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Quantitative estimates of emissions of ozone precursors, in particular nitrogen oxides (NOx=NO+NO2) and volatile organic compounds (VOCs), remain highly uncertain. Space-based observations of NO2 and HCHO from the Global Ozone Monitoring Experiment (GOME) can provide a new perspective on these emissions. GOME has provided global measurements since 1995 onboard the European Remote Sensing-2 (ER-2) satellite. We are using the GEOS-CHEM 3-D model of tropospheric chemistry to retrieve the GOME vertical tropospheric columns of NO2 and HCHO. The model is also used to relate NO2 and HCHO columns to surface emissions of NOx and VOCs in inverse modeling studies. |
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Initially, we focused our analysis on Africa, where large-scale fires spread each year during the dry season. Rains in the early spring bring much-needed water and put an end to the fires. Rains also activate dormant soil bacteria, which begin to use nitrogen, thus releasing a pulse of nitric oxide into the atmosphere. We used satellite observations of NO2 columns from GOME to map the extent of this biological pulse, which spreads over 3 million km2 of the Sahel. We found that soil emissions (40% of African emissions) rival in magnitude emissions from fires and can thus have a large influence on ozone enhancements over and downwind of Africa [Jaeglé et al., 2004, see publications below]. |
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We then expanded our study to examine the global partitioning of surface NOx sources among fuel combustion, biomass burning and soil emissions. The spatial and seasonal distribution of each of these NOx sources can be clearly mapped from space. By using added information from satellite observations of fires and from the location of fossil fuel dominated regions, we designed a simple method for quantifying each of these sources individually and derived an optimized NOx emission inventory [Jaeglé et al., 2005]. Our resulting global fuel combustion (25.6 TgN) and biomass burning (5.8 TgN/yr) emissions are very close to expected values, and inclusion of GOME observations has helped reduce uncertainties. However, soil emissions are 68% larger than expected, with annual emissions of 8.9 TgN/yr. These microbial soil emissions are particularily large over tropical savanna/woodland ecosystems during the wet season, as well as over agricultural regions in mid-latitudes during summer. These results were presented at the Faraday Discussion in Atmospheric Chemistry. Read the press release. |
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People:
Lyatt Jaeglé, assistant professor (jaegle@atmos.washington.edu)
Linda Steinberger, graduate student (graduated in 2004 with a
M.S.)
Our collaborators in this work are: Randall Martin, Dalhousie University; Kelly Chance, Harvard-Smithsonian Center for Astrophysics; Paul Palmer and Daniel Jacob, Harvard University; Peter Hobbs and Ricky Sinha, University of Washington.
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Jaeglé, L., L. Steinberger, R. V. Martin, and K. Chance, Global partitioning of NOx sources using satellite observations: Relative roles of fossil fuel combustion, biomass burning and soil emissions, Faraday Discussions, in press, 2005. [PDF]
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Jaeglé, L., R. V. Martin, K. Chance, L. Steinberger, T. P. Kurosu, D. J. Jacob, A.I. Modi, V. Yoboué, L. Sigha-Nkamdjou, and C. Galy-Lacaux, Satellite mapping of rain-induced nitric oxide emissions from soils, J.Geophys. Res., 109 (D21310), doi:10.1029/2004JD004787, 2004. [PDF]
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Steinberger, L., "Using space based observations of NO2 and HCHO to map biomass burning emissions of NOx and VOCs over Africa", M.S. Thesis, University of Washington, Seattle, 2004.
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Sinha, P., L. Jaeglé, P.V. Hobbs, and Q. Liang, Transport of biomass burning emissions from southern Africa, J. Geophys. Res., 109, D20204, doi:10.1029/2004JD005044, 2004. [PDF]
Funding:
NASA, New Investigator Program in Earth Science (NAG5-10637), 2001-2004 (PI: Lyatt Jaeglé).