References

ACP

Atmospheric Chemistry and Physics

ACP

1680-7324

Copernicus GmbH

Göttingen, Germany

10.5194/acp-9-163-2009

Airborne measurement of OH reactivity during INTEX-B

Mao

¹ ¹¹ Ren

¹ ¹² Brune

W. H.

¹ Olson

J. R.

² Crawford

J. H.

² Fried

³ Huey

L. G.

⁴ Cohen

R. C.

⁵ Heikes

⁶ Singh

H. B.

⁷ Blake

D. R.

⁸ Sachse

G. W.

⁹ Diskin

G. S.

⁹ Hall

S. R.

¹⁰ Shetter

R. E.

¹⁰

Department of Meteorology, Pennsylvania State University, University Park, PA, USA

Science Directorate, NASA Langley Research Center, Hampton, VA, USA

Earth Observing Laboratory, National Center for Atmospheric Research, Boulder, CO, USA

School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA

Department of Chemistry and Department of Earth and Planetary Science, University of California Berkeley, Berkeley, CA, USA

Graduate School of Oceanography, University of Rhode Island, Narragansett, RI, USA

NASA Ames Research Center, Moffett Field, CA, USA

Department of Chemistry, University of California, Irvine, CA, USA

Science Directorate, NASA Langley Research Center, Hampton, VA, USA

Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, CO, USA

now at: School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA

now at: Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL, USA

12 01 2009

9 1 163 173

This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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The full text article is available as a PDF file from http://www.atmos-chem-phys.net/9/163/2009/acp-9-163-2009.pdf

The measurement of OH reactivity, the inverse of the OH lifetime, provides a powerful tool to investigate atmospheric photochemistry. A new airborne OH reactivity instrument was designed and deployed for the first time on the NASA DC-8 aircraft during the second phase of Intercontinental Chemical Transport Experiment-B (INTEX-B) campaign, which was focused on the Asian pollution outflow over Pacific Ocean and was based in Hawaii and Alaska. 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)/Δ time was the OH reactivity. The overall absolute uncertainty at the 2σ confidence levels is about 1 s−1 at low altitudes (for decay about 6 s−1), and 0.7 s−1 at high altitudes (for decay about 2 s−1). 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&plusmn0.8 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.

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