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NARSTO Workshop on Innovative Methods for Emission Inventory Development and Evaluation University of Texas, Austin October 14-17, 2003 |
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Top-down Isoprene Emission Inventory For North America Constructed From Satellite Measurements Of Formaldehyde Columns
Jacob, D.J.1, D.S. Abbot1, P.I. Palmer1, R.V. Martin2, K.V. Chance2
1 Division of Engineering and Applied Science, Harvard University
2 Harvard-Smithsonian Astrophysical Observatory
Formaldehyde (HCHO) columns measured from space by solar UV backscatter provide a proxy for local emissions of reactive volatile organic compounds (VOC). During the growing season in North America, the main reactive VOC contributing to the HCHO column is isoprene. We have compiled a 7-year global record (1995-2001) of HCHO column data from the GOME satellite instrument, and we use these data here to construct a top-down inventory of isoprene emissions and to better understand the factors controlling this emission. Regional relationships between HCHO columns and isoprene emissions are obtained from a global tropospheric chemistry model (GEOS-CHEM), which is also used as an intermediary to validate the GOME data with in situ HCHO measurements from surface sites and aircraft. The top-down isoprene emission inventory generated from the GOME data shows general similarities but also some significant differences with current inventories (GEIA, BEIS). Particularly high emissions are found in the Ozarks. The GOME data reveal a seasonal and interannual variability of isoprene emission that is broadly consistent with current algorithms where it is driven by leaf area index (LAI) and temperature. Discrepancies are explored in terms of possible flaws in the emission algorithms. Critical to the progress of our top-down approach for mapping reactive VOC emissions is better laboratory data for the HCHO yields from the oxidation of different VOCs under different atmospheric conditions including at low NOx.