References

ACP

Atmospheric Chemistry and Physics

ACP

1680-7324

Copernicus GmbH

Göttingen, Germany

10.5194/acp-12-6219-2012

Isoprene emissions in Africa inferred from OMI observations of formaldehyde columns

Marais

E. A.

¹ Jacob

D. J.

¹ ² Kurosu

T. P.

³ ¹⁰ Chance

³ Murphy

J. G.

⁴ Reeves

⁵ Mills

⁵ Casadio

⁶ Millet

D. B.

⁷ Barkley

M. P.

⁸ Paulot

² Mao

⁹

Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA

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

Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA

Department of Chemistry, University of Toronto, Toronto, Canada

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

Instrument Data quality Evaluation and Analysis (IDEAS), Serco Spa Via Sciadonna 24, 00044 Frascati (Roma), Italy

Department of Soil, Water and Climate, University of Minnesota, St. Paul, MN, USA

Space Research Centre, University of Leicester, Leicester, UK

Atmospheric and Oceanic Sciences, Princeton University, Princeton, NJ, USA

now at: Earth Atmosphere Science, Jet Propulsion Laboratory, Pasadena, CA, USA

18 07 2012

12 14 6219 6235

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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We use 2005–2009 satellite observations of formaldehyde (HCHO) columns from the OMI instrument to infer biogenic isoprene emissions at monthly 1 × 1° resolution over the African continent. Our work includes new approaches to remove biomass burning influences using OMI absorbing aerosol optical depth data (to account for transport of fire plumes) and anthropogenic influences using AATSR satellite data for persistent small-flame fires (gas flaring). The resulting biogenic HCHO columns (ΩHCHO) from OMI follow closely the distribution of vegetation patterns in Africa. We infer isoprene emission (EISOP) from the local sensitivity S = ΔΩHCHO / ΔEISOP derived with the GEOS-Chem chemical transport model using two alternate isoprene oxidation mechanisms, and verify the validity of this approach using AMMA aircraft observations over West Africa and a longitudinal transect across central Africa. Displacement error (smearing) is diagnosed by anomalously high values of S and the corresponding data are removed. We find significant sensitivity of S to NOx under low-NOx conditions that we fit to a linear function of tropospheric column NO2. We estimate a 40% error in our inferred isoprene emissions under high-NOx conditions and 40–90% under low-NOx conditions. Our results suggest that isoprene emission from the central African rainforest is much lower than estimated by the state-of-the-science MEGAN inventory.

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