AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Cloud Condensation Nuclei Activity of Secondary Organic Aerosol: Kappa Values for a Range of VOCs, Individually and Combined
Josh Custer, William Madry, Dabrina Dutcher, TIMOTHY RAYMOND, Bucknell University
Abstract Number: 397 Working Group: Aerosols, Clouds, and Climate
Abstract The activation of cloud condensation nuclei (CCN) depends on both particle chemistry and initial particle size. Kappa, a hygroscopicity parameter, relates a particle’s dry diameter to its critical supersaturation$^1. In this study, we determined the kappa value for an extensive list of volatile organic compounds (VOCs). The VOCs that were studied were both biogenic and anthropogenic in nature. The VOCs were primarily monoterpenes, although a few sesquiterpenes were also studied. These VOCs were oxidized in a small Teflon smog chamber using ozone to form secondary organic aerosols. The total aerosol number and activated CCN number concentrations were measured. From these measurements an activation diameter (Dp50), the particle size at which half of all particles activate, was calculated using SMCA$^2. These results represent the largest data-set of the Dp50 of pure and mixed aerosols done using one experimental set-up. In addition to measuring the kappa values, it was also observed that activation diameters decrease as the SOA ages. When multiple VOCs were combined in the smog chamber before oxidation, the measured kappa values showed very little variance and settled into a narrow range independent of the initial VOC mixture composition. This result has significant implications for computational models of radiative transfer and cloud formation.
$^1Petters, M. D., and S. M. Kreidenweis. "A single parameter representation of hygroscopic growth and cloud condensation nucleus activity." Atmospheric Chemistry and Physics 7, no. 8 (2007): 1961-1971.
$^2Moore, Richard H., Athanasios Nenes, and Jeessy Medina. "Scanning mobility CCN analysis—A method for fast measurements of size-resolved CCN distributions and activation kinetics." Aerosol Science and Technology 44, no. 10 (2010): 861-871.