Unique high mass negative ions in the -200 to -400 mass/charge range with repetitive spacings of 12, 14, and 16 units, representative of oligomeric species, have been detected in single ambient submicrometer aerosol particles using real-time single-particle mass spectrometry during the Study of Organic Aerosols field campaign conducted in Riverside, CA (SOAR) in August and November 2005. These oligomer-containing particles represented 33-40% of the total detected particles and contained other indicators of aging including oxidized organic carbon, amine, nitrate, and sulfate ion markers. Overall, the highest mass oligomeric patterns were observed in small acidic 140-200 nm particles in the summer. Also during the summer, increased oligomer intensities were observed when the particles were heated with a thermodenuder. We hypothesize that heat removed semivolatile species, thereby increasing particle acidity, while concentrating the oligomeric precursors and accelerating oligomer formation. Differences in oligomer behavior with respect to particle size and heating can be attributed to seasonal differences in photochemical oxidation, the relative amount of ammonium, and particle acidity.

The use of perfluorinated anionic carboxylic acids (PFCAs) as surfactants is common and widespread. Investigations of PFCAs have shown that their physical properties and toxicological aspects are dependent upon the carbon chain length. The magnitude of these properties is not a linear function of chain length and as yet no explanation of these unique observations has been made. Their environmental dissemination is expected to be nonproportional to the PFCAs chain length. An understanding of the fundamental underlying reason for this novel physical property, chain length trend, would aid further investigators' interpretation of their environmental and toxicological observations. In this study we have utilized 19F NMR techniques, such as, chemical shift, spin−lattice (T 1), and spin−spin (T 2) relaxation phenomena, coupling constants, and variable-temperature NMR to furnish a qualitative explanation of why increasing the carbon chain length causes unexpected intrinsic property changes within this group of chemicals. Results indicate that polyfluorinated chains adopt helical twist geometry unlike their hydrocarbon counterparts which exhibit a zigzag geometry. Variable-temperature 19F NMR showed that chain rigidity within these molecules is also a function of the fluorocarbon chain length. There is a distinct change in geometry and rigidity of the acid chain between 8 and 10 carbon lengths. These unique geometric changes in this class of compound must be considered when assessing their dissemination in the environment, for example, in the case of environmental modeling.

Solid-state nuclear magnetic resonance (NMR) methods are used to follow the thermal degradation of Krytox 1506, a common perfluoropolyether, following adsorption onto the surfaces of gamma-Al2O3 and a model clay (kaolinite). The alumina studies are complemented with thermogravimetric analysis (TGA) to follow the degradation process macroscopically. Molecular-level details are revealed through 19F magic-angle spinning (MAS), 27Al MAS, and 19F --> 27Al cross-polarization MAS (CPMAS) NMR. The CPMAS results show the time-dependent formation of probable VIAl(O6 - nFn) (n = 1, 2, 3) species in which the fluorine atoms are selectively associated with octahedrally coordinated aluminum atoms. For the alumina system, the changes in peak shapes of the CP spectra over time suggest the early formation of catalytically active degradation products, which in turn lead to the formation of additional perfluoropolyether degradation products. Similar to the alumina system, the kaolinite system also displays new resonances in both the 27Al MAS and 19F --> 27Al CPMAS spectra after thermal treatment at 300 degrees C for up to 20 h but reveals a more distinct species at -15.5 ppm that forms at the expense of an initial species (3 ppm), which is in greater abundance at shorter heating times.