ values in ice are actually larger than those derived from linear φ vs D aq T 1/2 extrapolation of aqueous phase data, as expected for cage processes in homogeneous media, suggests that the photochemically relevant properties of the quasi-liquid layer covering ice below the normal melting point resemble those of bulk supercooled water, but other effects, such as the dissipation of excess photon energy into the medium, may also play a role.

Snow optical properties at Dome C (Concordia), Antarctica; implications for snow emissions and snow chemistry of reactive nitrogen

“…The temperature-dependant quantum yield of Reaction (R1a) on ice and the absorption cross-section of nitrate in aqueous solution are both taken from Chu and Anastasio (2003). The quantum yield reported in Chu and Anastasio (2003) broadly agrees with the work of Dubowski et al (2002) and is considered a good phenomological representation of the photolysis of nitrate in snow and ice. Other available quantum yield data for 308 nm photolysis of nitric acid on ice films of 0.92 ± 0.26 (Zhu et al, 2010) seem extremely high compared with previous data (Warneck and Wurzinger, 1988;Zellner et al, 1990;Dubowski et al, 2002;Chu and Anastasio, 2003), but if correct would potentially increase the NO 2 production by a factor of ∼400.…”

The impact of parameterising light penetration into snow on the photochemical production of NO<sub><i>x</i></sub> and OH radicals in snow

“…and NO − 2 in snow and ice contribute to the formation of OH radicals within the snowpack (Dubowski et al, 2001(Dubowski et al, , 2002Cotter et al, 2003;Chu and Anastasio, 2003;Anastasio and Chu, 2008) through reaction of oxygen radical anion (O − ) with water (Reaction R6).…”

Reactions at surfaces in the atmosphere: integration of experiments and theory as necessary (but not necessarily sufficient) for predicting the physical chemistry of aerosols

“…154 Much of this appears to be driven by photochemistry of oxides of nitrogen, particularly nitrate ions. 140,141,144,145,[345][346][347][348] While there are likely some commonalities between the chemistry of heterogeneous nitrogen oxide reactions on tropospheric surfaces at room temperature and that in and on ice, the linkage needs further work to elucidate the relationships between the two.…”