GLANCE

Prompted by the novel satellite data of glyoxal (CHOCHO) and formaldehyde (HCHO) retrieved by the high resolution spectra of the TROPOMI sounder, GLANCE aims to assess the global budget of their precursors using the MAGRITTEv1.1 global atmospheric chemistry-transport model (CTM) and an inverse adjoint-based framework. Both compounds are formed in the oxidation of non-methane volatile organic compounds (NMVOCs), with isoprene being the most important in terms of global emissions, and they are also emitted directly, in particular, from biomass burning. CHOCHO is produced at high yields from the oxidation of specific anthropogenic compounds, namely acetylene and aromatic NMVOCs. However, the atmospheric budget of glyoxal is, to this day, still poorly understood. Whereas past studies have shown that models can reasonably well reproduce the satellite observations of HCHO, a severe underprediction of CHOCHO from spaceborne observations has been identified, pointing to a large continental CHOCHO source unaccounted for in models. GLANCE will contribute to fill in the current gap in our understanding of the CHOCHO sources worldwide and to improve the current VOC emission inventories. This is particularly important since the currently available inventories bear large uncertainties.

Within GLANCE, we will first update the model to consider the updated recommendations for the reactive uptake coefficients for CHOCHO to aerosol particles and cloud droplets, the recent detailed chemical oxidation mechanism for aromatic hydrocarbons based on the latest laboratory and theoretical results, and a state-of-the-art chemical mechanism for isoprene oxidation. A joint (two-compound) inversion scheme will be designed to handle the simultaneous use of HCHO and CHOCHO columns as top-down constraints. The emissions to be optimized include biogenic isoprene, biomass burning NMVOCs, two classes of anthropogenic NMVOCs (glyoxal precursors and other compounds), and an additional biogenic precursor meant to account for the missing glyoxal source suggested in previous studies. The emissions will be derived on monthly basis from 2018 to 2020. The inversion results will be evaluated against a wide array of in situ observations, as well as FTIR and MAX-DOAS data.

Furthermore, the outcomes of GLANCE will be compared against 3 aircraft campaigns performed by NOAA: the first airborne CHOCHO measurements from the SENEX 2013 research flights over the southeast U.S., the recent FIREX-AQ 2019 aircraft campaign focusing on wildfires in the western U.S., and the AEROMMA mission planned in summer 2023 over U.S. megacities.The main innovative aspects of GLANCE are:

• the use of the improved high resolution retrievals of HCHO and CHOCHO from TROPOMI in a two-compound inversion framework;
• the first top-down estimation of the emissions of anthropogenic CHOCHO precursors from space;
• the strength and distribution of the missing CHOCHO source, its uncertainty, and the identification of potential candidates explaining it;
• the extensive evaluation of the optimization against in situ, ground-based and aircraft data.