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1679 (42 U.S.C. 1857c-4). ITY STANDARDS

SOURCE: 36 FR 22384, Nov. 25, 1971, unless

otherwise noted. Sec. 50.1 Definitions.

8 50.1 Definitions. 50.2 Scope.

(a) As used in this part, all terms not 50.3 Reference conditions.

defined herein shall have the meaning 50.4 National primary ambient air quality

given them by the Act.
standards for sulfur oxides (sulfur diox-

(b) Act” means the Clean Air Act, 50.5 National secondary ambient air qual

as amended (42 U.S.C. 1857-18571, as ity standards for sulfur oxides (sulfur amended by Pub. L. 91-604). dioxide).

(c) “Agency” means the Environ50.6 National primary ambient air quality mental Protection Agency. standards for particulate matter.

(d) “Administrator" means the Ad50.7 National secondary ambient air qual

ministrator of the Environmental Proity standards for particulate matter. 50.8 National primary and secondary ambi

tection Agency. ent air quality standards for carbon

(e) “Ambient air” means that pormonoxide.

tion of the atmosphere, external to 50.9 National primary and secondary ambi buildings, to which the general public

ent air quality standards for ozone. has access. 50.10 National primary and secondary am

(f) "Reference method” means a bient air quality standard for hydrocar

method of sampling and analyzing the bons. 50.11 National primary and secondary am

ambient air for an air pollutant that is bient air quality standard for nitrogen

specified as a reference method in an dioxide.

appendix to this part, or a method 50.12 National primary and secondary am that has been designated as a refer

bient air quality standards for lead. ence method in accordance with Part APPENDIX A-REFERENCE METHOD FOR THE 53 of this chapter; it does not include a

DETERMINATION OF SULFUR DIOXIDE IN method for which a reference method
THE ATMOSPHERE (PARAROSANILINE designation has been cancelled in ac-

cordance with $ 53.11 or $ 53.16 of this APPENDIX B-REFERENCE METHOD FOR THE


(g) "Equivalent method” means a METHOD)

method of sampling and analyzing the APPENDIX C-MEASUREMENT PRINCIPLE AND ambient air for an air pollutant that

CALIBRATION PROCEDURE FOR THE CON has been designated as an equivalent
TINUOUS MEASUREMENT OF CARBON MON method in accordance with Part 53 of

this chapter; it does not include a SIVE INFRARED SPECTOMETRY)

method for which an equivalent APPENDIX D-MEASUREMENT PRINCIPLE AND

method designation has been canCALIBRATION PROCEDURE FOR THE MEA



[36 FR 22384, Nov. 25, 1971, as amended at FOR METHANE

41 FR 11253, Mar. 17, 1976)

$ 50.2 Scope.
ATMOSPHERE (GAS PHASE CHEMILUMINES (a) National primary and secondary

ambient air quality standards under APPENDIX G-REFERENCE METHOD FOR THE

section 109 of the Act are set forth in DETERMINATION OF LEAD IN SUSPENDED



quality standards define levels of air TIONAL AMBIENT AIR QUALITY STANDARDS quality which the Administrator FOR OZONE

judges are necessary, with an adequate

margin of safety, to protect the public meter (0.5 p.p.m.) maximum 3-hour health. National secondary ambient concentration not to be exceeded more air quality standards define levels of than once per year. air quality which the Administrator

(38 FR 25681, Sept. 14, 1973) judges necessary to protect the public welfare from any known or anticipat

8 50.6 National primary ambient air qualed adverse effects of a pollutant. Such standards are subject to revision, and

ity standards for particulate matter. additional primary and secondary The national primary ambient air standards may be promulgated as the quality standards for particulate Administrator deems necessary to pro- matter, measured by the reference tect the public health and welfare. method described in Appendix B to

(c) The promulgation of national this part, or by an equivalent method, primary and secondary ambient air

are: quality standards shall not be consid

(a) 75 micrograms per cubic meterered in any manner to allow signifi

annual geometric mean. cant deterioration of existing air qual

(b) 260 micrograms per cubic ity in any portion of any State.

meter-maximum 24-hour concentra(d) The proposal, promulgation, or

tion not to be exceeded more than revision of national primary and secondary ambient air quality standards

once per year. shall not prohibit any State from es

$ 50.7 National secondary ambient air tablishing ambient air quality stand

quality standards for particulate ards for that State or any portion

matter. thereof which are more stringent than the national standards.

The national secondary ambient air

quality standards for particulate 8 50.3 Reference conditions.

matter, measured by the reference All measurements of air quality are method described in Appendix B to corrected to a reference temperature this part, or by an equivalent method, of 25° C. and to a reference pressure of are: 760 millimeters of mercury (1,013.2 (a) 60 micrograms per cubic metermillibars).

annual geometric mean, as a guide to

be used in assessing implementation 8 50.4 National primary ambient air qual

plans to achieve the 24-hour standard. ity standards for sulfur oxides (sulfur

(b) 150 micrograms per cubic dioxide),

meter-maximum 24-hour concentraThe national primary ambient air tion not to be exceeded more than quality standards for sulfur oxides

once per year. measured as sulfur dioxide by the reference method described in Appendix 8 50.8 National primary and secondary A to this part, or by an equivalent ambient air quality standards for method, are:

carbon monoxide. (a) 80 micrograms per cubic meter (0.03 p.p.m.)-annual arithmetic mean.

The national primary and secondary (b) 365 micrograms per cubic meter

ambient air quality standards for (0.14 p.p.m.)-Maximum 24-hour con

carbon monoxide, measured by a refercentration not to be exceeded more

ence method based on Appendix C to than once per year.

this part and designated in accordance

with Part 53 of this chapter, or by an 8 50.5 National secondary ambient air equivalent method, are:

quality standards for sulfur oxides (a) 10 milligrams per cubic meter (9 (sulfur dioxide).

p.p.m.)-maximum 8-hour concentraThe national secondary ambient air tion not to be exceeded more than quality standard for sulfur oxide once per year. measured as sulfur dioxide by the ref. (b) 40 milligrams per cubic meter (35 erence method described in Appendix p.p.m.)-maximum 1-hour concentraA to this part, or by any equivalent tion not to be exceeded more than method is 1,300 micrograms per cubic once per year.

16 FR 22384, Nov. 25, 1971, as amended at by an equivalent method, are: 1.5 mi) FR 7043, Feb. 18, 1975)

crograms per cubic meter, maximum 50.9

arithmetic mean averaged over a calNational primary and secondary

endar quarter. ambient air quality standards for ozone.

(Secs. 109, 301(a) Clean Air Act as amended (a) The level of the national primary

(42 U.S.C. 7409, 7601(a))) nd secondary ambient air quality

(43 FR 46258, Oct. 5, 1978) tandards for ozone measured by a refrence method based on Appendix D o this part and designated in accord. APPENDIX A-REFERENCE METHOD FOR „nce with Part 53 of this chapter, is THE DETERMINATION OF SULFUR Diox1.12 part per million (235 ug/m'). The IDE IN THE ATMOSPHERE (PARAROSANItandard is attained when the expect LINE METHOD)

d number of days per calendar year vith maximum hourly average concen

1. Principle and Applicability. 1.1 Sulfur

dioxide is absorbed from air in a solution of rations above 0.12 part per million

potassium tetrachloromercurate (TCM). A 235 ug/m) is equal to or less than 1,

dichlorosulfitomercurate complex, which reis determined by Appendix H.

sists oxidation by the oxygen in the air, is Secs. 109 and 301 of the Clean Air Act, as

formed (1, 2). Once formed, this complex is amended (42 U.S.C. 7409, 7601))

stable to strong oxidants (e.g., Ozone, oxides

of nitrogen). The complex is reacted with (44 FR 8220, Feb. 8, 1979)

pararosaniline and formaldehyde to form

intensely colored pararosaniline methyl sul$ 50.10 National primary and secondary

fonic acid (3). The absorbance of the soluambient air quality standard for hydro

tion is measured spectrophotometrically. carbons.

1.2 The method is applicable to the meaThe hydrocarbons standard is for

surement of sulfur dioxide in ambient air use as a guide in devising implementa

using sampling periods up to 24 hours. tion plans to achieve oxidant stand

2. Range and Sensitivity. 2.1 Concentra

tions of sulfur dioxide in the range of 25 to ards. The national primary and sec

1,050 ug/m." (0.01 to 0.40 p.p.m.) can be ondary ambient air quality standard

measured under the conditions given. One for hydrocarbons, measured and cor- can measure concentrations below 25 ug./ rected for methane by the referencem.' by sampling larger volumes of air, but method described in Appendix E to only if the absorption efficiency of the parthis part, or by an equivalent method, ticular system is first determined. Higher is: 160 micrograms per cubic meter concentrations can be analyzed by using (0.24 p.p.m.)-maximum 3-hour con

smaller gas samples, a larger collection

volume, or a suitable aliquot of the collected centration (6 to 9 a.m.) not to be ex

sample. Beer's Law is followed through the ceeded more than once per year.

working range from 0.03 to 1.0 absorbance 8 50.11 National primary and secondary

units (0.8 to 27 ug. of sulfite ion in 25 ml.

final solution computed as SO,). ambient air quality standard for nitro

2.2 The lower limit of detection of sulfur gen dioxide.

dioxide in 10 ml. TCM is 0.75 ug. (based on The national primary and secondary

twice the standard deviation) representing a ambient air quality standard for nitro concentration of 25 mg./m 'SO, (0.01 p.p.m.) gen dioxide, measured by the refer

in an air sample of 30 liters. ence method described in Appendix F

3. Interferences. 3.1 The effects of the

principal known interferences have been to this part, or by an equivalent

minimized or eliminated. Interferences by method, is: 100 micrograms per cubic oxides of nitrogen are eliminated by sulfameter (0.05 p.p.m.)-annual arithmetic mic acid (4, 5), ozone by time-delay (6), and mean.

heavy metals by EDTA (ethylene-diamine

tetraacetic acid, disodium salt) and phos8 50.12 National primary and secondary phoric acid (4, 6). At least 60 ug. Fe (III), 10 ambient air quality standards for lead. ug. Mn (II), and 10 ug. Cr (III) in 10 ml. ab

sorbing reagent can be tolerated in the proNational primary and secondary am

cedure. No significant interference was bient air quality standards for lead

found with 10 ug. Cu (II) and 22 ug. V (V), and its compounds, measured as ele

4. Precision, Accuracy, and stability. 4.1 mental lead by a reference method Relative standard deviation at the 95 perbased on Appendix G to this part, or cent confidence level is 4.6 percent for the

analytical 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 SO2. (7)

5. Apparatus.
5.1 Sampling.

5.1.1 Absorber. Absorbers normally used in air pollution sampling are acceptable for concentrations above 25 ug./m. 3 (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, spe. cial manufacture (available 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 at mosphere at the desired flow rate.

5.1.3 Air Flowmeter or Critical Orifice. A calibrated rotameter or critical orifice capable 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 23-gauge hy. podermic needle five-eights of an inch long may be used as a critical orifice to give a 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 a flow of about 0.2 liter/minute. Use a membrane filter to protect the needle (Figure Ala).

5.2 Analysis.

5.2.1 Spectrophotometer, Suitable for mea surement of absorbance at 548 nm. with an effective spectral band width of less than 15 nm. Reagent blank problems may occur with spectrophotometers having greater spectral band width. The wavelength calibration of the instrument should be verified. If transmittance is measured, this can be converted to absorbance:

A=log,o(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 Potas. sium Tetrachloromercurate (TCM)). Dis

solve 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-r1 volumetric flask. (Caution: Highly poisor.ous. If spilled on skin, flush off with water immediately). The pH of this reagen: should be approximately 4.0, but it has been shown that there is no appreciable differ ence in collection efficiency over the range of pH 5 to pH 3.(7). The absorbing reagent is normally stable for 6 months. If a precipi tate 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 daily.

6.2.2 Formaldehyde (0.2 percent). Dilute 5 ml. formaldehyde solution (36-38 percent) to 1,000 ml. with distilled water. Prepare daily.

6.2.3 Stock Iodine Solution (0.1 N). Place 12.7 g. iodine in a 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 iodine solution by diluting 50 ml. of stock solution to 500 ml. with distilled water.

6.2.5 Starch Indicator Solution. Triturate 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 glassstoppered bottle.

6.2.6 Stock Sodium Thiosulfate Solution (0.1 N). Prepare a stock solution by dissolving 25 g. sodium thiosulfate (Na:S203-5H in 1,000 ml freshly boiled, cooled, distilled water and add 0.1 g. sodium carbonate to the solution. 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 180o C. and dilute to volume in a 500-ml. volumetric flask. To a 500-ml. iodine flask, pipet 50 ml. of iodate solution. Add 2 g. potassium iodide and 10 ml. of iN 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=(W/M)x 2.80 N=Normality of stock thiosulfate solution. M=Volume of thiosulfate required, ml. W=Weight of potassium iodate, grams.


2.80=(10(conversion of g. to mg.) x 0.1

(fraction iodate used)]/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,Os) or 0.40 g. sodium sulfite (Na2SO,) 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 concentra tion 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:

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. 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 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 foil, to prevent deterioration. Determine the volume of air 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

ugSO2/ml.=((A-B) (N) (32,000)/25) (x0.02) 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). Dye Specifications. The pararosaniline dye must meet the following performance specifications: (1) The dye must 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 absor. bance unit at 22° C. with a 1-cm. optical

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