Satellite-based constraints on seasonal methanol emissions from terrestrial landscapes

Methanol (CH₃OH) is the most abundant non-methane volatile organic compound in the atmosphere, with a global burden of 3-4 Tg, and is an important precursor of carbon monoxide, formaldehyde, and ozone. Here we employ an ensemble of new methanol measurements from nadir-viewing space-based sensors (TES, IASI) to better understand seasonal methanol emissions from terrestrial ecosystems worldwide. Analyzing one full year of satellite data, we find that the GEOS-Chem model, driven with MEGANv2.1 biogenic emissions, underestimates observed methanol concentrations throughout the midlatitudes in springtime, with the timing of the seasonal peak in model emissions 1-2 months too late. We attribute this discrepancy to an underestimate of emissions from new leaves in MEGAN, and apply the satellite data to better quantify the seasonal change in methanol emissions for midlatitude ecosystems. Our results enable a more realistic simulation of atmospheric methanol on the basis of IASI, TES, and ground-based measurements. We further employ the adjoint of GEOS-Chem in an inverse analysis to evaluate what constraints the satellite data can provide on methanol emission rates from different plant functional types.