References

ACP

Atmospheric Chemistry and Physics

ACP

1680-7324

Copernicus GmbH

Göttingen, Germany

10.5194/acp-10-9415-2010

HOx observations over West Africa during AMMA: impact of isoprene and NOx

Stone

¹ ² Evans

M. J.

¹ Commane

² ⁹ Ingham

² ³ Floquet

C. F. A.

² ¹⁰ McQuaid

J. B.

¹ Brookes

D. M.

⁴ Monks

P. S.

⁴ Purvis

⁵ ⁶ Hamilton

J. F.

⁶ Hopkins

⁶ ⁷ Lee

⁶ ⁷ Lewis

A. C.

⁶ ⁷ Stewart

⁸ Murphy

J. G.

⁸ ¹¹ Mills

⁸ Oram

⁸ Reeves

C. E.

⁸ Heard

D. E.

² ³

School of Earth and Environment, University of Leeds, Leeds, UK

School of Chemistry, University of Leeds, Leeds, UK

National Centre for Atmospheric Science, University of Leeds, Leeds, UK

Department of Chemistry, University of Leicester, Leicester, UK

Facility for Airborne Atmospheric Measurement, Cranfield University, Cranfield, UK

Department of Chemistry, University of York, York, UK

National Centre for Atmospheric Science, University of York, York, UK

School of Environmental Sciences, University of East Anglia, Norwich, UK

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

now at: National Oceanography Centre, University of Southampton, Southampton, UK

now at: Department of Chemistry, University of Toronto, Toronto, Canada

06 10 2010

10 19 9415 9429

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.

This article is available from http://www.atmos-chem-phys.net/10/9415/2010/acp-10-9415-2010.html

The full text article is available as a PDF file from http://www.atmos-chem-phys.net/10/9415/2010/acp-10-9415-2010.pdf

Aircraft OH and HO2 measurements made over West Africa during the AMMA field campaign in summer 2006 have been investigated using a box model constrained to observations of long-lived species and physical parameters. "Good" agreement was found for HO2 (modelled to observed gradient of 1.23 ± 0.11). However, the model significantly overpredicts OH concentrations. The reasons for this are not clear, but may reflect instrumental instabilities affecting the OH measurements. Within the model, HOx concentrations in West Africa are controlled by relatively simple photochemistry, with production dominated by ozone photolysis and reaction of O(1D) with water vapour, and loss processes dominated by HO2 + HO2 and HO2 + RO2. Isoprene chemistry was found to influence forested regions. In contrast to several recent field studies in very low NOx and high isoprene environments, we do not observe any dependence of model success for HO2 on isoprene and attribute this to efficient recycling of HOx through RO2 + NO reactions under the moderate NOx concentrations (5–300 ppt NO in the boundary layer, median 76 ppt) encountered during AMMA. This suggests that some of the problems with understanding the impact of isoprene on atmospheric composition may be limited to the extreme low range of NOx concentrations.

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