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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 subtinuous Measurement of Carbon

ject to revision, and additional primary Monoxide in the Atmosphere (Non- and secondary standards may be promul

dispersive Infrared Spectrometry). Appendix D-Reference Method for the

gated as the Administrator deems necesMeasurement 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

more stringent than

the

national otherwise noted.

standards. $ 50.1 Definitions.

§ 50.3 Reference conditions. (a) As used in this part, all terms not defined herein shall have the meaning

All measurements of air quality are

corrected to a reference temperature of given them by the Act.

25° C. and to a reference pressure of 760 (b) “Act” means the Clean Air Act, as amended (42 U.S.C. 1857–18571,

millimeters of mercury (1,013.2 millias

bars). amended by Pub. L. 91-604). (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 satisfaction to have a consistent relationship to

$ 50.5 National secondary ambient air

quality standards for sulfur oxides the reference method.

(sulfur dioxide). $ 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.

a

(b) 260 micrograms per cubic meter (0.1. p.p.m.)-maximum 24-hour concentration not to be exceeded more than once per year, as a guide to be used in assessing implementation plans to achieve the annual standard.

(c) 1,300 m ograms per cubic meter (0.5 p.p.m.)-maximum 3-hour concentration not to be exceeded more than once per year. 8 50.6 National primary ambient air

quality standards for particulate

matter. The national primary ambient air quality standards for particulate matter, measured by the reference method described in Appendix B to this part, or by an equivalent method, are:

(a) 75 micrograms per cubic meterannual geometric mean.

(b) 260 micrograms per cubic metermaximum 24-hour concentration not to be exceeded more than once per year. § 50.7

National secondary ambient air quality standards for particulate

matter. The national secondary ambient air quality standards for particulate matter, measured by the reference method described in Appendix B to this part, or by an equivalent method, are:

(a) 60 micrograms per cubic meterannual geometric mean, as a guide to be used in assessing implementation plans to achieve the 24-hour standard.

(b) 150 micrograms per cubic metermaximum 24-hour concentration not to be exceeded more than once per year. § 50.8 National primary and secondary

ambient air quality standards for car

bon monoxide. The national primary and secondary ambient air quality standards for carbon monoxide, measured by the reference method described in Appendix C to this part, or by an equivalent method, are:

(a) 10 milligrams per cubic meter (9 p.p.m.) —maximum 8-hour concentration not to be exceeded more than once per year.

(b) 40 milligrams per cubic meter (35 p.p.m.)-maximum 1-hour concentration not to be exceeded more than once per year. $ 50.9

National primary and secondary ambient air quality standards for

photochemical oxidants. The national primary and secondary ambient air quality standard for photo

chemical oxidants, measured and corrected for interferences due to nitrogen oxides and sulfur dioxide by the reference method described in Appendix D to this part, or by an equivalent method, is: 160 micrograms per cubic meter (0.08 p.p.m.)-maximum 1-hour concentration not to be exceeded more than once per year. § 50.10 National primary and second

ary ambient air quality standard for

hydrocarbons. The hydrocarbons standard is for use as a guide in devising implementation plans to achieve oxidant standards.

The national primary and secondary ambient air quality standard for hydrocarbons, measured and corrected for methane by the reference method described in Appendix E to this part, or by an equivalent method, is: 160 micrograms per cubic meter (0.24 p.p.m.)-maximum 3-hour concentration (6 to 9 a.m.) not to be exceeded more than once per year. $ 50.11 National primary and second

ary ambient air quality standard for

nitrogen dioxide. The national primary and secondary ambient air quality standard for nitrogen dioxide, measured by the reference method described in Appendix F to this part, or by an equivalent method, is: 100 micrograms per cubic meter (0.05 p.p.m.)-annual arithmetic mean. APPENDIX A-REFERENCE METHOD FOR THE

DETERMINATION OF SULFUR DIOXIDE IN THE ATMOSPHERE (PARAROSANILINE METHOD)

1. Principle and Applicability. 1.1 Sulfur dioxide is absorbed from air in a solution of potassium tetrachloromercurate (TCM). A dichlorosulfitomercurate complex, which resists oxidation by the oxygen in the air, is formed (1, 2). Once formed, this complex is stable to strong oxidants (e.g., ozone, oxides of nitrogen). The complex is reacted with pararosaniline and formaldehyde to form intensely colored pararosaniline methyl sulfonic acid (3). The absorbance of the solution is measured spectrophotometrically.

1.2 The method is applicable to the measurement of sulfur dioxide in ambient air using sampling periods up to 24 hours.

2. Range and Sensitivity. 2.1 Concentrations of sulfur dioxide in the range of 25 to 1,050 ug/m.3 (0.01 to 0.40 p.p.m.) can be measured under the conditions given. One can measure concentrations below 25 u8./m.3 by sampling larger volumes of air, but only if the absorption efficiency of the particular system is first determined. Higher concentrations can be analyzed by using smaller gas samples, a larger collection volume, or a suitable aliquot of the collected sample. Beer's

10

Law is followed through the working range used to give a flow of about 0.2 liter/minute. from 0.03 to 1.0 absorbance units (0.8 to 27 Use a membrane filter to protect the needle ug. of sulfite ion in 25 ml. final solution com- (Figure Ala). puted as SO2).

5.2 Analysis. 2.2 The lower limit of detection of sulfur 5.2.1 Spectrophotometer. Suitable for dioxide in 10 ml. TCM is 0.75 ug. (based on measurement of absorbance at 548 nm. with twice the standard deviation) representing a an effective spectral band width of less than concentration of 25 mg./m 80, (0.01 p.p.m.) 15 nm. Reagent blank problems may occur in an air sample of 30 liters.

with spectrophotometers having greater 3. Interferences. 3.1 The effects of the spectral band width. The wavelength caliprincipal known interferences have been bration of the instrument should be verified. minimized or eliminated. Interferences by If transmittance is measured, this can be oxides of nitrogen are eliminated by sulfamic converted to absorbance: acid (4, 5), ozone by time-delay (6), and

A=log,(1/T) heavy metals by EDTA (ethylenediaminetetraacetic acid, disodium salt) and phos

6. Reagents. phoric acid (4, 6,). At least 60 mg. Fe (III),

6.1 Sampling

6.1.1 Distilled water. Must be free from 10 ug. Mn(II), and 10 ug. Cr(III) in 10 ml. absorbing reagent can be tolerated in the

oxidants. procedure. No significant interference was 6.1.2 Absorbing Reagent (0.04 M Potasfound with 10 ug. Cu (II) and 22 ug. V(V).

sium Tetrachloromercurate (TCM)). Dissolve 4. Precision, Accuracy, and Stability. 4.1

10.86 g. mercuric chloride, 0.066 g. EDTA Relative standard deviation at the 95 percent

(ethylenediaminetetraacetic acid, disodium confidence level is 4.6 percent for the ana

salt), and 6.0 g. potassium chloride in water lytical procedure using standard samples. (5)

and bring to mark in a 1,000-ml. volumetric 4.2 After sample collection the solutions

flask. (Caution: highly poisonous. If spilled are relatively stable. At 22° C. losses of sulfur

on skin, flush off with water immediately). dioxide occur at the rate of 1 percent per

The pH of this reagent should be approxiday. When samples are stored at 5° C. for

mately 4.0, but it has been shown that there 30 days, no detectable losses of sulfur diox

is no appreciable difference in collection

efficiency over the range of pH 5 to pH 3.(7) ide occur. The presence of EDTA enhances the stability of SO2 in solution, and the rate

The absorbing reagent is normally stable for of decay is independent of the concentration

6 months. If a precipitate forms, discard the of SO2. (7)

reagent.

6.2 Analysis. 5. Apparatus. 5.1 Sampling.

6.2.1 Sulfamic Acid (0.6 percent). Dis5.1.1 Absorber. Absorbers normally used

solve 0.6 g. sulfamic acid in 100 ml. distilled in air pollution sampling are acceptable for

water. Prepare fresh daily. concentrations above 25 ug./m.: (0.01 p.p.m.).

6.2.2 Formaldehyde (0.2 percent). Dilute An all-glass midget impinger, as shown in

5 ml. formaldehyde solution (36–38 percent)

to 1,000 ml. with distilled water. Prepare Figure Al, is recommended for 30-minute and 1-hour samples.

daily.

6.2.3 For 24-hour sampling, assemble an ab

Stock Iodine Solution (0.1 N). Place sorber from the following parts:

12.7 g. iodine in a 250-ml. beaker; add 40 g. Polypropylene 2-port tube closures, special

potassium iodide and 25 ml. water. Stir until manufacture (available from Bel-Art Prod

all is dissolved, then dilute to 1,000 ml. with

distilled water. ucts, Pequannock, N.J.). Glass impingers, 6 mm. tubing, 6 inches

6.2.4 Iodine Solution (0.01 N). Prepare long, one end drawn to small diameter such approximately 0.01 N iodine solution by dithat No. 79 jewelers drill will pass through,

luting 50 ml. of stock solution to 500 ml.

with distilled water. but No. 78 jewelers drill will not. (Other end fire polished.)

6.2.5 Starch Indicator Solution. Triturate Polypropylene tubes, 164 by 32 mm. (Nal

0.4 g. soluble starch and 0.002 g. mercuric gene or equal).

iodide (preservative) with a little water, and 5.1.2 Pump. Capable of maintaining an

add the paste slowly to 200 ml. boiling water. air pressure differential greater than 0.7 at

Continue boiling until the solution is clear; mosphere at the desired flow rate.

cool, and transfer to a glass-stoppered bottle. 5.1.3 Air Flowmeter or Critical Orifice.

6.2.6 Stock Sodium Thiosulfate Solution A calibrated rotameter or critical orifice ca- (0.1 N). Prepare a stock solution by dissolving pable of measuring air flow within +2 per

25 g. sodium thiosulfate (Na2S2O3:5H20) in cent. For 30-minute sampling, a 22-gauge 1,000 rnl. freshly boiled, cooled, distilled water hypodermic needle 1 inch long may be used and add 0.1 g. sodium carbonate to the soluas a critical orifice to give a flow of about 1 tion. Allow the solution to stand 1 day before liter/minute. For 1-hour sampling, a 23- standardizing. To standardize, accurately gauge hypodermic needle five-eighths of an weigh, to the nearest 0.1 mg., 1.5 g. primary inch long may be used as a critical orifice to standard potassium iodate dried at 180° C. give a flow of about 0.5 liter/minute. For and dilute to volume in a 500-ml. volumetric 24 hour sampling, a 27-gauge hypodermic flask. To a 500-ml. iodine flask, pipet 50 ml. needle three-eighths of an inch long may be of iodate 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 a pale yellow. Add 5 ml. starch indicator solution and continue the titration until the blue color disappears. Calculate the normality

of the stock solution:

N=-X 2.80

M N=Normality of stock thiosulfate solu

tion. M=Volume of thiosulfate required, ml. W=Weight of potassium iodate, grams.

103 (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). Dilute 100 ml. of the stock thiosulfate solution to 1,000 ml, with freshly boiled distilled water. Normality=Normality of stock solution

x 0.100. 6.2.8 Standardized Sulfite Solution for Preparation of Working Sulfite-TCM Solution. Dissolve 0.3 g. sodium metabisulfite (Na,s,0z) or 0.40 g. sodium sulfite (Na2SO3) in 500 ml. of recently boiled, cooled, distilled water. (Sulfite 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 ug./ml. of SO2. The actual concentration of the solution is determined by adding excess iodine 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. iodine flasks (A and B). To flask A (blank) add 25 ml. distilled water, and to flask B (sample) pipet 25 ml. sulfite 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 a buret containing standardized 0.01 N thiosulfate, 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 concentration of sulfur dioxide in the working solution:

(A – B) (N) (32,000) ug SO2/ml.=

X 0.02

have a wavelength of maximum absorbance at 540 nm. when assayed in a buffered solution 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 calibration curve (Section 8.2.1) should have a slope of 0.030+0.002 absorbance units/ug. SO, at this path length when the dye is pure and the sulfite solution is properly standardized.

6.2.10.2 Preparation of Stock Solution. A specially purified (99–100 percent pure) solution of pararosaniline, which meets the above specifications, is commercially available in the required 0.20 percent concentration (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 a 250ml. volumetric flask, add 20 ml. stock pararosaniline 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. Procedure.

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 a midget impinger into the sampling system, Figure A1. 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 A1, 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 foil, to prevent deterioration. Determine the volume of air

25

A=Volume thiosulfate for blank, ml.
B=Volume thiosulfate for sample, ml.

N=Normality of thiosulfate titrant. 32,000=Milliequivalent wt. of SO2, ug. 25=Volume standard sulfite solution,

ml. 0.02=Dilution factor. This solution is stable for 30 days if kept at 5° C. (refrigerator). If not kept at 5° C., prepare daily.

6.2.10 Purified Pararosaniline Stock Solution (0.2 percent nominal).

6.2.10.1 Dye Specifications. The pararosaniline 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. If 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 if meaningful corrections can be applied. If storage is necessary, refrigerate at 5° C. (see 4.2).

7.2 Analysis.

7.2.1 Sample Preparation. After collection, if a precipitate is observed in the sample, remove it by centrifugation,

7.2.1.1 30-Minute and 1-Hour Samples. Transfer the sample quantitatively to a 25ml. volumetric flask; use about 5 ml, distilled water for rinsing. Delay analyses for 20 minutes to allow any ozone to decompose.

7.2.1.2 24-Hour Sample. Dilute the entire sample to 50 ml. with absorbing solution. Pipet 5 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 a reagent blank by adding 10 ml. unexposed TCM solution to a 25ml. volumetric flask. Prepare a control solution by adding ml. of working sulfite-TCM solution and 8 ml. TCM solution to a 25-ml. volumetric flask. To each flask containing either sample, control solution, or reagent blank, add 1 ml. 0.6 percent sulfamic 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 5 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, determine the absorbances of the sample (denote as A), reagent blank (denote as 1o) 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 a 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 calibration temperature (8.2), the reagent blank should be within 0.03 absorbance unit of the y-intercept of the calibration curve (8.2). If the reagent blank differs by more than 0.03 absorbance unit from that found in the calibration curve, prepare a new curve.

7.2.3 Absorbance Range. If the absorbance of the sample solution ranges between 1.0 and 2.0, the sample can be diluted 1:1 with a portion of the reagent blank and read within a few minutes. Solutions with higher absorbance can be diluted up to sixfold 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 a 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 sufficient 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 maximum 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 calibration and the temperature of analysis must be within 2 degrees. Plot the absorbance against the total concentration in ug. SO2 for the corresponding solution. The total ug. SO2 in solution equals the concentration of the standard (Section 6.2.9) in ug. SO2/ml. times the ml. sulfite solution added (ug. SO2= ug./ml. SO2X ml. added). A linear relationship should be obtained, and the y-intercept should be within 0.03 absorbance unit of the zero standard absorbance. For maximum precision determine the line of best fit using regression analysis by the method of least squares. Determine the slope of the line of best fit, calculate its reciprocal and denote as Bs. Bs is the calibration factor. (See Section 6.2.10.1 for specifications on the slope of the calibration 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 SO2 for each series of determinations, is recommended to insure the reliability of this factor.

8.2.2 Procedure with SO2 Permeation Tubes.

8.2.2.1 General Considerations. Atmospheres containing accurately known amounts

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