This page was last modified on January 3, 2005

 

Organic Aerosols

In 1999 Ellison, Tuck and Vaida proposed a model for nascent marine aerosols [J. Geophys. Res., 104, 11633-11643 (1999)]. This model marine aerosols pictures them as inverted micelles.

The model also predicted that the aerosol's organic surfactants would be steadily oxidized by free radicals in the atmosphere. This "processing" by atmospheric radical chemistry transforms the organic film from a hydrophobic substance into a hydrophilic layer. Consequently, the oxidized aerosols are much better cloud condensation nuclei than the nascent particles.

We have built an experiment to survey the oxidation of organic films by OH radicals and O₃ under carefully controlled conditions. We believe that organic films are useful models for marine aerosols. The experiment is one in which we can mount and characterize self-assembled monolayers (SAMs) of simple organic molecules on a gold substrate. This apparatus is housed in a vacuum chamber of roughly 10^-9 Torr and we are able to dose the SAM with an intense beam of OH radicals or ozone. The radicals trigger a cascade of organic free radical chemistry.

We characterize the organic films that are oxidized by the hydroxyl radicals by infrared (IRAS) and ultraviolet (UV) absorption spectroscopy. A residual gas analyzer monitors the extrusion of any small species (such as NO₂ or CO₂) into the gas phase over the SAM. Our most important goal in these experimental studies is to understand the fate of the organic film. As the organic material is oxidized, what are the reaction products? How does the film fragment? What small organic species are released into the gas phase? What is the chemical nature of the resulting film "left behind"? How fast does this chemistry occur?

We have extended this inverted micelle model for organic aerosols into biology [Proc. Natl. Acad. Sci. USA, 97, 11864-11868 (2000)].

 

© 2005 Department of Chemistry and Biochemistry, University of Colorado at Boulder