© 1988 Oxford University Press
research-article |
Evaluation of a Real-Time Aerosol Monitor (RAM-S) for Inhalation Studies
Inhalation Toxicology Research Institute, Lovelace Biomedical and Environmental Research Institute P.O. Box 5890, Albuquerque, New Mexico 87185 *National Institute of Environmental Health Sciences, Research Triangle Park North Carolina 27709
Received May 18, 1987; accepted September 9, 1987
Evaluation of a Real-Time Aerosol Monitor (RAM-S) for Inhalation Studies. CHENG, Y. S., BARR, E. B., BENSON, J. M., DAMON, E. G., MEDINSKY, M. A., HOBBS, C. H., AND GOEHL, T. J. (1988). Fundam. Appl. Toxicol. 10, 321-328. Measurement of the aerosol concentration in inhalation toxicology studies is generally done by gravimetric and/or chemical analysis of filter samples taken over a known period of time at a fixed sampling flow rate. The value obtained represents the time-averaged concentration in an exposure chamber. However, the filter method does not provide information as to the stability of aerosol concentration in "real-time" nor as to the time required for the aerosol concentration to reach the target value during the start-up of exposures. In order to accomplish evaluation of aerosol stability and chamber rise and fall times, a direct measurement device is required. An available real-time aerosol monitor (RAM-S, GCA Corp., Bedford, MA) is a photometer which collects scattered light from an aerosol cloud at a 70 ± 25° angle. The output signal is 0 to 10 volt with three ranges corresponding to maximum aerosol concentrations of 200, 20, and 2 mg/m3. The performance of the RAM-S was evaluated in inhalation studies involving nickel sulfate hexahydrate, nickel oxide, nickel subsulfide, and azodicarbonamide. Several RAM-S units were calibrated by obtaining both filter samples and voltage readings of a RAM-S simultaneously. Results indicated that the response of the RAM-S instruments was linear. However, the voltage output per given aerosol concentration was different for each compound used. Furthermore, there was interinstrument variability in the voltage response to aerosol concentration of a given compound. At concentrations higher than 100 mg/m3, modification of the flow system in the RAM-S was made to increase the sheath air around the optical system and also to dilute the aerosol concentration. The RAM-S proved to be a useful instrument for determining the stability of aerosol concentration, the rise and fall time, and the distribution of aerosol in the chamber. This instrument was complementary to the filter method for monitoring the aerosol concentration in inhalation exposure studies.