Investigating the meteorological influence on the Glyoxal-to-Formaldehyde Ratio (RGF)

A multitude of different processes (e.g. biogenic, anthropogenic, pyrogenic) couple the Earth’s surface and the atmosphere by releasing a large variety of trace species. These emissions can lead to air quality degradation and climate forcing amongst others. As the full atmospheric state is hard to capture because of the large number of different species, proxies are of particular interest in atmospheric science.

Two important species in atmospheric chemistry are formaldehyde (HCHO) and glyoxal (CHOCHO), both belonging to the family of volatile organic compounds (VOC). Their sources (direct emissions, secondary production from oxidation of other VOC) and their sinks (photolysis, oxidation by the hydroxyl radical) are similar but differ in importance. These marginally different yields of CHOCHO and HCHO in the individual emission processes can be utilized to discriminate between sources. It was proposed to use their ratio (R_GF) as a proxy of the origin of VOC emissions. Multiple publications investigated this hypothesis and resulted in contradictory conclusions for various different conditions.

To gain additional insights into the drivers and limits of the R_GF ratio, MAX-DOAS data from four stations with systematically different conditions (Orléans France, Athens Greece, Incheon South-Korea, ATTO-Tower Brazil) is analysed with the focus on the ratio and meteorological conditions.

We observe a consistent decrease of R_GF with increasing temperature at all four sites. Accounting for the temperature relationship substantially reduces the annual variability of R_GF and removes the influence of relative humidity on R_GF while the diurnal variability of R_GF remains largely unaffected. In contrast, changing shortwave radiation, boundary-layer height, and wind speed impact R_GF only marginally.