The influence of natural and anthropogenic secondary sources on the glyoxal global distribution

International audienceGlyoxal, the smallest dicarbonyl, which has recently been observed from space, is expected to provide indications on VOC oxidation and secondary aerosol formation in the troposphere. Glyoxal is known to be mostly of natural origin and is produced during biogenic VOC oxidation. However, a number of anthropogenically emitted hydrocarbons, like acetylene and aromatics, have been positively identified as glyoxal precursors. The present study investigates the contribution of pollution emissions to the glyoxal levels by taking into account only the secondary chemical formation of glyoxal from precursors emitted from biogenic, anthropogenic and biomass burning sources. For this purpose, a global 3-dimensional chemistry transport model of the troposphere (TM4) able to simulate the gas phase chemistry coupled with all major aerosol components is used. The model results are compared with satellite observations of glyoxal columns over hot spot areas. According to TM4 model results, the anthropogenic contribution to the glyoxal columns is found to reach 70% in the industrialized areas of the northern hemisphere and up to 20% in the tropics. It is on average three times larger than the secondary production of glyoxal from biomass burning sources. The chemical production of glyoxal is calculated to equal about 56 Tg y-1 with 70% produced from biogenic hydrocarbons oxidation, 17% from acetylene, 11% from aromatic chemistry, and 2% from ethene and propene. Glyoxal is destroyed by reactions mainly with OH radicals (22%) and by photolysis (65%), but it is also removed from the atmosphere through wet (11%) and dry deposition (6%). Secondary organic aerosol potential formation through glyoxal losses on/in aerosols and clouds was neglected here due to the significant uncertainties associated with the underlying chemistry. The global annual mean glyoxal burden and lifetime in the model domain are estimated at 0.02 Tg and 3 h, respectively