Formation and composition of organic aerosols from the uptake of glyoxal on natural mineral dust aerosols: a laboratory study

Abstract. The uptake of glyoxal on realistic submicron mineral dust aerosol particles from a natural soil (Gobi Desert) is investigated during experiments in a large simulation chamber, under variable experimental conditions of relative humidity (RH), irradiation, and ozone concentrations. The uptake of glyoxal on the dust particles starts as soon as the glyoxal is injected into the chamber. At 80 % RH, the measured uptake coefficient of glyoxal on mineral dust is γ = (9±5) × 10−3. The totality of the mass of reacting glyoxal is transformed into organic matter on the surface of the dust particles. The uptake of glyoxal is accompanied by the appearance of marker peaks in the organic mass spectra and a persistent growth in the volume concentration of the dust particles. While the mass of the organic matter on the dust rapidly reverts to values prior to uptake, the organic composition of the dust is modified irreversibly. Glycolic and other organic acids, but also oligomers, are detected on the dust. At 80 % RH, compounds ranging from C4 to C10 are observed as oligomerization products of glyoxal mono- and di-hydrate forms. The study suggests that dust aerosols could play a very substantial role in the formation of organic aerosols at high RH, but also that the reaction could have potentially important implications for the dust optical and hygroscopic properties, including their pH.