In remote locations, atmospheric aerosols are predominately composed of sulfates. However, in some polluted locations, as much as 50% of the aerosol mass can be composed of organic compounds. These organic molecules reduce the surface tension of aqueous droplets in the atmosphere leading to changes in several important atmospheric parameters, including the conditions required for cloud formation, cloud droplet number concentrations, and local precipitation patterns. To assess how much certain individual compounds contribute to changes in surface tension, laboratory measurements are made on a series of dicarboxylic acids, representative of the organic compounds found in the atmosphere. In this experiment, students first measure the surface tension of solutions containing oxalic, succinic, glutaric, and adipic acid to assess how much these can reduce the surface tension of water as a function of organic concentration. Second, using a low-cost, easy-to-build fog collector and a standard rain gauge, the students collect real-world samples and measure their surface tension. Trends in surface tension behavior of the real-world precipitation samples are compared to the solutions of known compounds, and atmospheric implications are discussed.
Supplement
Instructions for students; Directions for constructing a fog collection; Calculations to relate measurements to cloud formation events under atmospheric conditions
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