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(5) Pate, J. B., Ammons, B. E., Swanson,
G. A., Lodge, J. P., Jr., “Nitrite Interference in Spectrophotometric Determination of Atmospheric Sulfur
Dioxide". Anal. Chem. 37. 942 (1965). (6) Zurlo, N. and Griffini, A. M., “Measure
ment of the So, Content of Air in the Presence of Oxides of Nitrogen and Heavy Metals”, Med. Lavoro, 53, 330
(1962). (7) Scaringelli, F. P., Elfers, L., Norris, D.,
and Hochheiser, S., "Enhanced Stability of Sulfur Dioxide in Solution”,
Anal. Chem. 42, 1818 (1970). (8) Lodge, J. P. Jr., Pate, J. B., Ammons,
B. E. and Swanson, G. A., “Use of Hypodermic Needles as Critical Orifices in Air Sampling," J. Air Poll.
Cont. Assoc. 16, 197 (1966). (9) O'Keeffe, A. E., and Ortman, G. C.,
"Primary Standards for Trace Gas Analysis”. Anal. Chem. 38, 760 (1966).
(10) Scaringelli, F. P., Frey, S. A., and Saltz
man, B. E., "Evaluation of Teflon Permeation Tubes for Use with Sulfur Dioxide”, Amer. Ind. Hygiene Assoc.
J. 28, 260 (1967). (11) Scaringelli, F. P., O'Keeffe, A. E., Rosen
berg, E., and Bell, J. P., "Preparation of Known Concentrations of Gases and Vapors with Permeation Devices Calibrated Gravimetrically". Anal.
Chem. 42,871 (1970). (12) Urone, P., Evans, J. B., and Noyes, C. M.,
“Tracer Techniques in Sulfur Dioxide Colorimetric and Conductiometric Methods”, Anal Chem. 37, 1104
(1965). (13) Bostrom, C. E., “The Absorption of Sul.
fur Dioxide at Low Concentrations (p.p.m.) Studied by an Isotopic Tracer Method", Intern. J. Air Water Poll. 9, 33 (1965).
APPENDIX B-REFERENCE METHOD FOR THE
DETERMINATION OF SUSPENDED PARTICULATES
1.1 Air is drawn into a covered housing and through a filter by means of a high-flowrate blower at a flow rate (1.13 to 1.70 m.31 min.; 40 to 60 ft.3/min.) that allows suspended particles having diameters of less than 100 um. (Stokes equivalent diameter) to pass to the filter surface. (1) Particles within the size range of 100 to 0.1um. diameter are ordinarily collected on glass fiber filters. The mass concentration of suspended particulates in the ambient air (ug./m.3) is computed by measuring the mass of collected particulates and the volume of air sampled.
1.2 This method is applicable to measurement of the mass concentration of suspended particulates in ambient air. The size of the sample collected is usually adequate for other analyses.
2. Range and Sensitivity.
2.1 When the sampler is operated at an average flow rate of 1.70 m.3/min. (60 ft.3/ min.) for 24 hours, an adequate sample will be obtained even in an atmosphere having concentrations of suspended particulates as low as 1 ug./m.3. If particulate levels are unusually high, a satisfactory sample may be obtained in 6 to 8 hours or less. For determination of average concentrations of suspended particulates in ambient air, a standard sampling period of 24 hours is recommended.
2.2 Weights are determined to the nearest milligram, airflow rates are determined to the nearest 0.03 m.3/min. (1.0 ft.3/min.), times are determined to the nearest 2 minutes, and mass concentrations are reported to the nearest microgram per cubic meter.
3.1 Particulate matter that is oily, such as photochemical smog or wood smoke, may block the filter and cause a rapid drop in airflow at a nonuniform rate. Dense fog or high humidity can cause the filter to become too wet and severely reduce the airflow through the filter.
3.2 Glass-fiber filters are comparatively insensitive to changes in relative humidity, but collected particulates can be hygroscopic. (2)
4. Precision, Accuracy, and Stability.
4.1 Based upon collaborative testing, the relative standard deviation (coefficient of variation) for single analyst variation (repeatability of the method) is 3.0 percent. The corresponding value for multilaboratory variation (reproducibility of the method) is 3.7 percent. (3)
4.2 The accuracy with which the sampler measures the true average concentration depends upon the constancy of the airflow rate through the sampler. The airflow rate is affected by the concentration and the nature of the dust in the atmosphere. Under these
conditions the error in the measured average concentration may be in excess of +50 percent of the true average concentration, depending on the amount of reduction of airflow rate and on the variation of the mass concentration of dust with time during the 24-hour sampling period. (4)
5. Apparatus. 5.1 Sa
5.1.1 Sampler. The sampler consists of three units: (1) the faceplate and gasket. (2) the filter adapter assembly, and (3) the motor unit. Figure B1 shows an exploded view of these parts, their relationship to each other, and how they are assembled. The sampler must be capable of passing environmental air through a 406.5 cm.2 (63 in.2) portion of a clean 20.3 by 25.4 cm. (8- by 10-in.) glass-fiber filter at a rate of at least 1.70 m.3/min. (60 ft.3/min.). The motor must be capable of continuous operation for 24hour periods with input voltages ranging from 110 to 120 volts, 50-60 cycles alternating current and must have third-wire safety ground. The housing for the motor unit may be of any convenient construction so long as the unit remains airtight and leakfree. The life of the sampler motor can be extended by lowering the voltage by about 10 percent with a small "buck or boost" transformer between the sampler and power outlet.
5.1.2 Sampler Shelter. It is important that the sampler be properly installed in a suitable shelter. The shelter is subjected to extremes of temperature, humidity, and all types of air pollutants. For these reasons the materials of the shelter must be chosen carefully. Properly painted exterior plywood or heavy gauge aluminum serve well. The sampler must be mounted vertically in the shelter so that the glass-fiber filter is parallel with the ground. The shelter must be provided with a roof so that the filter is protected from precipitation and debris. The internal arrangement and configuration of a suitable shelter with a gable roof are shown in Figure B2. The clearance area between the main housing and the roof at its closest point should be 580.5 +193.5 cm.2 (90+30 in.2). The main housing should be rectangular, with dimensions of about 29 by 36 cm. (1112 by 14 in.).
5.1.3 Rotameter. Marked in arbitrary units, frequently 0 to 70, and capable of being calibrated. Other devices of at least comparable accuracy may be used.
5.1.4 Orifice Calibration Unit. Consisting of a metal tube 7.6 cm. (3 in.) ID and 15.9 cm. (614 in.) long with a static pressure tap 5.1 cm. (2 in.) from one end. See Figure B3. The tube end nearest the pressure tap is flanged to about 10.8 cm. (414 in.) OD with a male thread of the same size as the inlet end of the high-volume air sampler. A single metal plate 9.2 cm. (35/8 in.) in diameter and 0.24 cm. (332 in.) thick with a central orifice 2.9 cm. (1498 in.) in diameter is held in place at the air inlet end with a female threaded ring. The other end of the tube is flanged to hold a loose female threaded coupling, which screws onto the inlet of the sampler. An 18hole metal plate, an integral part of the unit, is positioned between the orifice and sampler to simulate the resistance of a clean glassfiber filter. An orifice calibration unit is shown in Figure B3.
5.1.5 Differential Manometer. Capable of measuring to at least 40 cm. (16 in.) of water.
5.1.6 Positive Displacement Meter. Cali brated in cubic meters or cubic feet, to be used as a primary standard.
5.1.7 Barometer. Capable of measuring atmospheric pressure to the nearest mm.
5.2.1 Filter Conditioning Environment. Balance room or desiccator maintained at 15° to 35°C. and less than 50 percent relative humidity.
5.2.2 Analytical Balance. Equipped with a weighing chamber designed to handle unfolded 20.3 by 25.4 cm. (8- by 10-in.) filters and having a sensitivity of 0.1 mg.
5.2.3 Light Source, Frequently a table of the type used to view X-ray films.
5.2.4 Numbering Device. Capable of printing identification numbers on the filters.
6.1 Filter Media. Glass-fiber filters having a collection efficiency of at least 99 percent for particles of 0.3 um. diameter, as measured by the DOP test, are suitable for the quantitative measurement of concentrations of suspended particulates, (5) although some other medium, such as paper, may be desirable for some analyses. If a more detailed analysis is contemplated, care must be exercised to use filters that contain low background concentrations of the pollutant being investigated. Careful quality control is required to determine background values of these pollutants.
7.1.1 Filter Preparation. Expose each filter to the light source and inspect for pinholes, particles, or other imperfections. Filters with visible imperfections should not be used. A small brush is useful for removing particles. Equilibrate the filters in the filter conditioning environment for 24 hours. Weigh the filters to the nearest milligram; record tare weight and filter identification number. Do not bend or fold the filter before collection of the sample,
7.1.2 Sample Collection. Open the shelter, loosen the wing nuts, and remove the faceplate from the filter holder. Install a numbered, preweighed, glass-fiber filter in position (rough side up), replace the faceplate without disturbing the filter, and fasten securely. Undertightening will allow air leakage, overtightening will damage the spongerubber faceplate gasket. A very light application of talcum powder may be used on the sponge-rubber faceplate gasket to prevent the filter from sticking. During inclement weather the sampler may be removed to a protected area for filter change. Close the roof of the shelter, run the sampler for about
5 minutes, connect the rotameter to the nipple on the back of the sampler, and read the rotameter ball with rotameter in a vertical position. Estimate to the nearest whole number. If the ball is fluctuating rapidly, tip the rotameter and slowly straighten it until the ball gives a constant reading. Disconnect the rotameter from the nipple; record the initial rotameter reading and the starting time and date on the filter folder, (The rotameter should never be connected to the sampler except when the flow is being measured.) Sample for 24 hours from midnight to midnight and take a final rotameter reading. Record the final rotameter reading and ending time and date on the filter folder. Remove the faceplate as described above and carefully remove the filter from the holder, touching only the outer edges. Fold the filter lengthwise so that only surfaces with collected particulates are in contact, and place in a manila folder. Record on the folder the filter number, location, and any other factors, such as meteorological conditions or razing of nearby buildings, that might affect the results. If the sample is defective, void it at this time. In order to obtain a valid sample, the high-volume sampler must be operated with the same rotameter and tubing that were used during its calibration.
7.2 Analysis. Equilibrate the exposed filters for 24 hours in the filter conditioning environment, then reweigh. After they are weighed, the filters may be saved for detailed chemical analysis.
7.3.1 Sampler Motor. Replace brushes before they are worn to the point where motor damage can occur.
7.3.2 Faceplate Gasket. Replace when the margins of samples are no longer sharp. The gasket may be sealed to the faceplate with rubber cement or double-sided adhesive tape,
7.3.3 Rotameter. Clean as required, using alcohol.
8.1 Purpose. Since only a small portion of the total air sampled passes through the rotameter during measurement, the rotameter must be calibrated against actual airflow with the orifice calibration unit. Before the orifice calibration unit can be used to calibrate the rotameter, the orifice calibration unit itself must be calibrated against the positive displacement primary standard.
8.1.1 Orifice Calibration Unit. Attach the orifice calibration unit to the intake end of the positive displacement primary standard and attach a high-volume motor blower unit to the exhaust end of the primary standard. Connect one end of a differential manometer to the differential pressure tap of the orifice calibration unit and leave the other end open to the atmosphere. Operate the high-volume motor blower unit so that a series of different, but constant, airflows (usually six) are obtained for definite time periods. Record the reading on the differential manometer at each airflow. The different constant airflows are obtained by placing a
9.2.1 Volume Conversion. Convert the inttial and final rotameter readings to true airflow rate, Q, using calibration curve of 8.1.2. 9.2.2 Calculate volume of air sampled
series of loadplates, one at a time, between the calibration unit and the primary standard. Placing the orifice before the inlet reduces the pressure at the inlet of the primary standard below atmospheric; therefore, & correction must be made for the increase in volume caused by this decreased inlet pressure. Attach one end of a second differential manameter to an inlet pressure tap of the primary standard and leave the other open to the atmosphere. During each of the constant airflow measurements made above, measure the true inlet pressure of the primary standard with this second differential manometer. Measure atmospheric pressure and temperature. Correct the measured air volume to true air volume as directed in 9.1.1, then obtain true airflow rate, Q, as directed in 9.1.3. Plot the differential manometer readings of the orifice unit versus Q.
8.1.2 High-Volume Sampler. Assemble a high-volume sampler with a clean filter in place and run for at least 5 minutes. Attach a rotameter, read the ball, adjust so that the ball reads 65, and seal the adjusting mechanism so that it cannot be changed easily. Shut off motor, remove the filter, and attach the orifice calibration unit in its place. Operate the high-volume sampler at a series of different, but constant, airflows (usually six). Record the reading of the differential manometer on the orifice calibration unit, and record the readings of the rotameter at each flow. Measure atmospheric pressure and temperature. Convert the differential manometer reading to m.3/min., Q, then plot rotameter reading versus Q.
8.1.3 Correction for Differences in Pressure or Temperature. See Addendum B.
9.1.1 True Air Volume. Calculate the air volume measured by the positive displacement primary standard.
sure, m.3 Pa=Barometric pressure, mm. Hg. Pm=Pressure drop at inlet of primary
standard, mm. Hg. Vw=Volume measured by primary stand
V=Air volume sampled, m.3
T=Sampling time, min. 9.3 Calculate mass concentration of suspended particulates
(We-W1) X 108 S.P.=
V S.P.=Mass concentration of suspended
particulates, ug/m 3 Wi=Initial weight of filter, g. Wi-Final weight of filter, g.
V=Air volume sampled, m. 108=Conversion of g. to ug. 10. References. (1) Robson, C. D., and Foster, K. E.,
“Evaluation of Air Particulate Sampling Equipment”, Am. Ind. Hyg.
ASSOC. J. 24, 404 (1962). (2) Tierney, G. P., and Conner, W. D.,
"Hygroscopic Effects on Weight Determinations of Particulates Collected on Glass-Fiber Filters", Am. Ind. Hyg.
ASSOC. J. 28, 363 (1967). (3) Unpublished data based on a collabora
tive test involving 12 participants, conducted under the direction of the Methods Standardization Services Section of the National Air Pollution Con
trol Administration, October, 1970. Harrison, W. K., Nader, J. S., and Fugman, F. S., “Constant Flow Regulators for High-Volume Air Sampler", Am.
Ind. Hyg. Assoc. J. 21, 114-120 (1960). (5) Pate, J. B., and Tabor, E. C., "Analytical
Aspects of the Use of Glass-Fiber Fil-
A modification of the high-volume sampler incorporating a method for recording the actual airflow over the entire sampling period has been described, and is acceptable for measuring the concentration of suspended particulates (Henderson, J. S., Eighth Conference on Methods in Air Pollution and Industrial Hygiene Studies, 1967, Oakland, Calif.). This modification consists of an exhaust orifice meter assembly connected through a transducer to a system for continuously recording airflow on a circular chart. The volume of air sampled is calculated by the following equation: