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

Atmospheric glyoxal (CHOCHO) 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 isoprene emissions, enhancing biomass burning emissions, and revising glyoxal yields from isoprene, monoterpenes, and glycolaldehyde oxidation, we estimated a global atmospheric glyoxal source of 40 Tg yr⁻¹ and a global burden of 15 Gg, substantially reducing low bias of simulated glyoxal abundance against in situ and TROPOMI satellite observations over land. The improved representation of glyoxal and its precursors increases simulated global mean surface ozone by 4.5 ppb (17 %) and SOA formation by 17.9 Tg yr⁻¹ (13 %), indicating stronger atmospheric oxidation capacity. Further inclusion of a hypothetical secondary marine glyoxal production to match TROPOMI glyoxal observations over the global oceans increased the global source of atmospheric glyoxal to 106 Tg yr⁻¹ and its global burden to 39 Gg, substantially improving agreement with in situ (NMB from -92 % to 12 %) over the ocean. This enhanced marine glyoxal source increased surface HO₂ concentrations and OH reactivity over tropical oceans by 6.5 % and 1.9 %. However, this hypothetical marine glyoxal source cannot be accounted for by known marine NMVOC emissions; its existence remains highly uncertain and warrants further investigation. Our work helps reconcile major model-measurement discrepancies for atmospheric glyoxal, enhances its utility as a volatile organic compound (VOC) proxy, and underscores the need to further investigate glyoxal sources and chemistry.