Effect of Surfactants on Cloud Condensation Nuclei

Aerosols are present everywhere. They are formed simply by diffusion of particles into the air from surfaces of materials all around us. Inevitably, these particles will end up in the atmosphere, and many of these particles will end up acting as Cloud Condensation Nuclei (CCN). A CCN particle forms a surface on which water molecules accumulate. These CCN particles might be very small but can hold a very large amount of water. In the atmosphere, these particles are of great importance, because as the name might suggest, clouds form because of them. An ability to manipulate the uptake of water by these particles might be of great value in relatively new ideas like cloud seeding (manipulating precipitation) or global climate modeling, which could help us understand more about climate sensitivity.

This research project was conducted during the years 2015-2016 to investigate the effect of surfactants on the uptake of water by dry aerosols. For this purpose, a dilute solution of a solvent (typically 1 gram per liter) in deionized water was taken in a syringe that was connected to a device allowing a constant flow of the given solution. It would then be turned into an aerosol by the â??atomizerâ?, a device that blasts the very small stream of the given solution with a large amount of air. Then the resultant aerosol flowed through a series of dryers that removed all the water. The final product was passed through a particle counter and a Cloud Condensation Nuclei Counter (CCNC). The particle counter would count the number of particles flowing through the tubes and the CCNC acted to pass the aerosol through a supersaturated humid environment and to measure the number of particles that would take up water and grow in size, and the size of those particles.

The idea behind this project was to see whether the uptake of water by the particles could be manipulated by adding surfactants. Surfactants (short for surface-active agents) are substances that affect the surface tension of water (or any solvent that they are dissolved in). A decrease in surface tension was theorized to be a factor in the amount of water that could accumulate around a particle, and various surfactants were tested throughout the course of the research project to see their effects on the growth of particles.