AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
The Composition of Droplet-Forming Aerosol as a Function of Supersaturation
BETH FRIEDMAN, Eleanor Browne, Karin Ardon-Dryer, Anthony Carrasquillo, Kelly Daumit, Kelsey Boulanger, Jesse Kroll, Joel A. Thornton, Daniel Cziczo, University of Washington
Abstract Number: 354 Working Group: Aerosols, Clouds, and Climate
Abstract Aerosol-cloud interactions represent a significant uncertainty with respect to radiative forcing and climate with both particle composition and size playing key, yet poorly understood, roles in determining the cloud nucleating capabilities of aerosols. Cloud condensation nuclei (CCN) and aerosol composition measurements were conducted during February 2013 as part of the Department of Energy Two Column Aerosol Project (TCAP). Located in North Truro, MA, the site provides access to a variety of air mass sources, including marine, continental, and urban.
A CCN closure study was conducted with measurements from a commercial Cloud Condensation Nuclei Counter (CCNC, Droplet Measurement Technologies) at a range of supersaturations, as well as an Aerosol Mass Spectrometer (AMS, Aerodyne). Further measurements were conducted utilizing a Pumped Counterflow Virtual Impactor (PCVI) in order to separate the activated droplets, as a function of supersaturation, from un-activated aerosol at the output of the CCNC. Subsequent composition analysis of the residual droplet aerosol was conducted with the AMS. High-resolution residual aerosol composition will be presented as a function of instrument supersaturation and air mass, and will be compared to the total ambient aerosol composition. Preliminary results suggest an enhancement of nitrate in the activated fraction, as well as compositional differences in organics between the unactivated aerosol and the droplet residuals. The advantages and disadvantages of a combination of a CCN / PCVI / AMS will be discussed with a focus on how this new technique can improve our understanding of warm cloud formation.