Quantifying nitrite and peroxynitrite formation from the photolysis of nitrate in/on ice

硝酸盐是极地雪中普遍存在的污染物，其在冰芯中的浓度是大气中氮氧化物污染的历史。人们一度认为，雪中的硝酸盐本质上是惰性的，但十年前，格陵兰的研究人员发现，雪中的硝酸盐会被阳光分解，形成氮氧化物和亚硝酸等产物。这些物种从雪中排放到大气中，在那里它们可以显著改变大气的组成和化学成分。例如，来自雪的氮氧化物可以导致大气最低层形成臭氧，而亚硝酸是羟基自由基的重要来源，羟基自由基是决定大气污染物寿命的关键氧化剂。硝酸盐光分解形成亚硝酸盐和过亚硝酸盐两种产物的效率存在很大的不确定性。研究这些产物的形成非常重要，因为它们是极地地区重要大气气体的主要来源。拟议工作的目标是量化冰中/冰上硝酸盐照射下亚硝酸盐和过氧亚硝酸盐的形成，以便更好地限制北极活性氮和氧化剂的预算。研究人员将通过以下方式实现这一目标：(1)测量在冰中硝酸盐照射期间形成亚硝酸盐和过亚硝酸盐的效率；(2)表征雪中普遍存在的有机分子对亚硝酸盐和过亚硝酸盐形成的影响；(3)研究硝酸盐在冰中/冰上不同位置存在时亚硝酸盐和过亚硝酸盐的产量是否发生变化；以及(4)利用所得结果计算北极雪中硝酸盐光解形成亚硝酸盐和过亚硝酸盐的速率。总体而言，这些结果将显著提高对北极积雪中氮氧化物、臭氧和羟基自由基化学的理解，并应有助于澄清硝酸盐反应对上覆大气边界层的影响。这项工作将使用定义明确的实验室冰样、各种分析技术和简单的数值模拟来确定结果对北极积雪和大气中化学物质的影响。两名研究生和几名本科生将通过拟议的研究得到培训和指导。

Nitrate is a ubiquitous contaminant in polar snow whose concentrations in ice cores serve as a history of nitrogen oxide pollution in the atmosphere. It was once thought that nitrate deposited in snow was essentially inert, but a decade ago researchers in Greenland discovered that snow nitrate is broken down by sunlight to form products such as nitrogen oxides and nitrous acid. These species are emitted from the snow into the atmosphere, where they can significantly change atmospheric composition and chemistry. For example, nitrogen oxides from snow can lead to the formation of ozone in the lowest layers of the atmosphere, while nitrous acid is an important source of hydroxyl radical, a key oxidant that determines the lifetimes of atmospheric pollutants. There is significant uncertainty about the efficiency with which nitrate photodecomposition forms two of its products, nitrite and peroxynitrite. Studying the formation of these products is important because they are major sources of important atmospheric gases in polar regions.The goal of the proposed work is to quantify the formation of nitrite and peroxynitrite from illumination of nitrate in/on ice so that the budgets of reactive nitrogen and oxidants in the Arctic can be better constrained. The investigators would accomplish this goal by: (1) Measuring the efficiencies for nitrite and peroxynitrite formation during nitrate illumination in ice; (2) Characterizing the impacts of organic molecules, which are ubiquitous constituents in snow, on nitrite and peroxynitrite formation; (3) Examining whether yields of nitrite and peroxynitrite vary if nitrate is present in different locations in/on the ice; and (4) Using the results to calculate rates of nitrite and peroxynitrite formation from nitrate photolysis in Arctic snow. Overall, these results should significantly improve understanding of the chemistry of nitrogen oxides, ozone, and hydroxyl radical in the Arctic snowpack and should help clarify the impacts of nitrate reactions on the overlying atmospheric boundary layer. The work would be carried out using well­defined laboratory ice samples, a variety of analytical techniques, and simple numerical modeling to determine the impact of the results on the chemistry in the Arctic snowpack and atmosphere. Two graduate students and several undergraduate students will be trained and mentored through the proposed research.