Page images
PDF
EPUB
[merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small]

THE

APPENDIX D-REFERENCE METHOD FOR

MEASUREMENT OF PHOTOCHEMICAL OXIDANTS
CORRECTED FOR INTERFERENCES DUE TO
NITROGEN OXIDES AND SULFUR DIOXIDE
1. Principle and Applicability.

1.1 Ambient air and ethylene are delivered simultaneously to a mixing zone where the ozone in the air reacts with the ethylene to emit light which is detected by a photomultiplier tube. The resulting photocurrent is amplified and is either read directly or displayed on a recorder.

1.2 The method is applicable to the continuous measurement of ozone in ambient air.

2. Range and Sensitivity.

2.1 The range is 9.8 ug. 03/m.3 to greater than 1960 ug. 03/m.3 (0.005 p.p.m. Og to greater than 1 p.p.m. 03).

2.2 The sensitivity is 9.8 kg. 03/m.: (0.005 p.p.m. O3).

3. Interferences.

3.1 Other oxidizing and reducing species normally found in ambient air do not interfere.

4. Precision and Accuracy.

4.1 The average deviation from the mean of repeated single measurements does not exceed 5 percent of the mean of the measurements.

4.2 The method is accurate within +7 percent.

5. Apparatus.

5.1 Detector Cell. Figure D1 is a drawing of a typical detector cell showing flow paths

of gases, the mixing zone, and placement of the photomultiplier tube. Other flow paths in which the air and ethylene streams meet at a point near the photomultiplier tube are also allowable.

5.2 Air Flowmeter. A device capable of controlling air flows between 0-1.5 1/min.

5.3 Ethylene Flowmeter. A device capable of controlling ethylene flows between 0-50 ml./min. At any flow in this range, the device should be capable of maintaining constant flow rate within +3 ml./min.

5.4 Air Inlet Filter. A Teflon filter capable of removing all particles greater than 5 microns in diameter.

5.5 Photomultiplier Tube. A high gain low dark current (not more than 1x10-9 ampere) photomultiplier tube having its maximum gain at about 430 nm. The following tubes are satisfactory: RCA 4507, RCA 8575, EMI 9750, EMI 9524, and EMI 9536.

5.6 High Voltage Power Supply. Capable of delivering up to 2,000 volts of regulated power.

5.7 Direct Current Amplifier. Capable of full scale amplication of currents from 10-10 to 10-7 ampere; an electrometer is commonly used.

5.8 Recorder. Capable of full scale display of voltages from the DC amplifier. These voltages commonly are in the 1 millivolt to 1-volt range.

5.9 Ozone Source and Dilution System. The ozone source consists of a quartz tube

an

into which ozone-free air is introduced and then irradiated with a very stable low pressure mercury lamp. The level of irradiation is controlled by an adjustable aluminum sleeve which fits around the lamp. Ozone concentrations are varied by adjustment of this sleeve. At a fixed level of irradiation, ozone is produced at a constant rate. By carefully controlling the flow of air through the quartz tube, atmospheres are generated which contain constant concentrations of ozone. The levels of ozone in the test atmospheres are determined by the neutral buffered potassium iodide method (see section 8). This ozone source and dilution system is shown schematically in Figures D2 and D3, and has been described by Hodgeson, Stevens, and Martin.

5.10 Apparatus for Calibration

5.10.1 Absorber. All-glass impingers as shown in Figure D4 are recommended. The impingers may be purchased from most major glassware suppliers. Two absorbers in series are needed to insure complete collection of the sample.

5.10.2 Air Pump. Capable of drawing 1 liter/minute through the absorbers. The pump should be equipped with a needle valve on the inlet side to regulate flow.

5.10.3 Thermometer. With accuracy of +2° C.

5.10.4 Barometer. Accurate to the nearest mm. Hg.

5.10.5 Flowmeter. Calibrated metering device for measuring flow up to 1 liter/minute within +2 percent. (For measuring flow through impingers.)

5.10.6 Flowmeter. For measuring airflow past the lamp; must be capable of measuring flows from 2 to 15 liters/minute within +5 percent.

5.10.7 Trap. Containing glass wool to protect needle valve.

5.10.8 Volumetric Flasks. 25, 100, 500, 1,000 ml.

5.10.9 Buret. 50 ml.

5.10.10 Pipets. 0.5, 1, 2, 3, 4, 10, 25, and 50 ml. volumetric.

5.10.11 Erlenmeyer Flasks. 300 ml.

5.10.12 Spectrophotometer. Capable of measuring absorbance at 352 nm. Matched 1-cm. cells should be used.

6. Reagents.
6.1 Ethylene. C. P. grade (minimum).
6.2 Cylinder Air. Dry grade.

6.3 Activated Charcoal Trap. For filtering cylinder air.

6.4 Purified Water. Used for all reagents. To distilled or deionized water in an all-glass distillation apparatus, add a crystal of potassium permanganate and a crystal of barium hydroxide, and redistill.

6.5 Absorbing Reagent. Dissolve 13.6 g. potassium dihydrogen phosphate (KH,PO.), 14.2 g. anhydrous disodium hydrogen phosphate (Na,HPO) or 35.8 g. dodecahydrate salt (Na,HPO 12H,0), and 10.0 g. potassium iodide (KI) in purified water and dilute to

1,000 ml. The pH should be 6.8+0.2. The solution is stable for several weeks, if stored in a glass-stoppered amber bottle in a cool, dark place.

6.6 Standard Arsenious Oxide Solution (0.05 N). Use primary standard grade arsenious oxide (As, 03). Dry 1 hour at 105° C. immediately before using. Accurately weigh, to the nearest 0.1 mg., 2.4 g. arsenious oxide from a small glass-stoppered weighing bottle. Dissolve in 25 ml. 1 N sodium hydroxide in a flask or beaker on & steam bath. Add 25 ml. 1 N sulfuric acid. Cool, transfer quantitatively to a 1,000-ml. volumetric flask, and dilute to volume. NOTE: Solution must be neutral to litmus, not alkaline.

wt As,Og (8.) Normality As2O3=

49.46 6.7 Starch Indicator Solution (0.2 per cent). Triturate 0.4 g. soluble starch and approximately 2 mg. mercuric iodide (preservative) with a little water. Add the paste slowly to 200 ml. of boiling water. Continue boiling until the solution is clear, allow to cool, and transfer to a glass-stoppered bottle.

6.8 Standard Iodine Solution (0.05 N).

6.8.1 Preparation. Dissolve 5.0 g. potassium iodide (KI) and 3.2 g. resublimed iodine (I,) in 10 ml. purified water. When the iodine dissolves, transfer the solution to a 500-ml. glass-stoppered volumetric flask. Dilute to mark with purified water and mix thoroughly. Keep solution in a dark brown glassstoppered bottle away from light, and restandardize as necessary.

6.8.2 Standardization. Pipet accurately 20 ml. standard arsenious oxide solution into a 300-ml. Erlenmeyer flask. Acidify slightly with 1:10 sulfuric acid, neutralize with solid sodium bicarbonate, and add about 2 g. excess. Titrate with the standard iodine solution using 5 ml, starch solution as indicator. Saturate the solution with carbon dioxide near the end point by adding 1 ml. of 1:10 sulfuric acid. Continue the titration to the first appearance of a blue color which persists for 30 seconds.

ml. As2O3 X Normality As,O3 Normality 12=

ml, 12 6.9 Diluted Standard Iodine. Immediately before use, pipet 1 ml. standard iodine solu. tion into a 100-ml. volumetric flask and dilute to volume with absorbing reagent.

7. Procedure.

7.1 Instruments can be constructed from the components given here or may be purchased. If commercial instruments are used, follow the specific instructions given in the manufacturer's manual. Calibrate the instrument as directed in section 8. Introduce samples into the system under the same conditions of pressure and flow rate as are used in calibration. By proper adjustments of zero and span controls, direct reading of ozone concentration is possible.

ers to clean 1-cm. cells. Determine the absorbance of each at 352 nm, against unexposed absorbing reagent as the reference. Add the absorbances of the two solutions to obtain total absorbance. Read total ug.Oz from the calibration curve (see 8.1). Calculate total volume of air sampled corrected to reference conditions of 25° C. and 760 mm. Hg. as follows:

P 298
VR=VX X

-X10-3

760 t+273 VR = Volume of air at reference condi

tions, m.3 V =Volume of air at sampling condi

tions, liters. P =Barometric pressure at sampling

conditions, mm. Hg. t =Temperature at sampling conditions,

°C. 10-3= Conversion of liters to m.3

Calculate ozone concentration in p.p.m. as follows:

ug. 03
p.p.m. 03=

-X 5.10 X 10-4
VR

8. Calibration.

8.1 KI Calibration Curve. Prepare a curve of absorbance of various iodine solutions against calculated ozone equivalents as follows:

8.1.1 Into a series of 25 ml. volumetric flasks, pipet 0.5, 1, 2, 3, and 4 ml. of diluted standard iodine solution (6.9). Dilute each to the mark with absorbing reagent. Mix thoroughly, and immediately read the absorbance of each at 352 nm. against unexposed absorbing reagent as the reference.

8.1.2 Calculate the concentration of the solutions as total ug. Os as follows:

Total ug. Oz=(N) (96) (V,) N=Normality I, (see 6.8.2), meq./ml. V,=Volume of diluted standard I, added,

ml. (0.5, 1, 2, 3, 4). Plot absorbance versus total ug. Og.

8.2 Instrument Calibration.

8.2.1 Generation of Test Atmospheres. Assemble the apparatus as shown in Figure D3. The ozone concentration produced by the generator can be varied by changing the position of the adjustable sleeve. For calibration of ambient air analyzers, the ozone source should be capable of producing ozone concentrations in the range 100 to 1,000 ug./m.: (0.05 to 0.5 p.p.m.) at a flow rate of at least 5 liters per minute. At all times the airflow through the generator must be greater than the total flow required by the sampling systems.

8.2.2 Sampling and Analyses of Test Atmospheres. Assemble the KI sampling train as shown in Figure D4. Use ground-glass connections upstream from the impinger. Butt-to-butt connections with Tygon tubing may be used. The manifold distributing the test atmospheres must be sampled simultaneously by the KI sampling train and the instrument to be calibrated. Check assembled systems for leaks. Record the instrument response in nanoamperes at each concentration (usually six). Establish these concentrations by analysis, using the neutral buffered potassium iodide method as follows:

8.2.2.1 Blank. With ozone lamp off, flush the system for several minutes to remove residual ozone. Pipet 10 ml. absorbing reagent into each absorber. Draw air from the ozone-generating system through the sampling train at 0.2 to 1 liter/minute for 10 minutes. Immediately transfer the exposed solution to a clean l-cm, cell. Determine the absorbance at 352 nm. against unexposed absorbing reagent as the reference. If the system blank gives an absorbance, continue flushing the ozone generation system until no absorbance is obtained.

8.2.2.2 Test Atmospheres. With the ozone lamp operating, equilibrate the system for about 10 minutes. Pipet 10 ml. of absorbing reagent into each absorber and collect samples for 10 minutes in the concentration range desired for calibration. Immediately transfer the solutions from the two absorb.

8.2.3 Instrument Calibration Curve. Instrument response from the photomultiplier tube is ordinarily in current or voltage. Plot the current, or voltage if appropriate, (y-axis) for the test atmospheres against ozone concentration as determined by the neutral buffered potassium iodide method, in p.p.m. (x-axis).

9. Calculations.

9.1 If a recorder is used which has been properly zeroed and spanned, ozone concentrations can be read directly.

9.2 If the DC amplifier is read directly, the reading must be converted to ozone concentrations using the instrument cailbration curve (8.2.3).

9.3 Conversion between p.p.m. and ug./ m.3 values for ozone can be made as follows:

ug. Os p.p.m. Os=

· X 5.10 x 10-6

m.8 10. Bibliography.

Hodgeson, J. A., Martin, B. E., and Baumgardner, R. E., “Comparison of Chemiluminescent Methods for Measurement of Atmospheric Ozone", Preprint, Eastern Analytical Symposium, New York, N.Y., October, 1970.

Hodgeson, J. A., Stevens, R. K., and Martin, B. E., “A Stable Ozone Source Applicable as a Secondary Standard for Calibration of Atmospheric Monitors”, Preprint No. 71-560, Instrument Society of America, International Conference and Exhibit, Chicago, Ili., October, 1971.

Nederbragt, G. W., Van der Horst, A., and Van Duijn, J., Nature 206, 87 (1965).

Warren, G. J., and Babcock, G., Rev. Sci. Instr. 41, 280 (1970).

[merged small][graphic][merged small][subsumed][merged small][subsumed][subsumed][subsumed][merged small][merged small][merged small][merged small][subsumed][subsumed][subsumed][subsumed][merged small][subsumed][subsumed][subsumed][merged small]

APPENDIX E-REFERENCE METHOD FOR DETER

MINATION OF HYDROCARBONS CORRECTED FOR METHANE

1. Principle and Applicability.

1.1 Measured volumes of air are delivered semicontinuously (4 to 12 times per hour) to a hydrogen flame ionization detector to measure its total hydrocarbon (THC) content. An aliquot of the same air sample is introduced into a stripper column which removes water, carbon dioxide, and hydrocarbons other than methane. Methane and carbon monoxide are passed quantitatively to a gas chromatographic column where they are separated. The methane is eluted first, and is passed unchanged through a catalytic reduction tube into the flame ionization detector. The carbon monoxide is eluted into the catalytic reduction tube where it is reduced to methane before passing through the flame ionization detector. Between analyses the stripper column is backflushed to prepare it for subsequent analysis. Hydrocarbon concentrations corrected for methane are determined by subtracting the methane value from the total hydrocarbon value.

Two modes of operation are possible: (1) A complete chromatographic analysis showing the continuous output from the detector for each sample injection; (2) The system is programed for automatic zero and span to display selected band widths of the chromatogram. The peak height is then usea as the measure of the concentration. The former operation is referred to as the chromatographic or spectro mode and the latter as the barographic or "normal" mode depending on the make of analyzer.

1.2 The method is applicable to the semicontinuous measurement of hydrocarbons corrected for methane in ambient air. The carbon monoxide measurement, which is simultaneously obtained in this method, is not required in making measurements of hydrocarbons corrected for methane and will not be dealt with here.

2. Range and Sensitivity.

2.1 Instruments are available with various range combinations. For atmospheric analysis the THC range is 0-13.1 mg./m.8 (0–20 p.p.m.) carbon (as CH.) and the methane range is 0–6.55 mg/m.: (0-10 p.p.m.). For special applications, lower ranges are available and in these applications the range for THC is 0-1.31 mg./m.3 (0-2 p.p.m.) carbon (as CH,) and for methane the range is 0-1.31 mg./m.8 (0-2 p.p.m.).

2.2 For the higher, atmospheric analysis ranges the sensitivity for THC is 0.065 mg./m.3 (0.1 p.p.m.) carbon (as CH.) and for methane the sensitivity is 0.033 mg./m.8 (0.05 p.p.m.). For the lower, special analysis ranges the sensitivity is 0.016 mg./m.8 (0.025 p.p.m.) for each gas.

3. Interferences.

3.1 No interference in the methane measurement has been observed. The THC measurement typically includes all or a portion of what is generally classified as the air peak interference. This effect is minimized by proper plumbing arrangements or is negated electronically.

4. Precision, Accuracy, and Stability.

4.1 Precision determined with calibration gases is £0.5 percent of full scale in the higher, atmospheric analysis ranges.

4.2 Accuracy is dependent on instrument linearity and absolute concentration of the calibration gases. An accuracy of 1 percent of full scale in the higher, atmospheric analysis ranges and 2 percent of full scale in the lower, special analysis ranges can be obtained.

4.3 Variations in ambient room temperature can cause changes in performance characteristics. This is due to shifts in oven temperature, flow rates, and pressure with ambient temperature change. The instrument should meet performance specifications with room temperature changes of +3° C. Baseline drift is automatically corrected in the barographic mode.

5. Apparatus.

5.1 Commercially Available THC, CH, and CO Analyzer. Instruments should be installed on location and demonstrated, preferably by the manufacturer, or his representative, to meet or exceed manufacturer's specifications and those described in this method.

5.2 Sample Introduction System. Pump, flow control valves, automatic switching valves, and flowmeter.

5.3 Filter (In-line). A binder-free, glassfiber filter with a porosity of 3 to 5 microns should be immediately downstream from the sample pump.

5.4 Stripper or Precolumn. Located outside of the oven at ambient temperature. The column should be repacked or replaced after the equivalent of 2 months of continuous operation.

5.5 Oven. For containing the analytical column and catalytic converter. The oven should be capable of maintaining an elevated temperature constant within +0.5° C. The specific temperature varies with instrument manufacturer.

6. Reagents.

6.1 Combustion Gas. Air containing less than 1.3 mg./m.3 (2 p.p.m.) hydrocarbon as methane.

6.2 Fuel. Hydrogen or a mixture of hydrogen and inert gas containing less than 0.065 mg./m.3

(0.1

p.p.m.) hydrocarbons as methane.

6.3 Carrier Gas. Hellum, nitrogen, air or hydrogen containing less than 0.065 mg./m.3 (0.1 p.p.m.) hydrocarbons as methane.

« PreviousContinue »