1、Designation: D3608 95 (Reapproved 2011)Standard Test Method forNitrogen Oxides (Combined) Content in the Atmosphere bythe Griess-Saltzman Reaction1This standard is issued under the fixed designation D3608; the number immediately following the designation indicates the year oforiginal adoption or, in
2、 the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the manual determination of thecombined nitrogen dioxide (N
3、O2) and nitric oxide (NO)content, total NOx; in the atmosphere in the range from 4 to10 000 g/m3(0.002 to 5 ppm (v).1.2 The maximum sampling period is 60 min at a flow rateof 0.4 L/min.1.3 The values stated in SI units are to be regarded asstandard. The values given in parentheses are for informatio
4、nonly.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Refere
5、nced Documents2.1 ASTM Standards:2D1071 Test Methods for Volumetric Measurement of Gas-eous Fuel SamplesD1193 Specification for Reagent WaterD1356 Terminology Relating to Sampling and Analysis ofAtmospheresD1357 Practice for Planning the Sampling of the AmbientAtmosphereD3195 Practice for Rotameter
6、CalibrationD3609 Practice for Calibration Techniques Using Perme-ation TubesD3631 Test Methods for Measuring Surface AtmosphericPressureE1 Specification for ASTM Liquid-in-Glass ThermometersE128 Test Method for Maximum Pore Diameter and Per-meability of Rigid Porous Filters for Laboratory Use3. Term
7、inology3.1 DefinitionsFor definitions of terms used in this testmethod, refer to Terminology D1356.4. Summary of Test Method4.1 The NO is quantitatively (1)3converted to NO2by achromic acid oxidizer. The resulting NO2, plus the NO2alreadypresent, are absorbed in an azo-dye-forming reagent (2). Ared-
8、violet color is produced within 15 min, the intensity ofwhich is measured spectrophotometrically at 550 nm.5. Significance and Use5.1 Both NO2and NO play an important role inphotochemical-smog-forming reactions. In sufficient concen-trations NO2is deleterious to health, agriculture, materials, andvi
9、sibility.5.2 In combustion processes, significant amounts of NOmay be produced by combination of atmospheric nitrogen andoxygen; at ambient temperatures, NO can be converted to NO2by oxygen and other atmospheric oxidants. Nitrogen dioxidealso may be generated from processes involving nitric acid,nit
10、rates, the use of explosives, and welding.6. Interferences6.1 Any significant interferences due to sulfur dioxide (SO2)should be negated by the oxidation step. The addition ofacetone to the reagent retards color-fading by forming atemporary addition product with SO2. This will protect thereagent fro
11、m incidental exposure to SO2and will permitreading the color intensity within 4 to 5 h (instead of the 45 minrequired without acetone) without appreciable losses.6.2 A five-fold ratio of ozone to NO2will cause a smallinterference, the maximal effect occurring in 3 h. The reagentassumes a slightly or
12、ange tint.6.3 The interferences from nitrous oxide and nitrogen pen-toxide, and other gases that might be found in polluted air areconsidered to be negligible.1This test method is under the jurisdiction of ASTM Committee D22 on AirQuality and is the direct responsibility of Subcommittee D22.03 on Am
13、bientAtmospheres and Source Emissions.Current edition approved Oct. 1, 2011. Published October 2011. Originallyapproved in 1977. Last previous edition approved in 2005 as D3608 - 95 (2005).DOI: 10.1520/D3608-95R11.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM C
14、ustomer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3The boldface numbers in parentheses refer to the list of references appended tothis test method.1Copyright ASTM International, 100 Barr Harbor Dri
15、ve, PO Box C700, West Conshohocken, PA 19428-2959, United States.7. Apparatus7.1 Sampling ProbeA glass or TFE-fluorocarbon (pre-ferred) tube, 6 to 10 mm in diameter, provided with adownward-facing intake (funnel or tip). The dead volume ofthe system should be kept minimal, to avoid loss of NOxon the
16、surfaces of the apparatus.7.2 Oxidizer TubeSoak 14 to 16-mesh firebrick or116-in.(1.5 mm molecular sieve pellets in a 17 % aqueous solution ofchromium trioxide (CrO3) for 10 to 30 min. After draining theexcess solution and drying in an oven at 105C for 30 min, thesolid oxidizer has a dull pink color
17、. This color changes to richyellow (active color) after 24-h equilibration with ambient airat 40 to 70 % relative humidity, or after drawing ambient airthrough at a flow rate of 0.5 L/min for 1 h. A change in colorto a greenish brown indicates the exhaustion of oxidizingability, and progresses with
18、a sharp boundary. Place about 3 gof the oxidizer in a 30-mL midget impinger, or fill a 5-mm tubeto a height of 80 mm and plug each end with glass wool.7.3 AbsorberAn all-glass bubbler with a 60-m maxi-mum pore diameter frit, commonly labeled “coarse,” similar tothat illustrated in Fig. 1.7.3.1 The p
19、orosity of the fritted bubbler, as well as thesampling flow rate, affect absorption efficiency. An efficiencyof over 95 % may be expected with a flow rate of 0.4 L/min orless and a maximum pore diameter of 60 m. Frits having amaximum pore diameter less than 60 m will have a higherefficiency, but wil
20、l require an inconvenient pressure drop forsampling.7.3.2 Measure the porosity of an absorber in accordancewith Test Method E128. If the frit is clogged or visiblydiscolored, carefully clean with concentrated chromic-sulfuricacid mixture, rinse well with water, and redetermine themaximum pore diamet
21、er.7.3.3 Rinse the bubbler thoroughly with water and allow todry before using.7.4 Mist Eliminator or Gas Drying Tube filled with acti-vated charcoal or soda lime is used to prevent damage to theflowmeter and pump.7.5 Air-Metering DeviceA calibrated glass variable-areaflowmeter, or dry gas meter coup
22、led with a flow indicatorcapable of accurately measuring a flow of 0.4 L/min is suitable.7.6 ThermometerASTM Thermometer 33C, meeting therequirements of Specification E1, will be suitable for mostapplications of the method.7.7 Manometer, accurate to 670 Pa (0.20 in. Hg.7.8 Air PumpA suction pump cap
23、able of drawing therequired sample flow for intervals of up to 60 min.7.9 Spectrophotometer or ColorimeterA laboratory in-strument suitable for measuring the intensity of the red-violetcolor at 550 nm, with stoppered tubes or cuvettes. Thewavelength band-width is not critical for this determination.
24、7.10 Stopwatch or Timer.8. Reagents and Materials8.1 Purity of ReagentsReagent grade chemicals shall beused in all tests.All reagents shall conform to the specificationsof the Committee on Analytical Reagents of the AmericanChemical Society, where such specifications are available.4Other grades may
25、be used, provided it is first ascertained thatthe reagent is of sufficiently high purity to permit its usewithout lessening the accuracy of the determination.8.2 Purity of WaterWater shall be deionized water inaccordance with Specification D1193 for Type I and II reagentwater. Water must be nitrite-
26、free.8.3 Absorbing ReagentDissolve5gofanhydrous sulfa-nilic acid (or 5.5 g of the monohydrate) in almost a litre ofwater containing 140 mL of glacial acetic acid. Gentle heatingis permissible to speed up the process. To the cooled mixture,add 20 mL of the 0.1 % stock solution of N-(1-naphthyl)-ethyl
27、enediamine dihydrochloride and 10-mL acetone. Dilute to1 L. The solution will be stable for several months if keptwell-stoppered in a brown bottle in the refrigerator. Theabsorbing reagent must be at room temperature before use.Avoid lengthy contact with air during both preparation and use,since abs
28、orption of nitrogen dioxide will discolor the reagent.8.4 Chromic Acid OxidantDissolve 17 g of chromiumtrioxide (CrO3) in 100 mL of water.8.5 N-(1-Naphthyl)-Ethylenediamine Dihydrochloride,Stock Solution (0.1 %)Dissolve 0.1 g of the reagent in 100mL of water. The solution will be stable for several
29、months ifkept well-stoppered in a brown bottle in the refrigerator.(Alternatively, weighed small amounts of the solid reagent maybe stored.)8.6 Sodium Nitrite (NaNO2), Standard Solution (0.0246g/L)One mL of this working solution of NaNO2produces acolor equivalent to that of 20 g of NO2in 1 L of air
30、at 101 kPa(29.92 in. Hg and 25C (see 10.2.2). Prepare fresh just before4Reagent Chemicals, American Chemical Society Specifications , AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlisted by the American Chemical Society, see Analar Standards for LaboratoryCh
31、emicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.FIG. 1 Fritted Bubbler for Sampling Combined Nitrogen OxidesD3608 95 (2011)2use by diluting from a stock solution containing 2.460 g/L ofNaNO2(ca
32、lculated as 100 %). It is desirable to assay the solidreagent (3). The stock solution is stable for 90 days at roomtemperatures, and for a year in a brown bottle under refrigera-tion.8.7 NO2Permeation DeviceSee Practice D3609.9. Sampling9.1 Sampling procedures are described in Section 11. Dif-ferent
33、 combinations of sampling rates and time may be chosento meet special needs, but sample volumes and air flow ratesmust be adjusted so that linearity is maintained betweenabsorbance and concentration over the dynamic range.9.2 See Practices D1357 for sampling guidelines.10. Calibration and Standardiz
34、ation10.1 Sampling EquipmentIf a flowmeter is used to mea-sure sample air, calibrate it prior to use using Practice D3195.If a gas meter is used, calibrate it prior to use in accordancewith Test Method D1071.10.2 Analysis:10.2.1 Recommended Procedure:10.2.1.1 Calibrated permeation tubes that contain
35、 liquefiedNO2can be used to prepare standard concentrations of NO2inair (4). See Practice D3609 for details. Analyses of theseknown concentrations give calibration curves that simulate allthe operational conditions performed during the sampling andchemical procedures. This calibration curve includes
36、 the im-portant correction for collection efficiency at various concen-trations of NO2.10.2.1.2 Prepare or obtain a TFE-fluorocarbon permeationtube that emits NO2at a rate of 0.1 to 0.2 g/min (0.05 to 0.1L/min at standard conditions of 25C and 101.3 kPa (29.92 in.Hg. Calibrate permeation tubes under
37、 a stream of dry nitrogen,using Practice D3609.10.2.1.3 To prepare standard concentrations of NO2as-semble the apparatus, as shown in Practice D3609, consistingof a water-cooled condenser; constant-temperature water bathmaintained at 20C; cylinders containing pure dry nitrogen andpure dry air, with
38、appropriate pressure regulators; needlevalves and flowmeters for the nitrogen and dry air diluent gasstreams. Bring the diluent gases to temperature by passagethrough a 2-m long copper coil immersed in the water bath.Insert a calibrated permeation tube into the central tube of thecondenser maintaine
39、d at 20C by circulating water from theconstant-temperature bath and pass a stream of nitrogen overthe tube at a fixed rate of approximately 50 mL/min. Dilute thisgas stream to the desired concentration by varying the flow rateof the “clean dry air.” This flow rate can normally be variedfrom 0.2 to 1
40、5 L/min. The flow rate of the sampling systemdetermines the lower limit for the flow rate of diluent gases.The flow rates of the nitrogen and the diluent air must bemeasured to an accuracy of 1 to 2 %. With a tube permeatingNO2at a rate of 0.1 L/min (0.19 g/min), the range ofconcentration of NO2will
41、 be between 20 to 1000 g/m3(0.01to 0.50 ppm (v), a generally satisfactory range for ambient airconditions. When higher concentrations are desired, calibrateusing longer permeation tubes.10.2.1.4 Procedure for Preparing Simulated CalibrationCurvesA multitude of curves may be prepared by selectingdiff
42、erent combinations of sampling rate and sampling time. Thefollowing description represents a typical procedure for ambi-ent air sampling of short duration. The system is designed toprovide an accurate measure of NO2in the 40 to 10 000 g/m3(0.02 to 5 ppm (v) range. It can be modified to meet specialn
43、eeds.10.2.1.5 The dynamic range of the colorimetric procedurefixes the total volume of the sample at 24 L, then to obtainlinearity between the absorbance of the solution and theconcentration of NO2in parts per million by volume, select aconstant sampling time. This fixing of sampling time is alsodes
44、irable from a practical standpoint. In this case, select asampling time of 60 min. Then, to obtain a 24-L samplerequires a flow rate of 0.4 L/min. Calculate the concentration ofstandard NO2in air as follows:C 5P1000!R 1 r(1)where:C = concentration of NO2g/m3,P = permeation rate, g/min,R = flow rate
45、of diluent air, L/min,r = flow rate of diluent nitrogen, L/min, and1000 = conversion factor to convert L to m3.10.2.1.6 A plot of the concentration of NO2in g/m3(x-axis) against absorbance of the final solution (y-axis) willyield a straight line, the inverse or the slope of which is thefactor for co
46、nversion of absorbance to g/m3. This factorincludes the correction for collection efficiency. Any deviationfrom linearity at the lower concentration range indicates achange in collection efficiency of the sampling system. Actu-ally, the standard concentration of 20 g/m3is slightly belowthe dynamic r
47、ange of the method. If this is the range of interest,the total volume of air collected should be increased to obtainsufficient color within the dynamic range of the colorimetricprocedure. Also, once the calibration factor has been estab-lished under simulated conditions, the conditions can bemodifie
48、d so that the concentration of NO2is a simple multipleof the absorbance of the colored solution.10.2.2 Alternate Procedure:10.2.2.1 Standardization is based upon the empirical obser-vation (5) that 0.82 mol of NaNO2produces the same color as1 mol of NO2. One mL of the working standard contains 24.6g
49、 of NaNO2. Since the molecular weight of NaNO2is 69.1,this is equivalent to: (24.6/69.1) 3 (46.0/0.82) = 20 g of NO2.10.2.2.2 For convenience, standard conditions are taken as101 kPa (29.92 in. Hg and 25C, at which the molar gasvolume is 24.47 L. This is very close to the standard conditionsused for air-handling equipment, 101 kPa (29.92 in. Hg,21.1C (70F, and 50 % relative humidity, at which the molargas volume is 24.76 L, or 1.2 % greater. Ordinarily, thecorrection of the sample volume to these standard conditions isslight and m
