Formaldehyde Desorption and Production from Ice Surfaces

将对冰表面的甲醛解吸和冰中各种前体可能产生的甲醛进行实验室调查。 将通过在低温池中喷雾冷冻从水/甲醛混合物中产生小冰晶，并且将测量甲醛的解吸作为温度的函数。 还将在该室中制备固体冰样品，用于类似研究。 通过激光诱导荧光在气相中检测解吸的甲醛。 在另外的光解研究中，将用大气中发现的典型有机酸（如乙酸、草酸和甲磺酸）、硝酸根离子以及过氧化氢和溶解铁的混合物来制备冰样品。 辐射将用灯进行，使用滤光片将实验限制在大气相关波长，并实现粗略的光谱分辨率。甲醛已在积雪空气中观察到，在极地冰盖和雪原上的浓度高得令人惊讶。 人们对它的来源了解甚少（可能是迁移、吸附到雪/冰上随后解吸，以及在雪/冰或空气中当地产生）。 作为自由基的来源，它在极地对流层化学中非常重要，也可能在高空卷云粒子中起作用。 许多实地研究报告了甲醛的浓度和化学性质;这将是第一次进行这类实验室研究，预期该项目将提供详细资料，增进我们对大气/冰界面上重要过程的了解，并将有助于解释微量物种的冰芯记录和极地冰上不寻常的化学环境。 该项目将有助于在一个非常跨学科的领域培训若干青年科学家。该项目还将使艾格尼丝·斯科特学院的本科生受益。

Laboratory investigations of formaldehyde desorption from ice surfaces and the possible photoproduction of formaldehyde from various precursors in ice will be conducted. Small ice crystals will be generated from water/formaldehyde mixtures by spray freezing in a cryogenic cell, and the desorption of formaldehyde will be measured as a function of temperature. Solid ice samples will also be prepared in the cell for similar studies. Desorbed formaldehyde will be detected in the gas phase by laser-induced fluorescence. In additional photolysis studies, ice samples will be prepared with typical organic acids found in the atmosphere (such as acetic, oxalic, and methanesulfonic acids); nitrate ions; and mixtures of hydrogen peroxide and dissolved iron. Irradiation will be performed with a lamp, using filters to restrict the experiments to atmospherically relevant wavelengths, and to achieve rough spectral resolution.Formaldehyde has been observed in firn air and in surprisingly high concentrations in the polar regions over ice sheets and snow fields. There is little understanding of its origin (possibilities are transport, adsorption onto snow/ice followed by subsequent desorption, and local production in snow/ice or air). As a source of radicals it is very important in polar tropospheric chemistry and possibly on high altitude cirrus cloud particles as well. Many field studies have reported on formaldehyde concentrations and chemistry; this would be the first laboratory study of its type.This project is expected to provide detailed information that will improve our understanding of important processes on the atmosphere/ice interface, and will also aid in the interpretation of ice core records of trace species, and of the unusual chemical environments over polar ice. The project will contribute to the training of several young scientists in a very interdisciplinary field. The project will also benefit undergraduate students from Agnes Scott College.