AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Comparison of n-Alkanoic Acid Surface Pressure Isotherms Determined for Microscopic Droplets and Macroscopic Solutions
CHRIS RUEHL, Kevin Wilson, Athanasios Nenes, Patrick Chuang, Allen H. Goldstein, Univeristy of California, Berkeley
Abstract Number: 528 Working Group: Aerosols, Clouds, and Climate
Abstract Ambient organic aerosols can reduce the surface tension of macroscopic aqueous solutions, and often parameterizations based on these measurements are used to predict cloud condensation nuclei (CCN) activity for microscopic droplets. However, it is not known to what extent these parameterizations may need to be altered in response to the much higher surface:volume ratios of such droplets. Here we determine the surface tension of 1-2 micro-meter droplets formed at RH=99.9% from particles containing one of a series of n-alkanoic acids and NaCl. By varying the acid:NaCl ratio of the particles, we relate the reduction in surface tension to the maximum thickness of the organic film on the wet droplet. We compare the microscopic parameterization that we generate to previously-published macroscopic surface pressure vs. surface concentration relationships for the same compounds. The results provide a specific test to determine if macroscopic surface tension parameterizations are valid for microscopic droplets. We also discuss the general differences in droplet surface tension obtained with a bulk parameterization (e.g., the Szyskowski equation) and a surface parameterization, and show that the latter is preferable for calculating CCN activity.