Behavior of N/sub 2/ and nitrogen oxides in nonthermal plasma chemical processing of hazardous air pollutants

Nonthermal plasma chemical behavior of N/sub 2/-O/sub 2/ mixed gases and nitrogen oxides such as N/sub 2/O, NO, and NO/sub 2/ was investigated to obtain baseline information on the generation of active oxygen species and the formation of inorganic byproducts in the nonthermal plasma chemical processing of hazardous air pollutants (HAPs) with a ferroelectric packed-bed reactor. Ozone concentrations were too low, even in air, to oxidatively decompose 300-1000 ppm of HAPs. The O/sub 2/ concentration in N/sub 2/-O/sub 2/ was the determining factor in the formation of all the nitrogen oxides. N/sub 2/O formation was enhanced with increases in O/sub 2/ concentration and in specific energy density, while a threshold value was observed at around 5% of O/sub 2/ concentration in the formation of NO and NO/sub 2/. Rate-suppressing effect by O/sub 2/, detailed byproduct analyses, and thermochemical data suggest that NO/sub x/ decomposes in its reactions with nitrogen atoms derived from N/sub 2/ dissociation, and that the unimolecular N-O cleavage predominantly occurs for N/sub 2/O. The behavior of nitrogen oxides and their precursors was not affected by hydrogen atoms evolved from hydrogen-rich HAPs such as ethylene and benzene. Halogenated HAPs enhanced NO/sub x/ formation and NO/sub 2/ selectivity. Different additive effects of chlorinated and brominated HAPs were observed in the formation of NO/sub x/ and N/sub 2/O, indicating the involvement of different active oxygen species.