Observational constraints on water vapor sensitivity of glyoxal to formaldehyde ratio (RGF)

Glyoxal (CHOCHO) to formaldehyde (HCHO) ratio (R_{GF =} [CHOCHO]/[HCHO])) has been suggested as a useful tool to diagnose the origin of air mases, due to their different dependence on precursor volatile organic compounds (VOCs) and NOx (NOx = NO + NO₂) abundance, in their oxidational production processes. Considering the possibility of measurements from satellite for both species, this indicator likely has a significance on a regional and global scale understanding of atmospheric chemical processes, once we have enough of knowledge on the main driver in R_GF factor.

However, the discrepancies on the tendency and absolute magnitude of R_GF among satellite-base and ground/aircraft-based observations limit the uses of this ratio. Extensive efforts have been taken to add more constraints to reconcile these differences, in recent, mainly focused on deepening the knowledge on production of CHOCHO and HCHO aspects.

In this study, we focused on understanding the R_GF from the loss mechanisms by testing the water vapor sensitivity primarily based on the KORUS-AQ 2016 (KORea and U.S.- Air Quality study, 2016) aircraft observations. Spatiotemporal distribution analysis in conjunction with 0-D box modeling work to capture the emission and meteorological impact on R_GF was conducted. As a result, the aromatic VOCs (e.g., toluene, benzene, etc.) are dominating sources of CHOCHO, and the R_GF ranges from 0.02 to 0.09 over Korea. We also found significant decrease in R_GF at higher water vapor mixing ratio (H₂O > 8000 ppmv), and these results are compared with those of other missions in the U.S. (e.g. CalNEX, SENEX, etc.). Our work highlights the implication of water mediated R_GF which may alter the original signature of precursor characteristics.