Non-Thermal Plasmas (NTP) are one of the promising new methods of air pollution control for low concentration volatile organic compounds operating. They offer several potential advantages such as high destruction efficiencies, rapid response and low energy requirements. The overall aim of the thesis was to investigate the conversion of two exemplar chlorinated volatile organic compounds: methyl chloride (CH3Cl) and chloroform (CHCl3), in two different types of non-thermal atmospheric pressure plasma reactors: a packed-bed reactor and a parallel-plate dielectric barrier plasma reactor. By determining the chemical reaction mechanisms and optimising plasma processing parameters it is hoped that this will lead to a breakthrough in the design of new plasma reactors for industrial applications. For a nitrogen-oxygen plasma in a packed bed reactor the decomposition mechanism of methyl chloride was initiated by free radical collisions and appeared to be similar to that reported for dichloromethane. For chloroform the initial step appears to be electron impact dissociation which is similar for CCl4 decomposition. The buffer gas (nitrogen, oxygen and argon) significantly affects both the decomposition of chlorinated VOCs (CH3Cl) with argon showing better decomposition efficiency and more useful by-products. The reactor configuration has a significant effect on the decomposition of the chlorinated species (CH3Cl) including the decomposition mechanism, efficiency and formation of end products. The DBD reactor showed better by-products but has low energy efficiency. A tunable diode laser absorption spectrometer based on a VCSEL laser diode was developed for measuring oxygen embedded in the micro- and nano-sized pores of various common dielectric materials: 43 nm pore size ZrO2, 115 nm ZrO2, 69 nm Al2O3, 1 nm <MOF. A molecular absorption line of oxygen at around 760 nm was significantly broader compared with free gas and this was accounted for by wall-collision broadening. Additionally there was a large integrated absorbance enhancement for the embedded oxygen gas due to light scattering leading to very long effective absorption path-lengths. Further work will enable the study of embedded gas in the dielectric barriers during plasma operations.