Abstract

Satellite observations of formaldehyde (HCHO) columns provide additional top-down constraints on isoprene emissions and are especially useful in assessing isoprene emissions from remote and largely inaccessible tropical ecosystems. I will present results from two studies: (a) an analysis of top-down Amazonian isoprene emissions, inferred from GOME HCHO columns observations using the GEOS -Chem chemistry transport model and the MEGAN (Model of Emissions of Gases and Aerosols from Nature) bottom-up inventory, and (b) an empirical orthogonal function analysis on 12 years of global GOME and SCIAMACHY HCHO column observations.

I will show that in most regions, HCHO variability is predominantly driven by seasonal variations of biogenic emissions and biomass burning. However, unusually low HCHO columns are consistently observed over western Amazonia, during the transition from the wet-to-dry seasons. Seasonal variations in MODIS Leaf Area Index (LAI) and Enhanced Vegetation Index (EVI) data are remarkably consistent (correlations of 0.69 and 0.67, respectively) with the observed decrease in HCHO during the wet-to-dry period. Based on this evidence, it is possible isoprene emitters experience widespread leaf flushing prior to the dry season, resulting in a large-scale annual shutdown of Amazonian isoprene emissions.

In addition to these studies, I will show preliminary model and data comparisons to assess the accuracy of a newly developed GEOS -Chem (high-resolution) nested grid Amazon simulation.