310 nm Irradiation of Atmospherically Relevant Concentrated Aqueous Nitrate Solutions: Nitrite Production and Quantum Yields

Abstract

The heterogeneous processing of atmospheric aerosols by reaction with nitrogen oxides results in the formation of particulate and adsorbed nitrates. The water content of these hygroscopic nitrate aerosols and consequently the nitrate ion concentration depend on relative humidity, which can impact the physicochemical properties of these aerosols. This report focuses on the 310 nm photolysis of aqueous sodium and calcium nitrate solutions at pH 4 over a wide concentration range of nitrate ion concentrations representative of atmospheric aerosols. In particular, the quantum yield (phi) of nitrite formation was measured and found to significantly decrease at high concentrations of nitrate for Ca(NO(3))(2). In particular, phi for Ca(NO(3))(2) was found to have a maximum value of (7.8 +/- 0.1) x 10(-3) for nitrate ion solution concentrations near one molal, with the smallest quantum yield for the highest concentration solution above 14 m nitrate ion, phi = (2.3 +/- 2.0) x 10(-4). The effect of the addition of the radical scavenger, formate, on the 310 nm photolysis of these solutions was also investigated and found to increase phi by a factor of 2 or more for both sodium and calcium nitrate solutions. In the presence of formate, Ca(NO(3))(2) solutions again showed a significant decrease in phi with increasing NO(3)(-) concentration: phi = (1.4 +/- 0.1) x 10(-2) at (1.0 +/- 0.1) x 10(-2) m NO(3)(-) compared to phi = (4.2 +/- 0.3) x 10(-3) at 14.9 +/- 0.1 m NO(3)(-). This decrease in phi was not observed in NaNO(3) solutions. The change in electronic structure, as evident by the more pronounced shift of the n-pi* absorption band away from actinic wavelengths with increasing concentration for Ca(NO(3))(2) compared to NaNO(3), is most likely the origin of the greater decrease in phi for Ca(NO(3))(2) compared to NaNO(3) at elevated NO(3)(-) concentrations. The role of nitrate photochemistry in atmospheric aerosols and the atmospheric implications of these concentration dependent quantum yields are discussed.

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

“…For example, Grassian and coworkers observed a shift in the absorption spectra of NaNO 3 and Ca(NO 3 ) 2 as a function of concentration, and the quantum yield for photolysis of Ca(NO 3 ) 2 was also shown to decrease with increasing salt concentration. 186,187 Because photolysis of nitrite ions generates OH radicals, reaction (11) above, similar oxidation of adsorbed organics would be expected during irradiation of particles containing NO 2 À , and this has indeed been observed. 188,189 In this case, a phosopholipid, 1-oleoyl-2-palmitoyl-sn-glycero-3-phosphocholine (OPPC), was adsorbed on a dilute (0.4 wt%) NaNO 2 /NaCl salt solid mixture and the loss of nitrite and OPPC and the formation of organic products followed with time using diffuse reflection infrared Fourier transform spectrometry (DRIFTS).…”

Photochemistry of single particles using acoustic levitation coupled with Raman microspectrometry

“…A first experiment was conducted on levitated sodium nitrate (NaNO 3 ) containing particles. The photolysis of aqueous nitrate ions has been the subject of detailed investigations and constitutes a source of nitrite (NO 2 − ) ions and radicals in the environment …”

Solar disinfection is an augmentable, in situ -generated photo-Fenton reaction—Part 1: A review of the mechanisms and the fundamental aspects of the process

“…On the other hand, these reactions, or similar ones with bromine could potentially lead to halogenated by-products. Furthermore, the production of • has been linked with nitrite and nitrate photoreactions [383,384]. The reaction scheme is as follows [385]: Also, photolysis of nitrogen-containing DOM is found to produce nitrite, as well as nitrate photolysis [369].…”