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An Air Force-sponsored effort to develop a versatile field sensor for the measurement of hydrogen chloride (HC1) vapors from rocket launches is described. Lawrence Livermore National Laboratory (LLNL) is developing an infrared HC1 detector with ppb range sensitivities to be used for monitoring HC1 during space vehicle launches at Vandenberg AFB. HC1 deposition on the community neighboring Vandenberg AFB can involve costly litigation. Monitoring is necessary to determine the amount of HC1 and if it presents hazardous situations or detrimental effects. The Air Force currently uses MIRAN IR sensors. These instruments analyze "grab samples" so they cannot accurately determine HC1 in a quickly changing atmosphere. Analysis times are on the order of several minutes, and there is no "real time" correction for background gases such as methane and water vapor. Sensitivity is only 3 ppm and remote operation is not feasible. The sensor developed by LLNL is an "in situ" sampler, which can constantly monitor a rapidly changing concentration of HC1 in air (response time is one second). It is a four-band differential absorption instrument, allowing for corrections due to system electronic and optical variations, as well as for variations in the background concentrations of methane and water vapor that also absorb at HC1 wavelengths. There is also the possibility of measuring HC1 droplets with this type of sensor. The detector's variable pathlength-absorption region allows for HC1 detection down to 200 ppb. The instrument is remotely operable, a necessity given the rugged Vandenberg terrain and limitations placed on personnel access to the launch area. The data from the battery-powered sensor are transmitted via radio link to a central base station where they are displayed and recorded using an IBM PC.
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