Calibration and Auditing Procedures
Discussion of Flow Rate Measurement and General Aspects of PM10/PM2.5 Sampler Calibration
A MiniVol sampler consists of three basic components: a specially designed inlet, size-fractionating impactors, and a flow rate controlling system. The particle size discrimination characteristics of both the inlet and the impactors depend critically on specified air velocities; a change in velocity will result in a change in the nominal particle size collected. For this reason, it is imperative that the flow rate through the sampler be maintained at a constant value that is as close as possible to the design flow rates. The design flow rate for the MiniVol is 5.0 L/min. The sampler's flow rate should be within ±10% of 5 L/min or 4.5 to 5.5 L/min.
As indicated above, the true or actual flow through the sampler inlet must be known and controlled to ensure that only those particles nominally less than 10 µm/2.5 µm are being collected. A common source of error in a PM10/PM2.5 monitoring program is confusion between various air measurement units. Before calibration procedures are initiated, the operating agency personnel should review the following flow rate designations:
Qact: Actual volumetric air flow rates that are measured and expressed at existing conditions of temperature and pressure are denoted by Qact (Qactual). Typical units are L/min and cubic meters per minute (m3/min). Inlet design flow rates are always given in actual volumetric flow units.
Qstd: Air flow rates that have been corrected to EPA standard conditions of temperature and pressure (25 EC or 298 EK, and 760 mm Hg or 101 kPa) are denoted by Qstd (Qstandard). Typical units are std. L/min and std. m3/min. Standard volume flow rates are often used by engineers and scientists and are equivalent to mass flow units.
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