2002 Annual

Wednesday, 16 January 2002: 3:30 PM
OH and HO2 concentrations, production and loss rates at the La Porte site during TexAQS 2000
M. Martinez, Penn State Univ., University Park, PA; and H. Harder, P. DiCarlo, W. H. Brune, S. R. Hall, R. E. Shetter, E. J. Williams, W. Kuster, and B. T. Jobson
Poster PDF (54.3 kB)
OH and HO2 were observed during the TexAQS campaign in Houston in August/September 2000 by laser induced fluorescence. These highly reactive species have a large impact on the atmospheric chemistry, influencing both ozone production and aerosol formation. In addition total OH loss rates in ambient air were measured using a flow tube experiment.

Mean midday mixing ratios for OH were about 7x106 molecules/cm3 and 10 pptv for HO2. The diurnal development of HOx shows strong dependencies on NOx and other trace gases, giving insight into production mechanisms and sinks for OH and HO2 at different times of the day. The results are compared to those obtained in a different urban environment near Nashville in summer 1999.

Further testing of our understanding of the sources and sinks of HOx can be accomplished by comparison of the measured loss rates with the expected production rates. The OH loss rate measurements are also compared with the sum of the products of all measured OH reactants and their reaction rate coefficients with OH.

The measurements indicate that both species were also sometimes present at night. HO2 occasionally reached more than 10 ppt in air with high alkene and ozone concentrations. Possible reasons for the observed nighttime HOx signals are discussed.

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