Kappa Values of Organic Aersols

Aerosols, which are suspended liquid or solid particles within a gas, play significant roles in the environment.  Aerosols have direct effects such as impacts on visibility, cloud formation, and even human health.  The role of aerosols on global climate is still being understood. Aerosols also have indirect effects, which are related to the ways in which aerosols interact with and form clouds.  Indirect forcing by aerosols relates to the way in which the particles in the aerosol interact with water.  The interactions of inorganic aerosols with water are relatively well understood unlike the interactions of organic aerosols. If a particle takes on water it can act as a Cloud Condensation Nucleus (CCN) and contribute to cloud formation. This interaction between aerosol particles and water is still one of the biggest sources of uncertainty in global climate models The ability for a particle to collect water is referred to as its hygroscopicity and is represented by a kappa value. Our hypothesis states that aerosols made from the ozonolysis of chemicals from a class of natural organic products, known as monoterpenes, all share a common hygroscopic growth parameter (κ) with a low variability.

The κ parameter is determined through the simultaneous analysis of aerosols generated in a smog chamber by reacting the monoterpene with ozone. The particles are run at various super saturations through a Condensation Nuclei Counter (CCNC) and a Scanning Mobility Particle Sizer (SMPS). The Dp50, or the diameter at which half the particles are CCN active, is calculated by inputting the data from the CCNC and the SMPS into Scanning Mobility Particle Analyzing (SMPA) processing software.

 The goal of this research project was to find κ values for many single and combinations of monoterpenes as well as to look for a trend in κ values, as more parent compounds were present. Several students have worked on this project in the past, collecting many κ values, we began by analyzing all of the past data. Since our technology has since then improved, we found new κ values for all of the monoterpenes we had available to us. From there we proceeded to run two organic compounds together to begin searching for a trend between more compounds and κ values. Continuing to test our hypothesis we then ran three and four compounds. We concluded our hypothesis to be correct, with the as more monoterpenes were present the κ values converged to approximately 0.145.