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Published December 15, 1997 | Published
Journal Article Open

The photochemistry of acetone in the upper troposphere: A source of odd-hydrogen radicals

Abstract

This paper summarizes measured photodissociation quantum yields for acetone in the 290-320 nm wavelength region for pressures and temperatures characteristic of the upper troposphere. Calculations combine this laboratory data with trace gas concentrations obtained during the NASA and NOAA sponsored Stratospheric Tracers of Atmospheric Transport (STRAT) field campaign, in which measurements of OH, HO_(2), odd-nitrogen, and other compounds were collected over Hawaii, and west of California during fall and winter of 1995/1996. OH and HO_(2) concentrations within 2 to 5 km layers just below the tropopause are ∼50% larger than expected from O_(3), CH_(4), and H_(2)O chemistry alone. Although not measured during STRAT, acetone is inferred from CO measurements and acetone-CO correlations from a previous field study. These inferred acetone levels are a significant source of odd-hydrogen radicals that can explain a large part of the discrepancy in the upper troposphere. For lower altitudes, the inferred acetone makes a negligible contribution to HO_(x) (HO+HO_(2)), but influences NO_(y) partitioning. A major fraction of HO_(x) production by acetone is through CH_(2)O formation, and the HO_(x) discrepancy can also be explained by CH_(2)O levels in the 20 to 50 pptv range, regardless of the source.

Additional Information

© 1997 American Geophysical Union. Manuscript Accepted: 11 November 1997; Manuscript Received: 8 May 1997. This research was supported in part by the Atmospheric Chemistry Project of the Climate and Global Change Program of NOAA, as well as the Upper Atmospheric Research and Atmospheric Effects of Aviation Projects within NASA. We are indebted to the pilots, crew and mission scientists of the STRAT campaign. They include E . Atlas, J. Margitan, M. H. Proffitt, E. Hintsa, T. E. McElroy, J. Wilson, C. R. Webster, R . D. May, R. Herman, and K. R. Chan. Discussions with Ross Salawitch, Lyatt Jaeglé, Daniel Jacobs, Robert Chatfield, Hanwant Singh, and Michael Trainer are also greatly appreciated.

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