Atmos. Chem. Phys. Discuss., 8, 14217-14246, 2008
www.atmos-chem-phys-discuss.net/8/14217/2008/
doi:10.5194/acpd-8-14217-2008
© Author(s) 2008. This work is distributed
under the Creative Commons Attribution 3.0 License.
Review Status
This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Airborne measurement of OH reactivity during INTEX-B
J. Mao1,*, X. Ren1,**, W. H. Brune1, J. R. Olson2, J. H. Crawford2, A. Fried3, L. G. Huey4, R. C. Cohen5, B. Heikes6, H. B. Singh7, D. R. Blake8, G. W. Sachse9, G. S. Diskin9, S. R. Hall10, and R. E. Shetter10
1Dept. of Meteorology, Pennsylvania State Univ., University Park, PA, USA
2Science Directorate, NASA Langley Research Center, Hampton, VA, USA
3Earth Observing Laboratory, National Center for Atmos. Research, Boulder, CO, USA
4School of Earth and Atmos. Sciences, Georgia Inst. of Technology, Atlanta, GA, USA
5Dept. of Chemistry and Dept. of Earth and Planet. Sci., Univ. of California Berkeley, CA, USA
6Graduate School of Oceanography, Univ. of Rhode Island, Narragansett, RI, USA
7NASA Ames Research Center, Moffett Field, CA, USA
8Dept. of Chemistry, Univ. of California, Irvine, CA, USA
9Science Directorate, NASA Langley Research Center, Hampton, VA, USA
10Atmos. Chemistry Division, National Center for Atmos. Research, Boulder, CO, USA
*now at: School of Eng. and Applied Sciences, Harvard Univ., Cambridge, MA, USA
**now at: Rosenstiel School of Marine and Atmos. Science, Univ. of Miami, Miami, FL, USA

Abstract. The measurement of OH reactivity, the inverse of the OH lifetime, provides a powerful tool to investigate the atmospheric photochemistry. A new airborne OH reactivity instrument was designed and deployed for the first time on the NASA DC-8 aircraft during Intercontinental Chemical Transport Experiment-B (INTEX-B) campaign. The OH reactivity was measured by adding OH, generated by photolyzing water vapor with 185 nm UV light in a moveable wand, to the flow of ambient air in a flow tube and measuring the OH signal with laser induced fluorescence. As the wand was pulled back away from the OH detector, the OH signal decay was recorded; the slope of −Δln(signal)/Δtime was the OH reactivity. From the median vertical profile obtained in the second phase of INTEX-B, the measured OH reactivity (4.0±1.0 s−1) is higher than the OH reactivity calculated from assuming that OH was in steady state (3.3±0.8 s−1), and even higher than the OH reactivity that was calculated from the total measurements of all OH reactants (1.6±0.4 s−1). Model calculations show that the missing OH reactivity is consistent with the over-predicted OH and under-predicted HCHO in the boundary layer and lower troposphere. The over-predicted OH and under-predicted HCHO suggest that the missing OH sinks are most likely related to some highly reactive VOCs that have HCHO as an oxidation product.

Citation: Mao, J., Ren, X., Brune, W. H., Olson, J. R., Crawford, J. H., Fried, A., Huey, L. G., Cohen, R. C., Heikes, B., Singh, H. B., Blake, D. R., Sachse, G. W., Diskin, G. S., Hall, S. R., and Shetter, R. E.: Airborne measurement of OH reactivity during INTEX-B, Atmos. Chem. Phys. Discuss., 8, 14217-14246, doi:10.5194/acpd-8-14217-2008, 2008.
 
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