Surface analysis and imaging of the adsorption and chemical reactivity of polycyclic organic matter on environmental particles

The objective of this research was to develop imaging time-of-flight secondary ion mass spectrometry (TOF-SIMS) to characterize ultra-thin organic films on microscopic particles. An initial application is to evaluate the surface chemistry of polycyclic organic matter (POM) on atmospheric particles and its relationship to environmental toxicity. Aspects of technique development that have been investigated include: (1) Adsorption of POM on fine particles using solution monolayer deposition techniques, (2) Assessment of particle substrate effects, including silica gels and combustion particles such as coal flyash, (3) Characterization of various POM species to evaluate variability in secondary ion yields and quantification issues, (4) Correlation of in situ measurements using TOF-SIMS with additional solvent extraction and chromatographic results including HPLC, and (5) Evaluation of POM surface reactivity involving photochemical degradation.; Results using a Ga microbeam ion source coupled to a time-of flight mass spectrometer indicated that 0.1 monolayer coverages of individual POM species can be detected quasimolecular ions from single particles with diameters typically in the 5 {dollar}rmmu m{dollar} range. Primary ion does were {dollar}{lcub}<{rcub}10sp{lcub}13{rcub}{dollar} ions/{dollar}rm cmsp2{dollar} to minimize surface damage during a typical 10 minute spectrum acquisition from an 40 x 40 {dollar}rmmu m{dollar} image field. The more volatile POMs may migrate from the particle surfaces or desorb during TOF-SIMS measurements. Monotonic increase in average {dollar}rm Msp{lcub}+{rcub}{dollar} signals as a function of BaA coverage on flyash (from 0.03 to 3 monolayers) demonstrated the potential for quantitative measurements. Differences in POM adsorption and reactivity also have been established as a function of particle type.; Both photodegradation and oxidation reactions of particle-associated POM have been observed in situ. For example, BaA formed photooxidation products such as benz (a) anthracenedione on silica. TOF-SIMS results as a function of photo-irradation time also allowed quantitative kinetic studies on single particles. Photoproducts are more difficult to detect on the less reactive flyash surfaces.