AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Modification of Droplet Sizes Due to Mixing in Anthropogenic Aerosols
EMMANUEL FOFIE, Diep Vu, Akua Asa-Awuku, University of California, Riverside
Abstract Number: 135 Working Group: Aerosols, Clouds, and Climate
Abstract Cloud droplet size influences the optical depth of clouds and hence particle scattering and the resulting estimates of global cloud radiative forcing. Yet, the sizes of droplets formed from the activation of aerosols either in their pure states, externally or internally mixed is not well characterized. In this study, we explore the effects of organic anthropogenic aerosol such as succinic acid, malonic acid, ammonium sulfate and soot (Black carbon) on cloud droplet sizes. The final droplets sizes are measured from pure and mixed aerosol species. Aerosol activate, form cloud condensation nuclei (CCN) and their droplet growth is characterized according to their mass accommodation coefficient and mixing states. A custom built flowtube was employed to achieve the different mixing states of the aerosol and NIST-certified borosilicate glass beads were used to verify the sizing of the optical particle sizer of the DMT, Inc. cloud condensation nuclei counter (CCNc). A coupled analysis of laboratory CCN experiments and simulation data from the continuous-flow streamwise thermal gradient CCN (CFSTGC) model showed a distinguishable and repeatable divergence in the sizes of CCN when exposed to the same supersaturation and time, with water vapor depletion effects considered. The results suggest that the final droplet sizes of activated aerosol depends on the chemistry of the aerosol represented by the hygroscopicity parameter, κ, as well as the mass accommodation coefficient. The amount of each aerosol species in the atmosphere and their mixing states may therefore have to be considered when computing the earth’s radiative forcing.