Nitrate photolysis from snow can have a significant impact on the oxidative capacity of the local atmosphere, but the factors affecting the release of gas-phase products are not well understood. Here, we report a systematic study of the amounts of NO, NO2, and total nitrogen oxides (NOy) emitted from illuminated snow samples as a function of both nitrate and total salt (NaCl and Instant Ocean) concentration. The results provide experimental evidence that the release of nitrogen oxides to the gas phase is directly related to the expected nitrate concentration in the brine at the surface of the snow crystals. With no added salts, steady-state release of gas-phase products increases to a plateau value with increasing prefreezing nitrate concentration; with the addition of salts, the steady-state gas phase nitrogen oxides generally decrease with increasing prefreezing NaCl or Instant Ocean concentration. In addition, for these frozen mixed nitrate (25 mM) salt (0-500 mM) solutions, there is an increase in gas-phase NO2 seen at low added salt amounts, with NO2 production enhanced by up to 42% at low prefreezing [NaCl] (<= 25 mM) and by up to 89% at prefreezing Instant Ocean concentrations lower than 200 mM [Cl-]. This enhancement may be important to the atmospheric oxidative capacity in polar regions.
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机译：雪中硝酸盐的光解作用可能会对当地大气的氧化能力产生重大影响，但影响气相产物释放的因素尚不清楚。在这里，我们报告了从照明的雪样中排放出的NO，NO2和总氮氧化物（NOy）数量的系统研究，该数量与硝酸盐和总盐（NaCl和Instant Ocean）的浓度有关。结果提供了实验证据，表明氮氧化物向气相的释放与雪晶表面盐水中预期的硝酸盐浓度直接相关。在不添加盐的情况下，随着预冷冻硝酸盐浓度的增加，气相产物的稳态释放增加至平稳值。随着盐的加入，稳态气相氮氧化物通常会随着预冷冻NaCl或即刻海洋浓度的增加而降低。此外，对于这些冷冻的混合硝酸盐（25 mM）盐（0-500 mM）溶液，在低添加盐量下，气相NO2有所增加，而在低预冷冻下，NO2的产生增加了多达42％[ NaCl]（<= 25 mM），并且在预冻结即时海洋浓度低于200 mM [Cl-]时最多可达到89％。这种增强对于极性区域中的大气氧化能力可能很重要。
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