Physical Chemistry Laboratory Measurements

Atmospheric aerosol particles, particularly in the submicron range, are now known to contain significant amounts of organic carbon. In fact in some areas of the world, such as biomass burning regions, over 80% of the dry aerosol mass during burning season is organic carbon. Many field studies suggest that much of the organic mass found in atmospheric aerosols is often composed of surfactants, resembling humic-like substances formed in soil and water from degradtaion of biological matter. Humic materials are known, from studies in soil science, to form colloids or micelles in aqueous solutions (see below), where each micelle contains a network of organic molecules shown in green. Some aspects of this project will involve collaborations with Gordon Brown in the Department of Geological and Environmental Sciences at Stanford.

Experiments in our lab are aimed at determining how micelle formation in aerosol solutions can affect their chemical, physical, and optical properties. Specifically in our lab we measure the surface tension, refractive index and water vapor pressure phase lines of colloid-forming organic solutions representative of mixtures found in atmospheric aerosols. Such physical variables play important roles in determining how aerosol particles (1) influence radiative transfer through the atmosphere, (2) change the rate and modes of chemical oxidation pathways in air, and (3) modify cloud formation processes.

 

 

Surface Tension: A Kruss Tensiometer is used in our lab to measure the surface tension and density variations of colloid-forming solutions.

 

Refractive Index: A combination of an Abbe refractometer and an Agilent UV-vis spectrophotometer is used in our lab to determine the real and imaginary components of Refractive Index (RI) of colloid-forming solutions, respectively.

 

 

Hygroscopic Growth: Vapor pressure apparatus to determine the water vapor pressure phase lines of colloid-forming solutions.

 

Relevant References

Tabazadeh, A, Organic aggregate formation in aerosols and its impact on the physicochemical properties of atmospheric particles, Atmos. Environ., 39, 5472, 2005.

Aumann, E., and A. Tabazadeh, The rate of organic film formation on aqueous drops, J. Geophys. Res., Submitted.

Jeremy, H., B. Cline, J. Cabrero, E. Aumann, A. Tabazadeh, Adsorption parameters of atmospherically relevant organic species, J. Geophys. Res., Submitted.