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(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. matter.

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 $ 50.7 National secondary ambient air

be exceeded more than once per year. quality standards for particulate 8 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 (a) 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 (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 ambient air quality standards for car.

potassium tetrachloromercurate (TCM). A

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 method described in Appendix C to this

pararosaniline and formaldehyde to form in

tensely colored pararosaniline methyl sulpart, or by an equivalent method, are:

fonic acid (3). The absorbance of the solu(a) 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 11 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 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 alter to protect the needle 48. 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 yg./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 call. principal 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=1081.(1/T) heavy metals by EDTA (ethylenediaminetotraacetic acid, disodium salt) and phos

6. Reagents.

6.1 Sampling. phoric acid (4, 6,). At least 60 ug. Fe (III),

6.1.1 Distilled water. Must be free from 10 ug. Mn(II), and 10 yg. Cr(III) in 10 ml.

oxidants. absorbing reagent can be tolerated in the 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. mercurio 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 approxi

mately 4.0, but it has been shown that there day. When samples are stored at 5° C. for 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 So, in solution, and the rate

The absorbing reagent is normally stable for

6 months. If a precipitate forms, discard the of decay is independent of the concentration of SOz. (7)


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

water. Prepare fresh daily. in air pollution sampling are acceptable for concentrations above 25 kg./m.: (0.01 p.p.m.).

6.2.2 Formaldehyde (0.2 percent). Duluto

5 ml. formaldehyde solution (36–38 percent) An all-glass midget impinger, as shown in Figure A1, is recommended for 30-minute and

to 1,000 ml. with distilled water. Prepare 1-hour samples.


6.2.3 Stock Iodine Solution (0.1 N). Place For 24-hour sampling, assemble an ab

12.7 g. iodine in a 250-ml. beaker; add 40 g. sorber from the following parts: Polypropylene 2-port tube closures, special

potassium iodide and 25 ml. water. Stir until

all is dissolved, then dilute to 1,000 ml, with manufacture (available from Bel-Art Prod

distilled water. ucts, Pequannock, N.J.).

6.2.4 Iodine Solution (0.01 N). Prepare Glass impingers, 6 mm. tubing, 6 inches long, one end drawn to small diameter such approximately 0.01 N iodine solution by die that 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 nut. (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 bolling 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•6H:0) in cent. For 30-minute sampling, a 22-gauge 1,000 ml. freshly bolled, 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, & 23- standardizing. To standardize, accurately gauge hypodermic needle Ave-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. lodine flask, pipet 50 ml. needle three-eighths of an inch long may be of iodate solution. Add 2 g. potassium iodide 10%(conversion of g. to mg.) X0.1 (fraction lodate used)

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

N=Normality of stock thiosulfate solu-


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 Sulfte Solution for Preparation of Working Sulfite-TCM Solution. Dissolve 0.3 g. sodium metabisulfite (Na,3,03) or 0.40 g. sodium sulfte (Na,803) in 500 ml. of recently bolled, 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 Mg./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 lodine 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. 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.

8.2.9 Working Sulfite-TCM Solution. Pipet accurately 2 ml. of the standard solution into

100 ml volumetric flask and bring to mark with 0.04 M TCM, Calculate the concentretion of sulfur dioxide in the working solution:

(A – B) (N) (32,000) ug 80g/ml.=

X 0.02

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

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

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

6.2.10 Purified Pararosaniline Stock Solu. tion (0.2 percent nominal). Dye Specifications. The pararo. saniline dye must meet the following performance specifications: (1) the dye must

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

have a wavelength of maximum absorbance
at 540 nm. 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 l-cm. optical path
length, when the blank is prepared accord-
ing 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 absorb-
ance units/ug. SO, at this path length when
the dye is pure and the sulfte solution is
properly standardized. Preparation of Stock Solution. A specially purified (99–100 percent pure) 80lution of pararosanlline, which meets the above specifications, is commercially avallable 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 & 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 elther & 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

*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 tho 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 mean. ingful corrections can be applied. I storage is necessary, refrigerate at 5° C. (see 4.2).

7.2 Analysis.

7.2.1 Sample Preparation. After collection, it & precipitate 18 observed in the sample, remove it by centrifugation. 30-Minute and 1-Hour Samples. Transfer the sample quantitatively to & 25. ml. volumetric flask; use about 5 ml. distilled water for rinsing. Delay analyses for 20 minutes to allow any ozone to decompose. 24-Hour Sample. Duluto 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 2 ml. of working sulfite-TCM solution and 8 ml. TCM solution to a 25-ml. volumetric flask. To each flask containing elther sample, control solution, or reagent blank, add 1 ml. 0.6 percent sulfamio 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 & laboratory timer that has been set for 30 minutes. Bring all flasks to volume with freshly bolled 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 A.) 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 trcell compartment of a spectrophotometer Do not allow the colored solution to sta

in the absorbance cells, beca!
may be deposited. Clean ce
after use. If the temperatur
nations does not differ by
from the callbration temr
reagent blank should be
ance unit of the y-inter
tion curve (8.2). If the r
by more than 0.03 absor"
found in the calibratior

7.2.3 Absorbance R of the sample soluti and 2.0, the sample ( & portion of the r within a few minute absorbance can be

ins the reagent blank"

*cpic readings within 10 sorbance value.

Water 8. Calibration ar

8.1 Flowineter Callbrate flowm dle (8) against

8.2 Calibrati

8.2.1 Proced curately pipet working sulfit

TO AIR as 0, 0.5, 1, 2

PUMP 25-ml. volum solution to e approximate reagents as

ontrol. précision u The temp maintaine of 20° to tion and t within 2 the tota corresp solution

TO AIR standa

PUMP the ug./.. ship

NEEDLE VALVE Bhou zero cist reg ва be


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of sulfur dioxide at levels of Interest can be prepared using permeation tubes. In the systems for generating these atmospheres, the permeation tube emits So, gas at a known, low, constant rate, provided the temperature of the tube is held constant (+0.1° C.) and provided the tube has been accurately calibrated at the temperature of use. The so, gas permeating from the tube is carried by a low flow of inert gas to a mixing chamber where it is accurately diluted with SO,-free air to the level of interest and the sample taken. These systems are shown schematically in Figures A2 and A3 and have been described in detail by O'Keeffe and Ortman (9), Scaringelli, Frey, and Saltzman (10), and Scaringelli, O'Keeffe, Rosenberg, and Bell (11). Preparation of Standard Atmospheres. Permeation tubes may be prepared or purchased. Scaringelli, O'Keeffe, Rosenberg, and Bell (11) give detailed, explicit directions for permeation tube callbration. Tubes with a certified permeation rate are available from the National Bureau of Stand. ards. Tube permeation rates from 0.2 to 0.4 ug./minute, inert gas flows of about 50 ml./ minute, and dilution air flow rates from 1.1 to 15 liters/minute conveniently give standard atmospheres containing desired levels of So, (25 to 390 mg./m.>; 0.01 to 0.15 p.p.m. SO,). The concentration of So, in any standard atmosphere can be calculated as follows:


O=Concentration of SO2, kg./m.: at ref-

erence conditions. P =Tube permeation rate, ng./minute. Ra=Flow rate of dilution air, liter/minute

at reference conditions. Ri=Flow rate of inert gas, Uter/minute at

reference conditions. Sampling and Preparation of Calibration Curve. Prepare a series (usually six) of standard atmospheres containing SO: levels from 25 to 390 ug. So,/m... Sample each atmosphere using similar apparatus and tak. ing exactly the same alr volume as will be done in atmospheric sampling. Determine absorbances as directed in 7.2. Plot the concentration of So, in ug./m.: (x-axis) against A-A, values (y-axis), draw the straight line of best fit and determine the slope. Alternatively, regression analysis by the method of least squares may be used to calculate the slope. Calculate the reciprocal of the slope and denote as Bg.

8.3 Sampling Efficiency. Collection efficiency is above 98 percent; efficiency may fall off, however, at concentrations below 25 ug./m.". (12, 13)

9. Calculations.

9.1 Conversion of Volume. Convert the volume of air sampled to the volume at rel

erence conditions of 25° C. and 760 mm. Hg. (On 24-hour samples, this may not be possible.)


298 Ve=VXX

760 t+273
VR=Volume of air at 25° C. and 760 mm.

Hg, liters.
V =Volume of air sampled, üters.
P =Barometric pressure, mm. Hg.
t =Temperature of air sample, C.
9.2 Sulfur Dioxide Concentration.

9.2.1 When sulfite solutions are used to prepare callbration curves, compute the concentration of sulfur dioxide in the sample:

(A-Ao) (109) (B.) ug. SO2/m.3=


A =Sample absorbance.
A.=Reagent blank absorbance.
10'=Conversion of Uters to cubic meters.
VR = The sample corrected to 25° C. and

760 mm. Hg, liters.
B. =Callbration factor, mg./absorbanco

D =Dilution factor.

For 30-minute and 1-hour samples,


For 24-hour samples, D=10. 9.2.2 When So, gas standard atmospheres are used to prepare calibration curves, compute the sulfur dioxide in the sample by tho following formula:

SO4, Mg./m. =(A-A) XB
A =Sample absorbance.
Ao=Reagent blank absorbance.

9.2.3 Conversion of ug./m, to p.p.m.=I desired, the concentration of sulfur dioxido may be calculated as p.p.m, SO, at reference conditions as follows:

p.p.m. 80,=ug. SO,/m..x3.82 X 10+ 10. References. (1) West, P. W., and Gaeke, G. C., "Fix&

tion of Sulfur Dioxide as Sulfitomercurate III and Subsequent Colorimetric Determination", Anal. Chem.

28, 1816 (1956). (2) Ephraims, F., “Inorganic Chemistry,"

p. 562, Edited by P.C.L. Thorne and E. R. Roberts, 5th Edition, Inter

science. (1948). (3) Lyles, G. R., Dowling, F. B., and Blanch

ard, V. J., “Quantitative Determination of Formaldehyde in Parts Per Hundred Million Concentration Lev. el", J. Air Poll. Cont. Assoc. 15, 106

(1965). (4) Scaringelli, F. P., Saltzman, B. E., and

Frey, S. A., "Spectrophotometric Determination of Atmospheric Sulfur Dioxide", Anal. Chem. 39, 1709 (1967).

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