Andersen PM-10 Sampler | Ambient Particulate Samplers | Air quality testing | Air quality monitoring | Air sampling equipment

PM10 MASS Flow Controlled

In 1971, The Environmental Protection Agency (EPA) promulgated primary and secondary national ambient air quality standards for particulate matter measured as “total suspended particulate” or “TSP”. In accordance with the Clean Air Act, the EPA reviewed and revised the health and welfare criteria upon which these primary and secondary particulate matter standards were based.

On March 20, 1984 the EPA proposed changes in the standards based on it's review and revision of the criteria. On July 1, 1987 the EPA promulgated its final decisions regarding these changes. The final decisions include:

1. Replacing TSP as the indicator for particulate matter for the ambient standards with a new indicator that includes only those particles with an aerodynamic diameter less than or equal to nominally ten (10) microns (PM10).
2. A new Federal Reference method for measurement of PM10 in ambient air. The Reference method for the measurement of atmospheric particulate matter is known as PM10 and is based on selection of PM10 particles by internal separation, followed by filtration and gravimetric determination of PM10 mass on the filter substrate.

PM10 Volumetric Flow Controlled

The Volumetric Flow Controller (VFC) is a dimensional venturi device used to control gas flow. When applied to a high volume air sampler, this flow control principal incorporates a smooth-wall venturi orifice that gradually opens to a recovery section. Vacuum is provided by a motor downstream of the venturi. Over 95% of the energy lost in differential pressures across the restricting orifice is recovered in this design.

Flow control is accomplished by occluding or restricting and thus accelerating the air flow through the venturi . At some point in the flow stream, the air velocity will equal the acoustic velocity or speed of sound, and critical flow will be achieved. As long as downstream changes are small, all conditions at the venturi (including the flow rate) are determined by upstream conditions. This condition is referred to as “chocking” and is a distinctive characteristic of all VFCs. The GMW PM10/VFC utilizes this principle of choked or critical flow to maintain a constant actual flow rate of 40 ACFM (1.3ACMM) over the sample period. Since critical flow through the venturi is not greatly affected by changes in the filter loading, ambient temperature oo barometric pressure, a stable volumetric flow rate is maintained as long as power is provided to the sampler blower motor.

The orifice used in this system can also be described as a well documented Critical Venturi Meter (CVM). Basically, a CVM is a specially machined nozzle or restriction device designed to react to a specific pressure ratio expressed in absolute terms. When air reaches the speed of sound in the throat (smallest diameter) of the CVM, a sound pressure barrier is set up that will not allow more air through under the existing temperature and pressure conditions. This is the “critical flow” point of the meter, thus the name Critical Venturi Meter. Simply put, the Volumetric Flow controller regulates flow at a constant but unadjustable rate without any moving parts or electronic components. GMW PM10 Samplers bear an identification label with the FRM designation number RFPS-1287-063.