Revisiting the global budget of atmospheric glyoxal: updates on terrestrial and marine precursor emissions, chemistry, and impacts on atmospheric oxidation capacity

Abstract. Glyoxal (CHOCHO), the smallest dicarbonyl, plays critical yet incompletely understood roles in tropospheric chemistry. Current models substantially underestimate glyoxal abundance over both land and ocean, indicating knowledge gaps in our understanding of its sources and sinks. Here, we present an improved global simulation of atmospheric glyoxal using the GEOS-Chem model, advanced by recent theoretical, experimental, and observational insights on precursor emissions, chemical pathways, and heterogeneous losses. By applying top-down-constrained biogenic emissions, revising glyoxal yields from isoprene, monoterpenes, and glycolaldehyde oxidation, and enhancing biomass burning emissions, we estimated a global atmospheric glyoxal source of 44 Tg yr-1 and a global burden of 15 Gg, substantially reducing the normalized mean bias (NMB) of simulated glyoxal abundance by more than 20 % against in situ and TROPOMI satellite observations over land. The improved representation increases global mean surface ozone by 1.3 ppb (4.8 %) and SOA formation by 5.0 Tg yr-1 (3.8 %). Further inclusion of a hypothetical secondary marine glyoxal source increased the global glyoxal source to 110 Tg yr-1 and the global burden to 39 Gg, substantially improving agreement with in-situ (NMB from -92 % to 12 %) and satellite observations (NMB from -88 % to -6 %) over the ocean. This enhanced glyoxal increased surface HO2 concentrations and OH reactivity over tropical oceans by 6.8 % and 2.3 %. Our work reconciles major model-measurement discrepancies for atmospheric glyoxal, enhancing its utility as a volatile organic compound proxy and underscoring the need for accurate representation of glyoxal sources and chemistry in atmospheric models.