4.2.1 Reference or Equivalent Method Sampler
Each PM sampler used for reporting data to determine attainment of the National Ambient Air2.5 Quality Standard (NAAQS) for fine (2.5 µm) particulate matter must meet U.S. EPA standards and must be of a model designated by EPA as a reference or equivalent method. The minimum
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sampler requirements are described in the reference method (EPA 1997a) and in 40 CFR Part 53 (EPA 1997b). The PM sampler cost will vary with the manufacturer and the sophistication of2.5 the sampler. Basic considerations for sampler selection include flow control and measurement systems, maintenance requirements, reliability, ease of operation, and such additional capabilities as sequential sampling and downloading data.
Although a network may decide to use any number of different reference and designated equivalent PM monitor models, using a single model of sampler in a network minimizes the2.5 variety of spare parts required to keep the network in operation, simplifies training of operators, and adds consistency to the data reduction process. An in-house inventory of general
maintenance supplies and replacement parts is recommended. Examples include: various hand tools, laboratory wipes, soft brushes, and cotton swabs. Spare parts for the sampler may be obtained from the manufacturer or may be purchased from other suppliers.
The impactor requires a circular, 35- to 37-mm-diameter filter made of borosilicate glass with no binder. The filter pore size must be 1 to 1.5 µm and the thickness must be 300 to 500 µm. The impactor oil is tetramethyltetraphenyl-trisiloxane, single-compound diffusion oil, with the following specifications at 25 EC: vapor pressure, 2 × 10 mmHg; viscosity, 36 to 40-8
centistokes; and density, 1.06 to 1.07 g/cm .3
4.2.2 Calibration Equipment
Specialized equipment is needed to calibrate the sampler for temperature, barometric pressure, and volumetric flow measurements. At a minimum, the following equipment should be procured:
• A thermometer(s) capable of measuring ambient temperatures in a range of -30 to +45 EC,
readable to the nearest 0.1 EC. This thermometer should be referenced (ASTM 1992; EPA 1995; NIST 1986, 1988, 1989) to within an accuracy of ±0.5 EC to NIST-traceable American Society for Testing and Materials (ASTM) precision thermometers (e.g., ASTM numbers 62C, 63C, and 64C) once a year (ASTM 1995a). Multiple thermometers may be used to cover the temperature range as long as each thermometer meets the accuracy and readability specifications described above. Thermistor or thermocouple thermometers for use in the field should be calibrated against NIST-traceable thermometers. Some flexibility in these recommendations applies at sites where temperatures are extremely cold.
• A barometer capable of measuring barometric pressure (ASTM 1995b) over a range of 600
to 800 mm Hg (80 to 106 kiloPascals [kPa]) and readable to the nearest 1 mmHg. At least once a year, this barometer should be calibrated to within ±5 mmHg of a NIST-traceable barometer of known accuracy. A portable, aneroid barometer (e.g., a climber’s or engineer’s altimeter) is suitable for field use. A Fortin-type, mercury-column barometer may also be useful for laboratory checks of the barometer used for field measurements.
• Flow rate measurement equipment (transfer standards) capable of calibrating or verifying the
sampler’s flow rate measurement device with an accuracy of ±2 percent. This flow rate standard must be a separate, stand-alone device. It must have its own certification and be traceable to a NIST primary standard for volume or flow rate. A variety of flow rate transfer standards, with their optimum flow ranges and their support equipment, are presented in Section 6.3.2.
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Figure 4-2. Orifice dimensions to provide approximately 1 in. of water pressure drop at
• A flow rate measurement adapter of the dimensions specified in drawing No. L-30 in
Appendix L of 40 CFR Part 50 (EPA 1997a) and described in Section 7.3.6, Appendix L, that will connect the transfer standard outlet to the PM sampler flow path entering the2.5 impactor assembly and form a leak-free seal. All interconnecting tubing should be flexible and crimp-resistant. This adapter is also used in conducting the required external leak test.
4.2.3 Flow Verification Check Device
As part of the quality control (QC) procedures, a flow verification check device is required to verify that the PM sampler is operating at the correct flow rate. Figure 4-2 shows the2.5 construction details for an inexpensive and rugged QC flow verification check device that is based on measurement of the pressure drop across an orifice. This device is intended for use with a water manometer or other differential pressure meter that reads in inches of water. Note: Proper calibration of the orifice should be conducted in order to accurately predict the device’s response to variations in ambient temperature and pressure. Orifices may be calibrated using a NIST-traceable soap-bubble flowmeter of appropriate range (Nelson 1992) or other suitable NIST-traceable volumetric or flow rate standard. Other calibrated volumetric flow rate devices such as the flow rate transfer standards described in Section 6.3.2 may also be used to check flow rates during routine operation.
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Audit equipment should be similar to the calibration equipment described above. However, all audit equipment must not be the same equipment used for calibration and flow verification checks, although both sets of equipment may be of identical makes and models (see 40 CFR Part 58, Appendix A, Section 3.5.1.2). However, the calibration equipment and the audit equipment must be referenced to the same NIST primary standard for volume or flow rate.