Atmospheric Sciences Division Seminar

- Chemical and physical processes occurring at environmental interfaces can have a profound impact on the chemical balance of the atmosphere. I will discuss two examples from my research:

(1) Heterogeneous ice chemistry relevant to polar stratospheric ozone depletion: We have shown that trace amounts of HCl induce formation of a disordered region, or quasi-liquid layer at the ice surface at stratospheric temperatures. We also showed that surface disordering enhances the chlorine activation reaction of HCl with chlorine nitrate (ClONO2), and also enhances acetic acid (CH3COOH) adsorption. These results impact our understanding of the chemistry and physics of ice particles in the atmosphere, explaining the catalytic role that ice particles play in chlorine activation.

(2) Surface active organic films on aqueous aerosols: We have shown that submonolayer films of expanded-state surfactants can significantly suppress the reactive uptake of N2O5 by submicron aqueous aerosols. We used aerosol flow tube reactors with chemical ionization mass spectrometry detection of the gas and particle phases in order to assess the lifetimes of such films when subject to oxidation in the atmosphere. We conclude that for the aerosol compositions studied, oxidation occurs near the gas-aerosol interface and that the 1 e-fold lifetime of unsaturated organics at the aerosol surface is ~10 minutes due to O3 oxidation under atmospheric conditions. Results will also be shown for the OH oxidation of pure and mixed organic-inorganic aerosols containing palmitic acid.

1. McNeill,V. F., Loerting, T., Geiger, F. M., Trout, B. L., and Molina, M. J. Hydrogen chloride-induced surface disordering on ice. Proc. Natl. Acad. Sci. USA 103, 9422-9427 (2006).
2. McNeill,V. F., Patterson, J., Wolfe, G. M., and Thornton, J. A. The effect of varying levels of surfactant on the reactive uptake of N2O5 to aqueous aerosol. Atmos. Chem. Phys. 6, 1635-1644 (2006).
3. McNeill, V. F., Wolfe, G. M., and Thor