Chapter I-Environmental Protection Agency ating Humidity Range-The range of bient relative humidity over which the strument will meet all performance ecifications. App. F Linearity-The maximum deviation between an actual instrument reading and the reading predicted by a straight line drawn between upper and lower calibration points. dioxide concentrations of 140 ug./m.3 (0.072 p.p.m.) and 200 μg./m.3 (0.108 p.p.m.), respectively, based on an automated analysis of samples collected from a standard test atmosphere. Precision would probably be different when the analysis is performed manually. Figure E1. Typical flow diagram. APPENDIX F-REFERENCE METHOD FOR THE DETERMINATION OF NITROGEN DIOXIDE IN THE ATMOSPHERE (24-HOUR SAMPLING METHOD) 1. Principle and Applicability. 1.1 Nitrogen dioxide is collected by bubbling air through a sodium hydroxide solution to form a stable solution of sodium nitrite. The nitrite ion produced during sampling is determined colorimetrically by reacting the exposed absorbing reagent with phosphoric acid, sulfanilamide, and N-1naphthylethylenediamine dihydrochloride. 1.2 The method is applicable to collection of 24-hour samples in the field and subsequent analysis in the laboratory. 2. Range and Sensitivity. 2.1 The range of the analysis is 0.04 to 1.5 ug. NO2/ml. With 50 ml. absorbing reagent and a sampling rate of 200 ml./min. for 24 hours, the range of the method is 20-740 ug./m.3 (0.01-0.4 p.p.m.) nitrogen dioxide. 2.2 A concentration of 0.04 ug. NO2/ml. will produce an absorbance of 0.02 using 1-cm. cells. 3. Interferences. 3.1 The interference of sulfur dioxide is eliminated by converting it to sulfuric acid hydrogen peroxide before analysis. (1) cision, Accuracy, and Stability. relative standard deviations are ent and 21.5 percent at nitrogen 4.2 No accuracy data are available. 4.3 Samples are stable for at least 6 weeks. 5. Apparatus. 5.1 Sampling. See Figure F1. 5.1.1 Absorber. Polypropylene tubes 164 x 32 mm., equipped with polypropylene twoport closures.* Rubber stoppers cause high and varying blank values and should not be used. A gas dispersion tube with a fritted end of porosity B (70-100 μm. maximum pore diameter) is used. 5.1.1.1 Measurement of Maximum Pore Diameter of Frit. Carefully clean the frit with dichromate-concentrated sulfuric acid cleaning solution and rinse well with distilled water. Insert through one hole of a two-hole rubber stopper and install in a test tube containing sufficient distilled water to cover the fritted portion. Attach a vacuum source to the other hole of the rubber stopper and measure the vacuum required to draw the *Available from Bel-Art Products, Pequannock, N.J. 6.4 Zero Gas. Air containing less than 0.065 mg./m.3 (0.1 p.p.m.) total hydrocarbons as methane. 6.5 Calibration Gases. Gases needed for linearity checks (peak heights) are determined by the ranges used. Calibration gases corresponding to 10, 20, 40, and 80 percent of full scale are needed. Gases must be provided with certification or guaranteed analysis. Methane is used for both the total hydrocarbon measurement and methane measurement. 6.6 Span Gas. The calibration gas corresponding to 80 percent of full scale is used to span the instrument. 7. Procedure. 7.1 Calibrate the instrument as described in 8.1. Introduce sample into the system under the same conditions of pressure and flow rates as are used in calibration. (The pump is bypassed only when pressurized cylinder gases are used.) Figure El shows a typical flow diagram; for specific operating instructions refer to manufacturer's manual. 8. Calibration. 8.1 Calibration Curve. Determine the linearity of the system for THC and methane in the barographic mode by introducing zero gas and adjusting the respective zeroing controls to indicate a recorder reading of zero. Introduce the span gas and adjust the span control to indicate the proper value on the recorder scale. Recheck zero and span until adjustments are no longer necessary. Introduce intermediate calibration gases and plot the values obtained. If a smooth curve is not obtained, calibration gases may need replacement. 9. Calculation. 9.1 Determine concentrations of total hydrocarbons (as CH1) and CH,, directly from the calibration curves. No calculations are necessary. 9.2 Determine concentration of hydrocarbons corrected for methane by subtracting the methane concentration from the total hydrocarbon concentration. 9.3 Conversion between p.p.m. and mg./ m.3 values for total hydrocarbons (as CH1) methane and hydrocarbons corrected for methane are made as follows: p.p.m. carbon (as CH1) =[mg. carbon (as CH1)/m.3] X 1.53 10. Bibliography. Fee, G., "Multi-Parameter Air Quality Analyzer", ISA Proceedings AID/CHEMPID Symposium, Houston, Texas, April 19-21, 1971. Villalobos, R., and Chapman, R. L., “A Gas Chromatographic Method for Automatic Monitoring of Pollutants in Ambient Air", ibid. Stevens, R. K., "The Automated Gas Chromatograph as an Air Pollutant Monitor", 1970 Conference on Environmental Toxicology, U.S. Air Force, Wright-Patterson Air Force Base, Dayton, Ohio. Stevens, R. K., and O'Keeffe, A. E., Anal. Chem. 42, 143A (1970). Schuck, E. A., Altshuller, A. P., Barth, D. S. and Morgan, G. B., "Relationship of Hydrocarbons to Oxidants in Ambient Atmospheres", J. Air Poll. Cont. Assoc. 20, 297-302 (1970). Stevens, R. K., O'Keeffe, A. E., and Ortman, G. C., "A Gas Chromatographic Approach to the Semi-Continuous Monitoring of Atmospheric Carbon Monoxide and Methane”, Proceedings of 11th Conference on Methods in Air Pollution on Industrial Hygiene Studies, Berkeley, Calif., March 30-April 1, 1970. Swinnerton, J. W., Linnenbom, V. J. and Check, C. H., Environ. Sci. Technol. 3, 836 (1969). Williams, I. G., Advances in Chromatography, Giddings, J. C., and Keller, R. A., editors, Marcell Dekker, N.Y. (1968), pp. 178182. Altshuller, A. P., Kopcznski, S. L., Lonneman, W. A., Becker, T. L. and Slater, R., Environ. Sci. Technol. 1, 899 (1967). Altshuller, A. P., Cohen, I. R., and Purcell, T. C., Can. J. Chem., 44, 2973 (1966). DuBois, L., Zdrojewski, A., and Monkman, J. L., J. Air Poll. Cont. Assoc. 16, 135 (1966). Ortman, G. C., Anal. Chem. 38, 644-646 (1966). Porter, K., and Volman, D. H., Anal. Chem. 34, 748-749 (1962). Crum, W. M., Proceedings, National Analysis Instrumentation Symposium ISA, 1962. Schwink, A., Hochenberg, H., and Forderreuther, M., Brennstoff-Chemie 72, No. 9, 295 (1961). Instruction Manual for Air Quality Chromatograph Model 6800, Beckman Instrument Co., Fullerton, Calif. Instruction Manual, Bendix Corp., Ronceverte, W. Va. Instruction Manual, Byron Instrument Co., Raleigh, N.C. MSA Instruction Manual for GC Process Analyzer for Total Hydrocarbon, Methane and Carbon Monoxide, Pittsburgh, Pa. Monsanto Enviro-Chem System for Total Hydrocarbons, Methane and Carbon Monoxide Instruction Manual, Dayton, Ohio. Union Carbide Instruction Manual for Model 3020 Gas Chromatograph for COCH,-T/1, White Plains, N.Y. Instruction Manual for 350 F Analyzer, Tracor Inc., Austin, Tex. ADDENDA Figure D4. KI sampling train. B. Suggested Definitions of Performance Specifications: Range-The minimum and maximum measurement limits. Output-Electrical signal which is proportional to the measurement; intended for connection to readout or data processing devices. Usually expressed as millivolts or milliamps full scale at a given impedence. Full Scale-The maximum measuring limit for a given range. Minimum Detectable Sensitivity-The smallest amount of input concentration that can be detected as the concentration approaches zero. Accuracy-The degree of agreement between a measured value and the true value; usually expressed at percent of full scale. Lag Time-The time interval from a step change in input concentration at the instrument inlet to the first corresponding change in the instrument output. Time to 90 Percent Response-The time interval from a step change in the input concentration at the instrument inlet to a reading of 90 percent of the ultimate recorded concentration. Rise Time (90 percent)-The interval between initial response time and time to 90 percent response after a step decrease in the inlet concentration. Zero Drift-The change in instrument output over a stated time period, usually 24 hours, of unadjusted continuous operation, when the input concentration is zero; usually expressed as percent full scale. Span Drift-The change in instrument output over a stated time period, usually 24 hours, of unadjusted continuous operation, when the input concentration is a stated upscale value; usually expressed as percent full scale. Precision-The degree of agreement between repeated measurements of the same concentration. It is expressed as the average deviation of the single results from the mean. Operational Period-The period of time over which the instrument can be expected to operate unattended within specifications. Noise-Spontaneous deviations from a mean output not caused by input concentration changes. Interference-An undesired positive or negative output caused by a substance other than the one being measured. Interference Equivalent-The portion of indicated input concentration due to the presence of an interferent. Operating Temperature Range-The range of ambient temperatures over which the instrument will meet all performance specifications. |