Application of a Dry-Gas Meter for Measuring Air Sample Volumes in an Ambient Air Monitoring Network

Abstract

Ambient air monitoring for non-research applications (i.e., compliance) occurs throughout the world. Often, air sampling systems employed for these purposes employ simple yet robust equipment capable of handling the rigors of demanding sampling schedules and harsh environments. At the Hanford Site (near Richland, Washington) concentrations of radionuclides in ambient air are monitored continuously at 44 locations. In 2004, mechanical dry-gas meters were incorporated into the Hanford Site ambient air sample collection system to allow the direct measurement of sample volumes. These meters replaced an airflow measurement system that required two manual flow measurements and a sample duration measurement to determine sample volume. A six-month evaluation of the dry-gas meters compared sample volumes calculated using the original flow-rate method to the sample volume measured directly by the dry-gas meter. The two methods provided sample volumes that were within 15% of each other 87% of the time. The results indicated that for instances where the sample volume measured by the two methods differed by more than 15%, the dry-gas meter method provided a more accurate sample volume measurement. The results of the evaluation further indicated that the dry-gas meters provided more accurate sample volumes for all samples, resulting in greater confidence in the calculated concentration results.

Concepts for Environmental Radioactive Air Sampling and Monitoring

“…Errors in the sample volume measurement are directly proportional to errors in the calculated sample concentration (Fritz, 2009). A variety of instruments are available to measure flow and can include rotameters, electronic mass flow controllers, and venturi meters (Wight, 1994).…”

“…A variety of instruments are available to measure flow and can include rotameters, electronic mass flow controllers, and venturi meters (Wight, 1994). Fritz (2009) reported on the implementation of a dry-gas meter application to air sample volume measurements in lieu of a more cumbersome and less accurate two-point manual airflow measurement and sample duration. The new method showed improved reliability and measurement resolution, reduced error, and more accurate concentration calculations.…”