9730010 Minschwaner This project will extend the twenty-year record of the hydroxyl radical (OH) column abundances from Fritz Peak, CO. The hydroxyl radical is one of the most chemically active constituents in the Earth's atmosphere, playing a direct role in the chemical budget of stratospheric ozone and mediating the transformation between reactive and stable compounds of chlorine and nitrogen. These are ground-based measurements of the resonant absorption of sunlight at 308 nm using a custom designed, high resolution-luminosity product spectrometer. Additional observations will be made using a second instrument located at the New Mexico Institute for Mining and Technology, with emphasis on new instrumentation and analysis procedures. Efforts will be made to improve the signal to noise ratio in auxiliary measurements of OH which involve the Doppler shift in solar limb spectra. A comprehensive analysis will be undertaken of the stray light characteristics of the spectrometers, including comparisons to other instruments, such as the MAHRSI instrument on the Space Shuttle and the FTUV measurements at JPL. Analysis work will be continued through the development of a 1-D version of the NCAR ROSE model and testing of various mesospheric mechanisms. Current photochemical models fail to reproduce the observed geographic, diurnal, seasonal, and secular changes observed in the OH column abundances.
