Köhler Theory Analysis (KTA)

Introduction

 

The ability of a given aerosol particle to influence cloud properties is a strong function of its size and composition. Atmospheric aerosols are formed of a mixture of inorganic and organic materials which come from both biogenic and anthropogenic sources (Seinfeld and Pandis, 1997). The ability of inorganic compounds to act as CCN is well understood and explained by Köhler theory (e.g., Raymond and Pandis, 2002). On the other hand, organic compounds and their interactions with water vapor can be more complex (Cruz and Pandis, 1997; Corrigan and Novakov, 1999; Raymond and Pandis, 2002; Hartz et al., 2006) due to the large number of organics present in ambient aerosol, each with its own hydrophobicity, molecular weight, density, solubility and surfactant characteristics; it is the presence of inorganic electrolytes that further influences this intricate chemical “soup”. Nevertheless, carbonaceous-aerosol can readily act as CCN (Novakov and Penner, 1993; Cruz and Pandis, 1997); hence understanding when and how long it takes for these particles to transform into drops is a necessary requirement for improving the certainty of climate change predictions.

 

Improvements on aerosol-cloud droplet interactions can be achieved if the cumulative effects of organics on cloud formation can be represented in a simple and realistic way. To do this information such as molar volume (molar mass over density), solubility, surface tension depression, and droplet growth kinetics has to be obtained from laboratory generated and ambient aerosols for later implementation in global climate models.  To aid in the improvements of parameterizations, a new method called Köhler theory analysis (KTA) has been developed to infer the molar volume and solubility of organic components. In order to infer the molar volume and solubility by KTA, measurements of CCN activity, surface tension, and chemical composition, have been coupled with Köhler theory.