The photodegradation of vanillin, as a proxy of methoxyphenols emitted by biomass burning, was investigated in artificial snow at 243 K and in liquid water at room temperature. Nitrite (NO₂^–) was used as a photosensitizer of reactive oxygen and nitrogen species under UVA light, because of its key photochemical role in snowpacks and atmospheric ice/waters. In snow and in the absence of NO₂^–, slow direct photolysis of vanillin was observed due to back-reactions taking place in the quasi-liquid layer at the ice-grain surface. The addition of NO₂^– made the photodegradation of vanillin faster, because of the important contribution of photoproduced reactive nitrogen species in vanillin phototransformation. These species triggered both nitration and oligomerization of vanillin in irradiated snow, as the identified vanillin by-products showed. Conversely, in liquid water, direct photolysis was the main photodegradation pathway of vanillin, even in the presence of NO₂^–, which had negligible effects on vanillin photodegradation. The results outline the different role of iced and liquid water in the photochemical fate of vanillin in different environmental compartments.

中文翻译：

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亚硝酸盐介导的直接光解作用对人造雪中香兰素的光转化

香草醛作为生物质燃烧排放的甲氧基酚的代表，在 243 K 的人造雪和室温液态水中进行了光降解研究。亚硝酸盐 (NO ₂ ^– ) 因其在积雪和大气冰/水中的关键光化学作用而被用作 UVA 光下活性氧和氮物种的光敏剂。_{在雪中且没有NO 2} ^–的情况下，由于冰粒表面的准液体层中发生逆反应，观察到香草醛的缓慢直接光解。添加 NO ₂ ^–由于光产生的活性氮在香草醛光转化中的重要贡献，使得香草醛的光降解速度更快。正如已鉴定的香草醛副产物所示，这些物种在受辐射的雪中引发了香草醛的硝化和低聚。_{相反，在液态水中，直接光解是香兰素的主要光降解途径，即使有NO 2} ^-存在，对香兰素光降解的影响可以忽略不计。结果概述了冰水和液态水在不同环境分区中香草醛光化学命运中的不同作用。