Annual average OMI-derived (left) and MEGAN isoprene emissions (middle) and the difference between the two estimates (right). We show that satellite-based observatons of formaldehyde (HCHO), a high-yield product of isoprene, can be used to estimate isoprene emissions in Africa - a region with limited ground-based observations. In our approach we (1) filter for biomass burning and anthropogenic HCHO sources; (2) remove dusty scenes in north Africa that impact the air mass factor estimate to convert slant columns to vertical columns; (3) account for smearing of the HCHO signal in central Africa where OH levels are low and isoprene emissions are high; and (4) use GEOS-Chem to obtain a NOx-dependent HCHO yield to estimate isoprene emissions. On comparing our top-down isoprene emissions we find that total emissions from the state-of-the-science emission inventory MEGAN are similar to our estimate, but with large spatial discrepancies (see figure above).

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