Satellite Evidence for Glyoxal Depletion in Elevated Fire Plumes

Abstract

AbstractSpace‐borne observations are used to characterize the fate of formaldehyde and glyoxal in wildfire plumes. Their distribution measured by the Tropospheric Monitoring Instrument reveals striking differences between the two compounds near intense fires. In typical situations, the glyoxal‐to‐formaldehyde ratio is highest near the fire (∼0.1) and decreases downwind of the source area due to the larger contribution of pyrogenic emissions to the glyoxal abundance and to the longer lifetime of formaldehyde. However, a pronounced glyoxal depletion is detected above high‐level clouds, not seen for formaldehyde, likely due to processing in pyrocumulonimbus clouds generated by the fires. This depletion suggests glyoxal retention upon droplet freezing and/or its outgassing in hydrated form in the upper troposphere. The absence of a sizable loss of formaldehyde during convection indicates that its hydration in liquid droplets and subsequent outgassing as methanediol represent at most a minor sink of formaldehyde.