Department of Chemistry, University of California, Irvine, California 92697-2025, United States.
Environ Sci Technol. 2012 Oct 2;46(19):10447-54. doi: 10.1021/es300607c. Epub 2012 May 1.
Nitrate and halide ions coexist in a number of environmental systems, including sea salt particles, the Arctic snowpack, and alkaline dry lakes. However, little is known about potential synergisms between halide and nitrate ions. The effect of sea salt on NO(3)(-) photochemistry at 311 nm was investigated at 298 K using thin films of deliquesced NaNO(3)-synthetic sea salt mixtures. Gas phase NO(2), NO, and halogen products were measured as a function of photolysis time using NO(y) chemiluminescence and atmospheric pressure ionization mass spectrometry (API-MS). The production of NO(2) increases with the halide-to-nitrate ratio, and is similar to that for mixtures of NaCl with NaNO(3). Gas phase halogen production also increased with the halide-to-nitrate ratio, consistent with NO(3)(-) photolysis yielding OH which oxidizes halide ions in the film. Yields of gas phase halogens and NO were strongly dependent on the acidity of the solution, while that of NO(2) was not. An additional halogen formation mechanism in the dark involving molecular HNO(3) is proposed that may be important in other systems such as reactions on surfaces. These studies show that the yield of Br(2) relative to NO(2) during photolysis of halide-nitrate mixtures could be as high as 35% under some atmospheric conditions.
硝酸盐和卤化物离子共存于许多环境系统中，包括海盐粒子、北极积雪和碱性干湖。然而，对于卤化物和硝酸盐离子之间可能存在的协同作用知之甚少。在 298 K 下，使用吸湿后的 NaNO3-合成海盐混合物的薄膜，研究了海盐对 311nm 处 NO3-光化学反应的影响。使用 NO(y)化学发光和大气压电离质谱（API-MS），作为光解时间的函数，测量气相 NO2、NO 和卤素产物。随着卤化物与硝酸盐比例的增加，NO2 的生成量增加，与 NaCl 与 NaNO3 的混合物相似。气相卤素生成量也随着卤化物与硝酸盐比例的增加而增加，这与 NO3-光解生成 OH 一致，OH 在薄膜中氧化卤化物离子。气相卤素和 NO 的产率强烈依赖于溶液的酸度，而 NO2 的产率则不然。提出了一种在暗处涉及分子 HNO3 的额外的卤素形成机制，它可能在其他系统（如表面反应）中很重要。这些研究表明，在卤化物-硝酸盐混合物的光解过程中，Br2 相对于 NO2 的产率在某些大气条件下可能高达 35%。
