Gas-particle partitioning of alcohol vapors on organic aerosols

Single particle levitation using an electrodynamic balance (EDB) has been found to give accurate and direct hygroscopic measurements (gas-particle partitioning of water) for a number of inorganic and organic aerosol systems. In this paper, we extend the use of an EDB to examine the gas-particle partitioning of volatile to semivolatile alcohols, including methanol, n-butanol, n-octanol, and n-decanol, on levitated oleic acid particles. The measured Kp agreed with Pankow's absorptive partitioning model. At high n-butanol vapor concentrations (103 ppm), the uptake of n-butanol reduced the average molecularweight of the oleic acid particle appreciably and hence increased the Kp according to Pankow's equation. Moreover, the hygroscopicity of mixed oleic acid/n-butanol particles was higher than the predictions given by theUNIFACmodel (molecular group contribution method) and the ZSR equation (additive rule), presumably due to molecular interactions between the chemical species in the mixed particles. Despite the high vapor concentrations used, these findings warrant further research onthe partitioning of atmospheric organic vapors (Kp) nearsources and how collectively they affect the hygroscopic properties of organic aerosols. © 2010 American Chemical Society.