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HO_x chemistry during INTEX-A 2004: Observation, model calculation, and comparison with previous studies

Ren, Xinrong and Olson, Jennifer R. and Crawford, James H. and Brune, William H. and Mao, Jingqiu and Long, Robert B. and Chen, Zhong and Chen, Gao and Avery, Melody A. and Sachse, Glen W. and Barrick, John D. and Diskin, Glenn S. and Huey, L. Greg and Fried, Alan and Cohen, Ronald C. and Heikes, Brian and Wennberg, P. O. and Singh, Hanwant B. and Blake, Donald R. and Shetter, Richard E. (2008) HO_x chemistry during INTEX-A 2004: Observation, model calculation, and comparison with previous studies. Journal of Geophysical Research D, 113 (D5). Art. No. D05310. ISSN 0148-0227. doi:10.1029/2007JD009166.

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OH and HO_2 were measured with the Airborne Tropospheric Hydrogen Oxides Sensor (ATHOS) as part of a large measurement suite from the NASA DC-8 aircraft during the Intercontinental Chemical Transport Experiment-A (INTEX-A). This mission, which was conducted mainly over North America and the western Atlantic Ocean in summer 2004, was an excellent test of atmospheric oxidation chemistry. The HOx results from INTEX-A are compared to those from previous campaigns and to results for other related measurements from INTEX-A. Throughout the troposphere, observed OH was generally 0.95 of modeled OH; below 8 km, observed HO_2 was generally 1.20 of modeled HO_2. This observed-to-modeled comparison is similar to that for TRACE-P, another midlatitude study for which the median observed-to-modeled ratio was 1.08 for OH and 1.34 for HO_2, and to that for PEM-TB, a tropical study for which the median observed-to-modeled ratio was 1.17 for OH and 0.97 for HO_2. HO_2 behavior above 8 km was markedly different. The observed-to-modeled HO_2 ratio increased from ∼1.2 at 8 km to ∼3 at 11 km with the observed-to-modeled ratio correlating with NO. Above 8 km, the observed-to-modeled HO_2 and observed NO were both considerably greater than observations from previous campaigns. In addition, the observed-to-modeled HO_2/OH, which is sensitive to cycling reactions between OH and HO_2, increased from ∼1.5 at 8 km to almost 3.5 at 11 km. These discrepancies suggest a large unknown HO_x source and additional reactants that cycle HO_x from OH to HO_2. In the continental planetary boundary layer, the observed-to-modeled OH ratio increased from 1 when isoprene was less than 0.1 ppbv to over 4 when isoprene was greater than 2 ppbv, suggesting that forests throughout the United States are emitting unknown HO_x sources. Progress in resolving these discrepancies requires a focused research activity devoted to further examination of possible unknown OH sinks and HO_x sources.

Item Type:Article
Related URLs:
URLURL TypeDescription ItemSupporting Information
Brune, William H.0000-0002-1609-4051
Diskin, Glenn S.0000-0002-3617-0269
Huey, L. Greg0000-0002-0518-7690
Cohen, Ronald C.0000-0001-6617-7691
Wennberg, P. O.0000-0002-6126-3854
Alternate Title:HOx chemistry during INTEX-A 2004: Observation, model calculation, and comparison with previous studies
Additional Information:© 2008 American Geophysical Union. Received 13 July 2007; revised 24 October 2007; accepted 18 December 2007; article first published online 8 March 2008. The work was supported by the NASA Tropospheric Chemistry Program. The authors would like to thank the DC-8 crew and support staff during the INTEX-A preparation and deployment periods for making this work possible. Please note: Wiley Blackwell is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.
Group:UNSPECIFIED, Division of Geological and Planetary Sciences
Funding AgencyGrant Number
Subject Keywords:hydroxyl radical; hydroperoxyl radical
Issue or Number:D5
Record Number:CaltechAUTHORS:20140702-102532813
Persistent URL:
Official Citation:Ren, X., et al. (2008), HOx chemistry during INTEX-A 2004: Observation, model calculation, and comparison with previous studies, J. Geophys. Res., 113, D05310, doi:10.1029/2007JD009166.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:46633
Deposited By: Ruth Sustaita
Deposited On:02 Jul 2014 20:12
Last Modified:10 Nov 2021 17:28

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