March 2008: Spatial distribution of isoprene emissions from North America derived from formaldehyde column measurements by the OMI satellite sensor
We use space-borne formaldehyde (HCHO) column measurements from the Ozone Monitoring Instrument (OMI), with 13 x 24 km2 nadir footprint and daily global coverage, to develop new constraints on the spatial distribution of biogenic isoprene emission from North America.
The above plot shows mean OMI HCHO columns for June-August 2006. The spatial distribution of OMI HCHO columns follows that of isoprene emission; anthropogenic hydrocarbon emissions are undetectable except in Houston. We compare the OMI-derived emissions to a state-of-science bottom-up isoprene emission inventory (MEGAN) driven by two land cover databases, and use the results to optimize the MEGAN emission factors (EFs) for broadleaf trees (the main isoprene source). The OMI-derived isoprene emissions in North America are spatially consistent with MEGAN but are lower (by 4-25% on average). MEGAN overestimates emissions in the Ozarks and the Upper South. A better fit to OMI is obtained in MEGAN by using a uniform isoprene EF from broadleaf trees rather than variable EFs. Thus MEGAN may overestimate emissions in areas where it specifies particularly high EFs. For more details see Millet et al. [2008].