Space-Based Constraints on Terrestrial Glyoxal Production

Glyoxal is a volatile organic compound (VOC) in the atmosphere that is a precursor to ozone and secondary organic aerosol, can be a measure of photochemical activity, and is one of a small number of VOCs observable from space. However, the global budget of glyoxal is not well understood, and there has been limited exploration of whether current chemical transport models reproduce satellite observations of this VOC. In this work we take advantage of recent advances in the retrieval of glyoxal from the Ozone Monitoring Instrument along with retrieved formaldehyde and the GEOS-Chem model to constrain global glyoxal sources. Model glyoxal is produced by direct emissions from fires (6.5Tg/year) and secondary chemical production (32.9Tg/year) from biogenic and anthropogenic precursors. The model reproduces the annual average terrestrial spatial variability in formaldehyde and glyoxal reasonably well, with an R-2 of 0.8 and 0.5, respectively. We find that the model representation of biomass burning, C2H2, glyocolaldehyde, and isoprene-dominated glyoxal production is consistent with the observations of glyoxal and formaldehyde, and the ratio of glyoxal to formaldehyde to within similar to 20%. However, the observations suggest that glyoxal production from the high monoterpene-emitting boreal regions is underestimated in the model, with concentrations low by more than a factor of 3. This suggests that the oxidative chemistry of monoterpenes is not well represented in the GEOS-Chem model and that more laboratory work is needed to constrain the impact of monoterpene emissions on atmospheric composition.