Temperature and wavelength dependence of nitrite photolysis in frozen and aqueous solutions

While the photolysis of nitrite is an important source of hydroxyl radical (center dot 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 center dot OH from the photolysis of frozen and aqueous NO2-. From our solution and ice results, we derive a master equation that describes the center dot OH quantum yield from NO2- photolysis as a function of both temperature (240-295 K) and illumination wavelength (302-390 nm): Phi(NO2- -> OH center dot)(T,lambda) = (gamma(0) + a/(1 + exp((lambda - c)/b)))exp-(((e lambda + f)/R) x (1/295 - 1/T)) where gamma(0) = 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, T is the temperature (K), R is the gas constant (8.314 J mol(-1) K-1), and lambda 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 center dot OH.