In situ detection of hazardous waste

Abstract

Chlorinated hydrocarbon (CHC) concentrations have been successfully measured in situ in nonreactinggas mixtures and in flames. These measurements were made by fragmenting the CHCs with a 193-nm excimer laser and detecting the CCl fragment with a second laser via laser-induced fluorescence. Since fragmentation produces vibrationally excited CCl molecules, we can efficiently detect them by exciting the 1→0 band of the X2II→A2δ transition at 284.7 nm, and observing the resulting fluorescence in the δv=0 bands at 278 nm. This detection strategy minimizes potential interferences from Raman scattering and fluorescence from other species. The O2 concentration strongly affects the sensitivity since O2 reacts rapidly with the CCl fragment before vibrational relaxation is complete. For our partially optimized apparatus and a 5-s measurement time, the detection limit for C2H5Cl mixed with, 5% O2, 15% CO2, and N2 is 100 ppb. The only interference found in flames was due to CCl produced by chemical reactions; however, its concentration is negligible except at the flame front. Interferences from flame emission were negligible, and no interfering fluorescence from other species was detected. These results indicate that our technique is capable of monitoring sub-ppm total CHC emissions from incinerators.