| AVS 57th International Symposium & Exhibition | |
| Surface Science | Tuesday Sessions |
| Session SS-TuP |
| Session: | Surface Science Poster Session |
| Presenter: | T.M. McIntire, University of California, Irvine |
| Authors: | T.M. McIntire, University of California, Irvine O. Ryder, University of California, Irvine P. Gassman, Pacific Northwest National Laboratory Z.H. Zhu, Pacific Northwest National Laboratory S. Ghosal, Lawrence Livermore National Laboratory B. Finlayson-Pitts, University of California, Irvine |
| Correspondent: | Click to Email |
Airborne particles have well-documented effects on human health, visibility, and the chemistry of the atmosphere. Particles play a major role in climate change and are a large source of uncertainty in model predictions of global warming. A significant part of this uncertainty is the lack of understanding of the nature of the organic component. This deficiency includes the chemical speciation and the distribution of the organics between the surface and the bulk of liquid particles, as well as changes due to oxidation during transport in the atmosphere.
Self-assembled monolayers (SAMs) represent a well-defined system for elucidating mechanisms of mixed gas-condensed phase reactions and serve as proxies for organic-coated airborne dust particles. Previous studies have shown that ozone reactions of terminal alkene-silane SAMs generates surface-bound acids, aldehydes, and secondary ozonide (SOZ), as well as gaseous products such as CO, CO2, HCHO, and HCOOH. In addition, the surprising formation of large, hydrophobic organic particles was observed by AFM and Auger electron spectroscopy. A particularly noteworthy result of atmospheric interest is that the uptake of water was not increased upon oxidation of these films, despite the formation of polar carbonyl-containing groups, and SOZ. This has important implications for particles in the atmosphere, since it is generally assumed that oxidation converts hydrophobic surfaces to hydrophilic which take up water more readily, thereby affecting visibility and cloud formation.
The goal of this work was to determine the product functional groups and the 3-D structure of particles produced from the ozonolysis of SAMs formed by attachment of 7−octenyltrichlorosilane (C8= SAM) to silica substrates. A combination of analytical techniques such as single particle FTIR, NanoSIMS, and TOF-SIMS were utilized to study the surface composition and morphology after oxidation. Atmospheric implications for the 3-D structure of SOA, SAM reactions and stability in air, ozonolysis of alkenes on surfaces, and the oxidation of alkenes on airborne dust particles will be discussed.