operates a very sophisticated airflow calibration laboratory can
calibrate its air samplers and airflow calibrators to any of four
recognized reference standards for gas volume determinations.
Furthermore, those results are traceable to the National Institue of
Standards and Technology (NIST).
Why is this important?The laws of physics for ideal gases establish that the volume of an ideal gas is a function of the temperature and pressure of the environment. One can refer to Charles' Law, Boyles' Law, and Avogadro's Law for the technical details that establish these principles.
Air sampling specialists worldwide are sampling at many different elevations and at different temperatures, and their sampling systems have variable pressure drop characteristics related to filter selection, air circuitry design and dust loading, if any.
Rarely can any two sample volume measurements be performed at the same temperature and pressure conditions.
According to the ideal gas laws of physics, two different volumes of an ideal gas can only be accurately compared if they are under the same temperature and pressure conditions. Thus, when two(2) air sample events occur at the same location but at different times or take place at different locations, the volumes determined for the air passing through the filter system need to be corrected to the same temperature and pressure conditions in order to achieve an accurate comparision of the measured values.
The accuracy of the comparison between any two or more samples is lower as sample duration increases. Generally, weekly or bi-monthly samples will be less accurate in their comparison than short-term samples of a few hours or less.
What can the air monitoring specialists do about this problem?
The solution to the problem lies in using air sampling/monitoring instruments that possess the technology to correct any sample volume determinations to a pre-determined reference temperature (T) and pressure (P). These reference conditions for T and P can properly document the results of monitoring data reported to management or regulatory agencies.
Does it matter what the reference temperature (T) and pressure (P) are?
No, it doesn't as long as the reported results are provided along with the reference T and P data. We recommend air monitoring specialists to select from one of the four recognized reference standards mentioned in the company overview.
What is the effect of radioactivity (or pollutant) concentrations upon calculations if the volumes are not corrected?
Downstream calculations involving the combination of a radioactivity (or pollutant) measurement, such as activity (Bq) in the material collected on the filter with a measured volume (m3) that has not been corrected to a reference T and P to compute a concentration (Bq/m3) can not be accurately compared to any other concentration measurement performed on a different system.
It is irrelevant whether the concentration is determined in a continuous air monitor or derived by collecting an air sample and taking the filter to the radiochemistry laboratory for analysis. The problem remains the same.
Are there air sampling systems and airflow calibration systems available on the market to address the issues raised above?
Yes, F&J SPECIALTY PRODUCTS, INC. and other technically
qualified firms in the air sampling/monitoring field have instruments
that provide air monitoring specialists with a technically acceptable
solution for this scientific need to have accurate, credible and
comparable volume determinations.