Formaldehyde Desorption and Production from Ice Surfaces

将进行从冰表面解吸甲醛的实验室研究，以及从冰中各种前体光解吸甲醛的可能性。水/甲醛混合物将在低温槽中通过喷雾冷冻产生小冰晶，甲醛的解吸量将作为温度的函数进行测量。为了进行类似的研究，还将在该池中制备固体冰样。用激光诱导荧光法在气相中检测解吸的甲醛。在额外的光解研究中，冰样将用大气中发现的典型有机酸(如醋酸、草酸和甲烷磺酸)、硝酸根离子以及过氧化氢和溶解铁的混合物来制备。辐射将在灯下进行，使用滤光片将实验限制在与大气相关的波长，并实现粗略的光谱分辨率。在冰原和雪原上方的极地空气中观察到甲醛，浓度高得令人惊讶。人们对其来源知之甚少(可能是运输、吸附到雪/冰上，然后解吸，以及在雪/冰或空气中当地生产)。作为自由基的来源，它在极地对流层化学中非常重要，可能在高海拔卷云粒子中也是如此。许多实地研究报告了甲醛浓度和化学成分；这将是这类物质的第一次实验室研究。这一项目预计将提供详细的信息，以增进我们对大气/冰界面上的重要过程的理解，并将有助于解释痕量物种的冰芯记录，以及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几名年轻的科学家。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.