Theory, field measurements, and laboratory experiments concerning the cloud condensation nucleus properties of organic and/or insoluble aerosol components

Predicting how the future climate of Earth will change as a result of increasing human emissions is one of the greatest problems facing science today. The earth's climate is the result of a delicate balance between incoming and outgoing radiation. Anthropogenic emissions of aerosol particles into the atmosphere have the potential to affect the earth's climate in significant ways through both direct and indirect effects on the earth's radiative balance. One of the largest uncertainties in aerosol radiative forcing is associated with the relationship between atmospheric aerosols and cloud formation, properties, and lifetime. Clouds form by water condensing on small particles (aerosols) in the air (referred to as cloud condensation nuclei, or CCN), and how the increasing levels of atmospheric particles will affect Earth's clouds and its hydrologic cycle represents one of the key problems in the science of climate. Through theoretical, field, and laboratory investigations, the results presented here reinforce the importance of atmospheric aerosol chemical composition in determining the ability of an aerosol particle to act as a CCN. A study that incorporates surface tension and limited solubility effects, especially of organic compounds, in parameterizations of cloud droplet activation indicate that these chemical effects can rival those of the meteorological environment. An inverse CCN/aerosol closure study of field measurements indicates that assumptions of simple chemistry and mixing state in the interpretation and analysis of field cloud condensation nuclei (CCN) measurements may not necessarily be sufficient and/or realistic, depending heavily on the location of the field study. Properties of organic compounds, such as functional groups, extent of dissociation, and solubility were found to influence the CCN activity of the compounds in laboratory experiments with pure organic aerosols. However, the importance of careful planning of laboratory experiments, in consideration of the properties of the organic compounds, was reinforced and results were carefully interpreted to avoid experimental bias in the conclusions.