PNNL

Abstract

A large fraction of atmospheric particles are composed of hygroscopic salts that are mixed with variety of organic molecules, of which surfactants represent an interesting and potentially important class. Because of the tendency of surfactant molecules to coat the particles' surface, a monolayer has the potential to completely alter the particles' interactions with the rest of the atmosphere. Given the important role that is played by the interaction of particles with the ambient relative humidity it is critical to develop an understanding of the impact surfactants may exert on particle hygroscopic properties. We present an experimental study of the relationship between the concentrations of a soluble surfactant that is internally mixed with two different hygroscopic salts and particle density, shape and water uptake. We show that the observed particle density provides evidence that the density of the surfactant fraction changes with concentration and that once this is properly taken into account the water uptake data can quantitatively be understood.