HR: 0800h
AN: A51B-0058    [Abstracts]
TI: Distribution of Formaldehyde Over North America: Implications for Satellite Retrievals and Mapping of Precursor Emissions
AU: * Millet, D B
EM: dbm@io.harvard.edu
AF: Harvard University, Department of Earth and Planetary Sciences 29 Oxford St., Cambridge, MA 02138 United States
AU: Jacob, D J
EM: djj@io.harvard.edu
AF: Harvard University, Department of Earth and Planetary Sciences 29 Oxford St., Cambridge, MA 02138 United States
AU: Blake, D R
EM: drblake@uci.edu
AF: U.C. Irvine, Department of Chemistry 570 Rowland Hall, Irvine, CA 92697 United States
AU: Fried, A
EM: fried@ucar.edu
AF: National Center for Atmospheric Research, Earth Observing Laboratory P.O. Box 3000, Boulder, CO 80307 United States
AU: Heikes, B G
EM: bheikes@gso.uri.edu
AF: University of Rhode Island, Graduate School of Oceanography, Narragensett, RI 02882 United States
AU: Singh, H B
EM: Hanwant.B.Singh@nasa.gov
AF: NASA Ames Research Center, MS 245-5, Moffett Field, CA 94035 United States
AB: Measurements of formaldehyde (HCHO) columns from space have the potential to provide important new constraints on surface emission rates of volatile organic compounds (VOCs). Quantitative interpretation requires characterization of errors associated with HCHO column retrievals and the relationship of these columns to VOC emissions. The largest error in the retrieval is in the air mass factor (AMF) used to relate fitted backscattered radiances to actual vertical columns, which is sensitive to the HCHO vertical distribution and to scattering from aerosols and clouds. Here we use 69 aircraft vertical profiles of HCHO and speciated VOCs collected over eastern North America and the North Atlantic during summer 2004 to determine the local relationships between HCHO columns and VOC emissions, calculate AMFs for HCHO retrievals, assess the errors involved in deriving AMFs with a global 3-D model of atmospheric composition (GEOS-Chem), and draw conclusions regarding the mapping of VOC emissions from space. We show that variability in formaldehyde columns over North America is predominantly driven by isoprene emissions, and that HCHO vertical columns measured from space can be reliably used to infer rates and variability of isoprene emission from North America. From vertical profile measurements of formaldehyde and isoprene, we estimate the average HCHO molar yield from isoprene oxidation over the U.S. in summer at 1.6. We find that the use of the modeled air mass factor in satellite retrievals results in an overall uncertainty of 25 percent at the 1 sigma level for a single retrieval scene. Clouds are a major source of error, increasing the uncertainty for an individual retrieval by a factor of two. Over continents, the mean magnitude of the error in retrieved HCHO vertical columns due to clouds is approximately 18 percent (1 sigma) at 40 percent cloud coverage.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
DE: 0322 Constituent sources and sinks
DE: 0365 Troposphere: composition and chemistry
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005