Temperature and Wavelength Dependence of Nitrite Photolysis in Frozen and Aqueous Solutions

Abstract

While the photolysis of nitrite is an important source of hydroxyl radical (*OH) in some natural waters, its wavelength and temperature dependence have not been fully described in solution. In addition, there are no studies of this reaction on ice, although there is evidence of nitrite production in snow. To address these gaps, we have measured the wavelength and temperature dependence of the quantum yields of *OH from the photolysis of frozen and aqueous NO2-. From our solution and ice results, we derive a master equation that describes the *OH quantum yield from NO2 photolysis as a function of both temperature (240-295 K) and illumination wavelength (302-390 nm): phi(NO1- -->OH*)(T,lamda) = (Y0 + a/(1 + exp((lamda-c)/b)))exp-(((e lamda) + f)/R) x (1/295 - 1/T)) where Y0 = 0.0204 +/- 0.0010, a = 0.0506 +/- 0.0022, b = 11.2 +/- 1.2, c = 332 +/- 1, e = 20.5 +/- 3.2, f = 7553 +/- 1204, uncertainties represent 1 standard error, Tis the temperature (K), Ris the gas constant (8.314 J mol(-1) K(-1)), and lamda is the wavelength (nm). Using these results we predict the pseudo-steady-state concentrations of nitrite on sunlit polar snow grains and compare the relative importance of the photolysis of nitrite, nitrate, and hydrogen peroxide as sources of snow-grain *0H.

Chemistry of the Antarctic Boundary Layer and the Interface with Snow: an overview of the CHABLIS campaign

“…However, the results do illustrate that, at least at Halley, nitrite, albeit at low concentrations in the snow, can be a very significant source of NO x . This conclusion, arrived at from measurements, agrees with that of Chu and Anastasio (2007) who made this suggestion based on calculations. What it means is that numerical models that aim to calculate fluxes of NO x from snow (and indeed those probing the chemistry of snow-pack and its interstitial air) should include a comprehensive suite of reactions to account for nitrite formation and subsequent photolysis.…”

“…Jacobi and Hilker (2007) used a model derived from laboratory experiments and applied it to field data to calculate nitrite concentrations in summertime snow at Summit, Greenland, of less than 0.0002 nM. Chu and Anastasio (2007) calculated concentrations of snow grain nitrite based on steady state analysis of sources and sinks for four polar locations. Their estimates ranged from 0.7 nM (for Alert) to 13 nM (for Summit).…”

“…The interest in comparing nitrite and nitrate snow pack concentrations stems from the fact that both are potential sources of OH (although their direct contribution has been shown to be considerably less than that from H 2 O 2 for example (Chu and Anastasio, 2007), and also sources of NO x . Nitrate is photolysed to directly produce NO 2 via its major channel:…”

“…Comparing photolysis rates, surface snow concentrations (measured at the surface of the snowpits), and the consequent ratio in NO x production rate from nitrite and nitrate in snow. The photolysis rates are for j (NO − 2 →NO) and j (NO − 3 →NO 2 ) respectively for noon 21 December conditions (Chu and Anastasio, 2007 Some models calculate actinic flux from first principles, and so include a comprehensive treatment of up-welling actinic flux, including the calculation of Rayleigh scattering and 2A cos(SZA) together with multiple reflections between cloud and snow. These models need the albedo A as an input.…”

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.…”