Formaldehyde Desorption and Production from Ice Surfaces

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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.