UC Riverside

This thesis mainly focuses on (1) development and applications of cavity ringdown spectroscopy (CRDS) to study atmospheric trace gases; (2) reactive intermediates in the alkene ozonolysis reactions using photoionization time-of-flight mass spectrometry (TOFMS); and (3) development of new methods using CRDS for thin film studies.

Specifically, CRDS based instruments are developed to measure and characterize peroxy radicals in atmosphere. By combining the chemical amplification detection of peroxy radicals (PERCA) with CRDS, the peroxy radical detection sensitivity can achieve ~10pptv/60s with a single channel CRDS instrument and ~1.2pptv/10s with a dual channel CRDS instrument. Ambient measurements of the peroxy radicals were carried out. The same dual channel instrument is also used for measurements of optical

extinction of atmospheric aerosols, which is in good agreement with the Mie theory with a sensitivity of 0.24 Mm-1(1σ).

To detect the early transient reactive intermediates and investigate the mechanisms of initial steps of ozonolysis of alkenes, the gas-phase ozonolysis reactions are carried out in a fast flow reactor under the conditions of low pressure (7-10 Torr) and room temperature. The alkenes investigated include cis-2-butene, tetramethylethylene, cyclohexene, isoprene and - and -pinenes. CO is used as an OH scavenger to minimize the reactions between the OH byproduct and alkenes. After a short reaction time of ~25 to ~ 200 μs, the initial products, both free radical intermediates and stable species, are detected by the 118-nm vacuum ultraviolet (VUV) photoionization TOFMS. Mass peaks corresponding to the Criegee intermediates or their isomers are identified.

This thesis also presents a novel method for determining the thickness of a non-absorbing nanoscale thin film on a nearly transparent substrate through the analysis of the transmittance signal measured using CRDS near the Brewster angle. An optical model is developed and demonstrated for a organic polymer thin film.

This dissertation is a part of my research work. For environmental chamber study of atmospheric chemistry and secondary organic aerosol formation using cavity enhanced absorption spectroscopy please refer to my MS degree thesis in Chemistry and Environmental Engineering department, UC-Riverside.