The role of coagulation in the growth of aerosol particles at a remote site in Alabama

The concentration of droplets in a cloud influences important properties such as its reflectivity and precipitation efficiency. Cloud droplet concentration is controlled by environmental factors such as base temperature and updraft velocity, and by the concentration of those aerosol particles large and soluble enough to act as cloud condensation nuclei (CCN). Recently nucleated particles must grow by an order of magnitude or more through condensation of inorganic and organic gases to become CCN. I worked with graduate students during a field project in Alabama to measure the size of small-suspended particles trapped in Teflon chambers to understand how rapidly they grow into CCN. To determine the types and concentrations of condensable gases, we first have to correct for growth due to coagulation, which is simply when two particles collide to form a larger one. I wrote a computer program that calculates the coagulation rate of particles in the chamber based on the measured size distribution of the particles that were injected at the beginning of an experiment. The program was used to estimate the change in the size distribution due only to coagulation, which will then be subtracted from the measured overall change to determine the contribution of condensation.