Heterogeneous Reactions of Methacrolein and Methyl Vinyl Ketone on α-Al2O3 Particle

The heterogeneous reactions of methacrolein (MAC) and methyl vinyl ketone (MVK) on alpha-Al2O3 surfaces have been studied in a flow reactor using transmission-Fourier Transform Infrared (T-FTIR) spectroscopy to monitor the reaction progress. Unlike SiO2 particles where MAC and MVK are weakly physisorbed, the results in this work demonstrate that on alpha-Al2O3 particles MAC and MVK are irreversibly adsorbed and can rapidly react on the surface to form various products Such as aldehydes, organic acids, hydrogen peroxide, and even higher molecular weight compounds. The initial uptake rates and initial uptake coefficients for MAC and MVK on alpha-Al2O3 under dry conditions were determined to explore the reactivity of the particles. Furthermore, the effect of water vapor on the heterogeneous reactions was also investigated as a function of relative humidity. Both the heterogeneous uptake and transformation of MAC and MVK on alpha-Al2O3 were largely suppressed under humid conditions due to the depletion of surface active sites by water molecules. On the basis of experimental results, atmospheric implications of heterogeneous reactions of MAC and MVK were discussed. Our work suggests that heterogeneous reactions on alpha-Al2O3 can be important sinks for MAC and MVK as well as possible contributors to atmospheric organic aerosol.