ENVR 1 |
| In the Earth's atmosphere, rapid oxidation of biogenic and anthropogenic emissions by OH, O3, NO3, etc. produces organic (acids, alcohols) and inorganic (HNO3, H2SO4) hydrophilic compounds which are key ingredients in aerosol formation and subsequent cloud nucleation. Aerosols are ubiquitous in the atmosphere where they strongly influence climate by scattering and absorption of solar and thermal radiation. Results of studies of solar photo-reduction of atmospheric targets will be described. Most common photochemical reactions are initiated through electronic transitions of molecules that occur in the UV spectral region. Visible light is very much more abundant in the solar spectrum but is not in the correct wavelength range to excite molecular electronic transitions and, so, is not generally considered as a driving force in chemistry. Investigations of sunlight-initiated chemical reactions occurring at low energy where reactions proceed in the ground electronic state following the excitation of a vibrational overtone state by visible light will be discussed. The examples presented are H2SO4 and organic acids where excitation of OH vibrational overtones in the near-IR and visible lying near the solar maximum photon output, leads to dehydration or decarboxylation. The result of this chemistry is conversion of highly oxidized atmospheric compounds to reduced, hydrophilic molecules. These do not accommodate water, changing the aerosol nucleation and growth with significant climate effects. Atmospheric consequences of this solar photochemistry such as the formation of the stratospheric CN layer will be presented. |
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Atmospheric Aerosol Processes
8:30 AM-11:45 AM, Sunday, August 19, 2007 Boston Park Plaza -- Stanbro Rm, Oral
Division of Environmental Chemistry |