Atmos. Chem. Phys. Discuss., 12, 7475-7520, 2012
© Author(s) 2012. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Isoprene emissions in Africa inferred from OMI observations of formaldehyde columns
E. A. Marais1, D. J. Jacob1,2, T. P. Kurosu3,*, K. Chance3, J. G. Murphy4, C. Reeves5, G. Mills5, S. Casadio6, D. B. Millet7, M. P. Barkley8, F. Paulot2, and J. Mao9
1Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA
2School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
3Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA
4Department of Chemistry, University of Toronto, Toronto, Canada
5School of Environmental Sciences, University of East Anglia, Norwich, UK
6Instrument Data quality Evaluation and Analysis (IDEAS), Serco Spa Via Sciadonna 24, 00044 Frascati (Roma), Italy
7Department of Soil, Water and Climate, University of Minnesota, St. Paul, MN, USA
8Space Research Centre, University of Leicester, Leicester, UK
9Atmospheric and Oceanic Sciences, Princeton University, Princeton, NJ, USA
*now at: Earth Atmosphere Science, Jet Propulsion Laboratory, Pasadena, CA, USA

Abstract. We use 2005–2009 satellite observations of formaldehyde (HCHO) columns from OMI 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) follow closely the distribution of vegetation patterns in Africa. We infer isoprene emission (EISOP) from the local sensitivity S=ΔΩHCHOEISOP 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 from OMI. We estimate a 40% error in our inferred isoprene emissions under high-NOx conditions and 40–90% under low-NOx conditions. Comparison to the state-of-science MEGAN inventory indicates a large overestimate of central African rainforest emissions in that inventory.

Citation: Marais, E. A., Jacob, D. J., Kurosu, T. P., Chance, K., Murphy, J. G., Reeves, C., Mills, G., Casadio, S., Millet, D. B., Barkley, M. P., Paulot, F., and Mao, J.: Isoprene emissions in Africa inferred from OMI observations of formaldehyde columns, Atmos. Chem. Phys. Discuss., 12, 7475-7520, doi:10.5194/acpd-12-7475-2012, 2012.
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