Global space-based isoprene measurements constrain emissions and atmospheric oxidation

Isoprene is the dominant non-methane organic compound emitted to the atmosphere1-3, where it drives ozone and aerosol production, modulates atmospheric oxidation, and interacts with the global nitrogen cycle4-8. Isoprene emissions are highly uncertain1,9, as is the non-linear chemistry coupling isoprene and its primary sink (the hydroxyl radical, OH)10-13. Here we present the first global isoprene measurements from space, and show that combined with measurements of its oxidation product formaldehyde, these data provide new constraints on isoprene emissions and atmospheric oxidation. We find that isoprene:formaldehyde relationships measured from space are broadly consistent with current understanding of isoprene-OH chemistry, with no indication of missing OH recycling at low-NOx. We analyze these datasets over four global isoprene hotspots in relation to model predictions, and present a first demonstration of isoprene emission quantification based directly on satellite measurements of isoprene itself. Major discrepancies emerge over Amazonia, where current underestimates of natural NOx emissions bias modeled OH and hence isoprene, and southern Africa, where a prominent isoprene hotspot is missing from bottom-up predictions. A multi-year analysis sheds light on interannual isoprene variability, including the role of El Nino, and demonstrates the potential for the CrIS measurements to further advance understanding of ecosystem processes, isoprene emissions, and atmospheric chemistry.