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Diffusive monitoring of fluctuating concentrations.

Bartley DL; Doemeny LJ; Taylor DG
Am Ind Hyg Assoc J 1983 Apr; 44(4):241-247
An approach to the practical sampling for the measurement of concentrations of gas and vapors by means of diffusing samplers using a cap filled with adsorbent and then estimating the concentration from the adsorbed mass on the fixed sorbent in the sampler, was described. The error introduced by the fluctuation in estimates of time weighted averages of fluctuated concentrations was analyzed for specific diffusive monitors in which the concentration at the sorbent was close to zero. The lower error was determined but no upper error could be estimated. A general formula was established for concentration estimates represented as a system response to the concentration as a function of time. For sampling pulse concentration with Palmes tubes, the error was large and depended on the sharpness of the pulses. Time dependent fluctuating concentrations for sampling periods of 15 minutes each, revealed that the 95 percent confidence level for the error was excessive. The authors conclude that in cases of short sampling time, longer sampling periods would yield acceptable errors and that for shorter sampling periods the error introduced by fluctuation could be reduced by shortening the length of the sampling tube. Further studies are recommended on sampler response to fluctuating concentrations.
NIOSH-Author; Sampling-methods; Sampling-equipment; Environmental-control-equipment; Gas-sampling; Air-sampling; Environmental-contamination; Mathematical-models
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American Industrial Hygiene Association Journal
Page last reviewed: September 2, 2020
Content source: National Institute for Occupational Safety and Health Education and Information Division