Research

Atmospheric aerosols

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This is an image of the ozonolysis of oleic acid on a pendant drop

Ozonolysis of oleic acid on a pendant drop

Atmospheric aerosols significantly influence climate directly by adsorbing or scattering radiation or indirectly by acting as cloud condensation nuclei. The processing of aerosols by atmospheric oxidants chemically changes the surface, directly affecting these properties. There is a recognized need for systematic studies of surface layer reactivity if realistic models are to be developed for climatological research. Different proxies have been described in the literature however, relatively few focus on reactions occurring at the aerosol surface. The majority of spectroscopic studies have focused on the quantitative determination of reaction products as a function of time. As the techniques utilized are not surface specific but rather bulk phase measurements, they enable the overall reaction to be followed, regardless of where the products reside (surface or liquid phase).

We use organic monolayers on either deposited onto solid substrate or spread at the air-water interface as model systems to mimic the surface of atmospheric aerosols. These films are then exposed to an atmospheric oxidant to determine the kinetics of the oxidation reaction and its affect on inherent surface characteristics of the aerosol. We recently reported the use of a pendant drop for real-time monitoring of surface tension changes due to ozone exposure. This provides a simple experimental set-up that can be used for the reaction kinetics of a wide range of gas-phase and surface reactants without the need for a chromophore or label. This approach enabled us to isolate the kinetics of the surface reaction from other ozone uptake processes via a continuous monitoring of the surface activity of the reactant-product mixture Contact angle measurements on films deposited (by Langmuir-Blodgett deposition) onto solid substrate indicate the extent to which the reaction changes the hydrophilicity of the surface which is directly related to its ability to take up water. This is directly related to the ability of an aerosol particle to take up water and act as a cloud condensation nucleus.

This approach utilizes changes in the inherent properties of the surface to monitor the reactive influence of the oxidant. Furthermore, the surface pressure-area isotherms and interfacial rheology are measured prior to, during and after exposure to ozone to evaluate the influence of the chemical reaction on these surface properties. The ease of variation of subphase and atmospheric conditions make this an easy and versatile approach. In addition, the application of this system can be extended beyond ozonolysis to include processing of aerosols by competing atmospheric oxidants as well as surface oxidation of lung surfactant.


 

Concordia University