What controls photochemical NO and NO2 production from Antarctic snow? Laboratory investigation assessing the wavelength and temperature dependence

[1] Laboratory experiments were conducted to determine the wavelength and temperature dependence of NO and NO2 release from Antarctic snow. This photochemically driven process has been observed during recent field measurements in polar regions. In this work the photochemical production of NO and NO2 was reproduced under laboratory conditions with NO2 dominating the production. The wavelength of incident light was varied over the range 295-385 nm. We observed a lambda dependence where NO and NO2 release ceases when the snow was illuminated with lambda > 345 nm. Comparing these data with the aqueous absorption cross section of the nitrate ion (NO3-) indicates that NO3- is the precursor N-oxide species, which is photolyzed in snow. The temperature of the experimental system was varied over the range 253-243 K with no effect on NO and NO2 production. The occurrence of these photochemical processes followed by release to the atmosphere will impact the chemistry of the boundary layer over any snow-covered region. In addition, understanding these processes is essential for accurate ice core interpretation.