MEASUREMENT OF HYDROPEROXIDES DURING THE TEXAS 2000 AIR QUALITY STUDY.

Hydroperoxides are important atmospheric oxidants. They are responsible for most of the oxidation of aqueous-phase SO{sub 2} to sulfate in the northeastern United States, resulting in the formation of acid precipitation and visibility-reducing sulfate aerosol (Penkett et al., 1979; Lind et al., 1987; Madronich and Calvert, 1990; Tanner and Schorran, 1995). Atmospheric hydrogen peroxide (H{sub 2}O{sub 2} or HP) is produced by the self-reaction of hydroperoxyl radicals (HO{sub 2}); higher organic peroxides are produced by reaction of HO{sub 2} with alkylperoxyl radicals (RO{sub 2}). Peroxyl radicals, along with OH, are chain carriers in the complex photochemical process that produces tropospheric ozone. Thus, concentrations of peroxides and their free radical precursors depend on solar intensity and ambient concentrations of water vapor, ozone, NO{sub x} (NO + NO{sub 2}), and VOCs (volatile organic compounds). Several investigators have demonstrated that HP and hydroxymethyl hydroperoxide (HOCH2 OOH or HMHP) also may be formed when ozone reacts with alkenes in moist air (Becker et al., 1990; Hewitt and Kok, 1991; Gaeb et al., 1995). Peroxides are the expected sink for peroxyl radicals when concentrations of NO are low. Otherwise, these radicals react with NO to form NO{sub 2}. Under high NO{sub x} conditions, NO{sub z} (oxidation products of NO and NO{sub 2}) becomes the principal radical sink. Therefore, formation rates of peroxides relative to NO{sub z} provide information about the history of an air mass and the expected sensitivity of ozone production to reduced emissions (Kleinman et al., 1997; Sillman, 1995; 1997). Through photolysis and reaction with OH, peroxides also act as a radical source; thus, reliable peroxide measurements are necessary for calculating ozone production rates. In this paper, we will summarize peroxide observations at the Williams Tower, and aboard the U.S. Department of Energy G-1 research aircraft in Houston, TX, during August and September 2000. Temporal and geographical distribution of individual peroxides will be discussed, as well as correlations between peroxides and other trace gas measurements