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Appendix A-Reference Method for the De- are necessary, with an adequate margin termination of Sulfur Dioxide in
of safety, to protect the public health. the Atmosphere (Pararosaniline
National secondary ambient air quality Method).
standards define levels of air quality Appendix B-Reference Method for the Determination of Suspended Particu
which the Administrator judges neceslates in the Atmosphere (High Vol. sary to protect the public welfare from ume Method).
any known or anticipated adverse effects Appendix C-Reference Method for the con of a pollutant. Such standards are sub
tinuous Measurement of Carbon ject to revision, and additional primary Monoxide in the Atmosphere (Non
and secondary standards may be promul. dispersive Infrared Spectrometry).
gated as the Administrator deems necesAppendix D-Reference Method for the Measurement of Photochemical
sary to protect the public health and Oxidants Corrected for Interfer
welfare. ences Due to Nitrogen Oxide and (c) The promulgation of national Sulfur Dioxide.
primary and secondary ambient air qualAppendix E-Reference Method for the De. ity standards shall not be considered in termination of Hydrocarbons Cor.
any manner to allow significant deteriorected for Methane.
ration of existing air quality in any porAppendix F-Reference Method for the Determination of Nitrogen Dioxide
tion of any State. (24-Hour Sampling Method).
(d) The proposal, promulgation, or
revision of national primary and secondAUTHORITY: The provisions of this part 50 issued under sec. 4, Public Law 91-604, 84
ary ambient air quality standards shall Stat. 1679.
not prohibit any State from establishing
ambient air quality standards for that SOURCE: The provisions of this part 50 ap
State or any portion thereof which are pear at 36 F.R. 22384, Nov. 25, 1971, unless otherwise noted.
more stringent than the national
standards. 8 50.1 Definitions.
& 50.3 Reference conditions. (a) As used in this part, all terms not
All measurements of air quality are defined herein shall have the meaning
corrected to a reference temperature of given them by the Act.
(b) “Act" means the Clean Air Act, as 25° C. and to a reference pressure of 760 amended (42 U.S.C. 1857–18571, as
millimeters of mercury (1,013.2 milliamended by Pub. L. 91-604).
bars). (c) "Agency" means the Environ. & 50.4 National primary ambient airmental Protection Agency.
quality standards for sulfur oxides (d) "Administrator" means the Ad
(sulfur dioxide). ministrator of the Environmental Pro
The national primary ambient air tection Agency.
quality standards for sulfur oxides, (e) “Ambient air" means that portion
measured as sulfur dioxide by the referof the atmosphere, external to buildings,
ence method described in Appendix A to to which the general public has access.
this part, or by an equivalent method, (f) "Reference method" means &
are: method of sampling and analyzing for
(a) 80 micrograms per cubic meter an air pollutant, as described in an ap
(0.03 p.p.m.)--annual arithmetic mean, pendix to this part.
(b) 365 micrograms per cubic meter (g) "Equivalent method” means any
(0.14 p.p.m.)-Maximum 24-hour conmethod of sampling and analyzing for
centration not to be exceeded more than an air pollutant which can be demon
once per year. strated to the Administrator's satisfac
$ 50.5 National secondary ambient airtion to have a consistent relationship to
quality standards for sulfur oxides the reference method.
(sulfur dioxide). 8 50.2 Scope.
The national secondary ambient air (a) National primary and secondary quality standards for sulfur oxides, ambient air quality standards under sec measured as sulfur dioxide by the refertion 109 of the Act are set forth in this ence method described in Appendix A to part.
this part, or by an equivalent method, (b) National primary ambient air are: quality standards define levels of air (a) 60 micrograms per cubic meter quality which the Administrator judges (0.02 p.p.m.) -annual arithmetic mean. (b) 260 micrograms per cubic meter chemical oxidants, measured and cor(0.1. p.p.m.)-maximum 24-hour con- rected for interferences due to nitrogen centration not to be exceeded more than oxides and sulfur dioxide by the reference once per year, as a guide to be used in method described in Appendix D to this assessing implementation plans to achieve part, or by an equivalent method, is: 160 the annual standard.
micrograms per cubic meter (0.08 (c) 1,300 micrograms per cubic meter p.p.m.)-maximum 1-hour concentra(0.5 p.p.m.)-maximum 3-hour concen tion not to be exceeded more than once tration not to be exceeded more than per year. once per year.
$ 50.10 National primary and second$ 50.6 National primary ambient air ary ambient air quality standard for
quality standards for particulate hydrocarbons.
The hydrocarbons standard is for use The national primary ambient air as a guide in devising implementation quality standards for particulate matter, plans to achieve oxidant standards. measured by the reference method de The national primary and secondary scribed in Appendix B to this part, or by ambient air quality standard for hydroan equivalent method, are:
carbons, measured and corrected for (a) 75 micrograms per cubic meter methane by the reference method deannual geometric mean.
scribed in Appendix E to this part, or by (b) 260 micrograms per cubic meter an equivalent method, is: 160 micrograms maximum 24-hour concentration not to per cubic meter (0.24 p.p.m.)-maximum be exceeded more than once per year. 3-hour concentration (6 to 9 a.m.) not to 3 50.7 National secondary ambient air
be exceeded more than once per year. quality standards for particulate $ 50.11 National primary and secondmatter.
ary ambient air quality standard for The national secondary ambient air
nitrogen dioxide. quality standards for particulate matter, The national primary and secondary measured by the reference method de ambient air quality standard for nitrogen scribed in Appendix B to this part, or by dioxide, measured by the reference an equivalent method, are:
method described in Appendix F to this (8) 60 micrograms per cubic meter part, or by an equivalent method, is: 100 annual geometric mean, as a guide to be micrograms per cubic meter (0.05 used in assessing implementation plans to p.p.m.) -annual arithmetic mean. achieve the 24-hour standard.
APPENDIX A REFERENCE METHOD FOR THE (b) 150 micrograms per cubic meter
DETERMINATION OF SULFUR DIOXIDE IN THE maximum 24-hour concentration not to ATMOSPHERE (PARAROSANILINE METHOD) be exceeded more than once per year.
1. Principle and Applicability. 1.1 Sulfur $ 50.8 National primary and secondary
dioxide is absorbed from air in a solution of
potassium tetrachloromercurate (TCM). A ambient air quality standards for car.
dichlorosulfitomercurate complex, which rebon monoxide.
sists oxidation by the oxygen in the air, is The national primary and secondary formed (1, 2). Once formed, this complex is ambient air quality standards for carbon stable to strong oxidants (e.g., ozone, oxides monoxide, measured by the reference
of nitrogen). The complex is reacted with
pararosaniline and formaldehyde to form inmethod described in Appendix C to this
tensely colored pararosaniline methyl sulpart, or by an equivalent method, are:
fonic acid (3). The absorbance of the solu2) 10 milligrams per cubic meter (9 tion is measured spectrophotometrically. p.p.m.)-maximum 8-hour concentra 1.2 The method is applicable to the meastion not to be exceeded more than once urement of sulfur dioxide in ambient air per year.
using sampling periods up to 24 hours. (b) 40 milligrams per cubic meter (35
2. Range and Sensitivity. 2.1 Concentrap.p.m.)-maximum 1-hour concentra
tions of sulfur dioxide in the range of 25 to tion not to be exceeded more than once
1,050 ug/m.: (0.01 to 0.40 p.p.m.) can be meas
ured under the conditions given. One can per year.
measure concentrations below 25 ug./m. by 50.9 National primary and secondary
sampling larger volumes of air, but only i ambient air quality standards for
the absorption efficiency of the particular sysphotochemical oxidants.
tem is first determined. Higher concentra
tions can be analyzed by using smaller gas The national primary and secondary samples, a larger collection volume, or a suitambient air quality standard for photo- able aliquot of the collected sample. Beer's
Law is followed through the working range from 0.03 to 1.0 absorbance units (0.8 to 27 ug. of sulfite lon in 25 ml, final solution computed as SO2).
2.2 The lower limit of detection of sulfur dioxide in 10 ml. TCM is 0.75 Mg. (based on twice the standard deviation) representing & concentration of 25 mg./m 80, (0.01 p.p.m.) in an air sample of 30 liters.
3. Interferences. 3.1 The effects of the principal known interferences have been minimized or eliminated. Interferences by oxides of nitrogen are eliminated by sullamic acid (4, 5), ozone by time-delay (6), and heavy metals by EDTA (ethylenedlaminetotraacetic acid, disodlum salt) and phosphoric acid (4, 6,). At least 60 ug. Fe (III), 10 mg. Mn(II), and 10 mg. Cr(III) in 10 ml. absorbing reagent can be tolerated in the procedure. No significant interference was found with 10 pg. Cu (II) and 22 kg. V(V). 4. Precision, Accuracy, and Stability. 4.1
nd stabilitu. 4.1 Relative standard deviation at the 95 percent confidence level is 4.6 percent for the ana.
For the ana. lytical procedure using standard samples. (5)
4.2 After sample collection the solutions are relatively stable. At 22• C. losses of sulfur dioxide occur at the rate of 1 percent per day. When samples are stored at 5° C. for 30 days, no detectable losses of sulfur dioxide occur. The presence of EDTA enhances the stability of So, in solution, and the rate of decay is independent of the concentration of BO.. (7)
6.1.1 Absorber. Absorbers normally used in air pollution sampling are acceptable for concentrations above 25 wg./m.: (0.01 p.p.m.). An all-glass midget impinger, as shown in Figure Al, is recommended for 30-minute and 1-hour samples.
For 24-hour sampling, assemble an absorber from the following parts:
Polypropylene 2-port tube closures, special manufacture (avallable from Bel-Art Products, Pequannock, N.J.).
Glass impingers, 6 mm. tubing, 6 inches long, one end drawn to small diameter such that No. 79 jewelers drill will pass through, but No. 78 Jewelers drill will not. (Other end fire polished.)
Polypropylene tubes, 164 by 32 mm. (Nalgene or equal).
5.1.2 Pump. Capable of maintaining an air pressure differential greater than 0.7 atmosphere at the desired flow rate.
5.1.3 Air Flowmeter or Critical Orifice. A callbrated rotameter or critical orifice ca. pable of measuring air flow within +2 percent. For 30-minute sampling, a 22-gauge hypodermic needle 1 inch long may be used as a critical orifice to give a flow of about 1 liter/minute. For 1-hour sampling, a 23gauge hypodermic needle five-eighths of an inch long may be used as a critical orifice to give & flow of about 0.5 liter/minute. For 24 hour sampling, a 27-gauge hypodermic needle three-eighths of an inch long may be
used to give & flow of about 0.2 liter/minute. Use & membrane filter to protect the needle (Figure Ala).
5.2.1 Spectrophotometer. Suitable for measurement of absorbance at 548 nm. with an effective spectral band width of less than 16 nm. Reagent blank problems may occur with spectrophotometers having greater spectral band width. The wavelength callbration of the instrument should be verified. If transmittance is measured, this can be converted to absorbance:
A=logo(1/T) 6. Reagents. 6.1 Sampling.
6.1.1 Distilled water. Must be free from oxidants.
6.1.2 Absorbing Reagent (0.04 M Potassium Tetrachloromercurate (TCM)). Dissolve 10.86 g. mercuric chloride, 0.066 g. EDTA (ethylenediaminetetraacetic acid, disodium salt), and 6.0 g. potassium chloride in water and bring to mark in a 1,000-ml. volumetric flask. (Caution: highly poisonous. Ir spilled on skin, iush off with water immediately). The pH of this reagent should be approximately 4.0, but it has been shown that there is no appreciable difference in collection eficiency over the range of pH 5 to pH 3.(7) The absorbing reagent is normally stable for 6 months. II a precipitate forms, discard the reagent.
6.2 Analysis. 6.2.1 Sulfamic Acid (0.6 percent), Dissolve 0.6 g. sulfamic acid in 100 ml. distilled water. Prepare fresh dally.
6.2.2 Formaldehyde (0.2 percent). Dilute 5 ml, formaldehyde solution (36-38 percent) to 1,000 ml. with distilled water. Prepare dally.
6.2.3 Stock Iodine Solution (0.1 N). Place 12.7 g. lodine in & 250-ml. beaker; add 40 g. potassium iodide and 25 ml. water. Stir until all is dissolved, then dilute to 1,000 ml. with distilled water.
6.2.4 Iodine Solution (0.01 N). Prepare approximately 0.01 N lodine solution by diluting 50 ml, of stock solution to 500 ml. with distilled water.
6.2.5 Starch Indicator Solution. Triturato 0.4 g. soluble starch and 0.002 g. mercuric iodide (preservative) with a little water, and add the paste slowly to 200 ml. boiling water. Continue boiling until the solution is clear; cool, and transfer to a glass-stoppered bottle.
6.2.6 Stock Sodium Thiosulfate Solution (0.1 N). Prepare a stock solution by dissolving 25 g. sodium thiosulfate (Na2S2O3-5H:0) in 1,000 ml. freshly bolled, cooled, distilled water and add 0.1 g. sodium carbonate to the solu. tion. Allow the solution to stand 1 day before standardizing. To standardize, accurately weigh, to the nearest 0.1 mg., 1.5 g. primary standard potassium iodate dried at 180° C. and dilute to volume in a 500-ml. volumetric flask. To a 500-ml. iodine flask, pipet 50 ml. of lodate solution. Add 2 g. potassium iodide and 10 ml. of 1 N hydrochloric acid. Stopper the flask. After 5 minutes, titrate with stock thiosulfate solution to & pale yellow. Add 6 ml. starch indicator solution and continue the titration until the blue color disappears. Calculate the normality of the stock solution:
tion. M=Volume of thiosulfate required, ml. W=Weight of potassium iodate, grams.
10% (conversion of g. to mg.) x0.1 (fraction iodate used) 2.80 =
35.67 (equivalent weight of potassium iodate)
6.2.7 Sodium Thiosulfate Titrant (0.01 N). Dllute 100 ml. of the stock thiosulfate solu. tion to 1,000 ml. with freshly boiled distilled water. Normality=Normallty of stock solution
x 0.100. 6.2.8 Standardized Sulfite Solution for Preparation of Working Sulfte-TCM Solution. Dissolve 0.3 g. sodium metabisulfite (Na 8,0%) or 0.40 8. sodium sulfite (NA,SO,) in 500 ml. of recently bolled, cooled, distilled water. (Sulate solution is unstable; it is therefore important to use water of the highest purity to minimize this instability.) This solution contains the equivalent of 320 to 400 13./ml. of sog. The actual concentration of the solution is determined by adding excess lodine and back-titrating with standard sodium thiosulfate solution. To back-titrate, pipet 50 ml. of the 0.01 N iodine into each of two 500-ml. lodine flasks (A and B). To flask A (blank) add 25 ml. distilled water, and to flask B (sample) pipet 25 ml. sulfte solution. Stopper the flasks and allow to react for 5 minutes. Prepare the working sulfite-TCM Solution (6.2.9) at the same time iodine solution is added to the flasks. By means of
buret containing standardized 0.01 N thio. sulfate, titrate each flask in turn to a pale yellow. Then add 5 ml. starch solution and continue the titration until the blue color disappears.
6.2.9 Working Sulfite-TCM Solution. Pipet accurately 2 ml. of the standard solution into a 100 ml volumetric flask and bring to mark with 0.04 M TCM. Calculate the concentra. tion of sulfur dioxide in the working solution:
have & wavelength of maximum absorbance at 540 am. when assayed in a buffered solu. tion of 0.1 M sodium acetate-acetic acid; (2) the absorbance of the reagent blank, which is temperature-sensitive (0.015 absorbance unit/°C), should not exceed 0.170 absorbance unit at 22°C. with a 1-cm. optical path length, when the blank is prepared according to the prescribed analytical procedure and to the specified concentration of the dye; (3) the callbration curve (Section 8.2.1) should have & slope of 0.030+0.002 absorbance units/ug. So, at this path length when the dye is pure and the sulfte solution 18 properly standardized.
126.96.36.199 Preparation of Stock Solution, A specially purified (99–100 percent pure) 80lution of pararosaniline, which meets the above specifications, is commercially avall. able in the required 0.20 percent concen. tration (Harleco*). Alternatively, the dye may be purified, a stock solution prepared and then assayed according to the procedure of Scaringelli, et al. (4)
6.2.11 Pararosaniline Reagent. To & 250ml. volumetric flask, add 20 ml. stock par. arosaniline solution. Add an additional 0.2 ml. stock solution for each percent the stock assays below 100 percent. Then add 25 ml. 3 M phosphoric acid and dilute to volume with distilled water. This reagent is stable for at least 9 months.
7.1 Sampling. Procedures are described for short-term (30 minutes and 1 hour) and for long-term (24 hours) sampling. One can select different combinations of sampling rate and time to meet special needs. Sample volumes should be adjusted, so that linearity Is maintained between absorbance and concentration over the dynamic range.
7.1.1 30-Minute and 1-Hour Samplings. Insert & midget impinger into the sampling system, Figure Al. Add 10 ml. TCM solution to the Impinger. Collect sample at 1 liter/ minute for 30 minutes, or at 0.5 liter/minute for 1 hour, using either a rotameter, as shown in Figure Al, or a critical orifice, as shown in Figure Ala, to control flow. Shield the absorbing reagent from direct sunlight during and after sampling by covering the impinger with aluminum foll, to prevent deterioration. Determine the volume of air
B) (N) (32,000) x 0.02
26 A=Volume thiosulfate for blank, ml. B=Volume thiosulfate for sample, ml.
N=Normality of thiosulfate titrant. 32,000=Milliequivalent wt. of SO2, Mg.
25=Volume standard sulfte solution,
0.02=Dilution factor. This solution is stable for 30 days if kept at 5. C. (refrigerator). Il not kept at 5* C., prepare dally.
6.2.10 Purified Pararosaniline Stock Solu. tion (0.2 percent nominal).
188.8.131.52 Dye Specifications. The pararo. saniline dye must meet the following performance specifications: (1) the dye must
*Hartmen-Leddon, 60th and Woodland Avenue, Philadelphia, PA 19143.
sampled by multiplying the flow rate by the time in minutes and record the atmospheric pressure and temperature. Remove and stopper the impinger. I the sample must be stored for more than a day before analysis, keep it at 5° C. in a refrigerator (see 4.2).
7.1.2 . 24-Hour Sampling. Place 50 ml. TCM solution in a large absorber and collect the sample at 0.2 liter/minute for 24 hours from midnight to midnight. Make sure no entrainment of solution results with the impinger. During collection and storage protect from direct sunlight. Determine the total air volume by multiplying the air flow rate by the time in minutes. The correction of 24-hour measurements for temperature and pressure is extremely difficult and is not ordinarily done. However, the accuracy of the measurement will be improved 11 mean ingful corrections can be applied. II storage is necessary, refrigerate at 5° C. (see 4.2).
7.2.1 Sample Preparation. After collection, 1f a precipitate is observed in the sample, remove it by centrifugation.
184.108.40.206 30-Minute and 1-Hour Samples. Transfer the sample quantitatively to a 25ml. volumetric flask; use about 5 mi, distilled water for rinsing. Delay analyses for 20 min. utes to allow any ozone to decompose.
220.127.116.11 24-Hour Sample. Dilute the entire sample to 60 ml. with absorbing solution, Pipet 6 ml. of the sample into a 25-ml. volumetric flask for chemical analyses. Bring volume to 10 ml. with absorbing reagent. Delay analyses for 20 minutes to allow any ozone to decompose.
7.2.2 Determination. For each set of determinations prepare & reagent blank by addIng 10 ml. unexposed TCM solution to a 25ml. volumetric flask. Prepare a control solu. tion by adding 2 ml. of working sulfite-TCM solution and 8 ml, TCM solution to & 25-ml. volumetric flask. To each flask containing etther sample, control solution, or reagent blank, add 1 ml. 0.6 percent sullamic acid and allow to react 10 minutes to destroy the nitrite from oxides of nitrogen. Accurately pipet in 2 ml. 0.2 percent formaldehyde solution, then 6 ml. pararosaniline solution. Start a laboratory timer that has been set for 30 minutes. Bring all flasks to volume with freshly boiled and cooled distilled water and mix thoroughly. After 30 minutes and before 60 minutes, des termine the absorbances of the sample (denote as A), reagent blank (denote as to) and the control solution at 548 nm. using 1-cm. optical path length cells. Use distilled water, not the reagent blank, as the reference. (NOTE! This is important because of the color sensitivity of the reagent blank to temperature changes which can be induced in the cell compartment of a spectrophotometer.) Do not allow the colored solution to stand
in the absorbance cells, because & film of dye may be deposited. Clean cells with alcohol after use. If the temperature of the determinations does not differ by more than 2° C. from the callbration temperature (8.2), the reagent blank should be within 0.03 absorbance unit of the y-intercept of the calibration curve (8.2). the reagent blank differs by more than 0.03 absorbance unit from that found in the calibration curve, prepare a new curve.
7.2.8 Absorbance Range. If the absorbance of the sample solution ranges between 1.0 and 2.0, the sample can be diluted 1:1 with & portion of the reagent blank and read within a few minutes. Solutions with higher absorbance can be diluted up to sixtold with the reagent blank in order to obtain onscale readings within 10 percent of the true absorbance value.
8. Calibration and Efficiencies.
8.1 Flowmeters and Hypodermic Needle. Calibrate flowmeters and hypodermic needle (8) against & calibrated wet test meter.
8.2 Calibration Curves.
8.2.1 Procedure with Sulfite Solution. Accurately pipet graduated amounts of the working sulfite-TCM solution (6.2.9) (such as 0, 0.5, 1, 2, 3, and 4 ml.) into a series of 25-ml. volumetric flasks. Add suficient TCM solution to each flask to bring the volume to approximately 10 ml. Then add the remaining reagents as described in 7.2.2. For maxmum precision use a constant-temperature bath. The temperature of calibration must be maintained within +1° C. and in the range of 20° to 30° C. The temperature of callbration and the temperature of analysis must be within 2 degrees. Plot the absorbance against the total concentration in ug. SO, for the corresponding solution. The total pg. SO, in solution equals the concentration of the standard (Section 6.2.9) in ug. SO2/ml. times the ml. sulfite solution added (ug. 80= ng./ml. SO.xml. added). A linear relation. ship should be obtained, and the y-intercept should be within 0.03 absorbance unit of the zero standard absorbance. For maximum pre. cision determine the line of best fit using regression analysis by the method of least squares. Determine the slope of the line of best it, calculate its reciprocal and denote as B.. B. is the calibration factor. (See Sectlon 18.104.22.168 for specifications on the slope of the callbration curve). This callbration factor can be used for calculating results provided there are no radical changes in temperature or pH. At least one control sample containing a known concentration of SO, for each series of determinations, is recommended to insure the reliability of this factor.
8.2.2 Procedure with SO. Permeation Tubes.
22.214.171.124 General Considerations. Atmos. pheres containing accurately known amounts