ISO 9835-1993 Ambient air determination of a black smoke index《环境空气 黑烟指数的测定》.pdf

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1、INTERNATIONAL STANDARD IS0 9835 First edition 1993-03-I 5 Ambient air - Determination of a black smoke index Air ambiant - D i.e. particles containing carbon in its elemental form. 3 Principle and theory Air is drawn through a filter paper and the reflectance of the stain produced is measured. If it

2、 is assumed that reflected light from the surface of the filter paper has passed through the layer of light absorbent par- ticles twice, reflectance from the filter surface is analogous to the absorption of light by particles sus- pended in air in accordance with the equation R=R,exp 9 ( 1 . . . (1)

3、 where R is the intensity of reflected light from the surface of a stained paper; Ro is the intensity of reflected light from the surface of a clean paper; A is the area of the stain on the filter paper, in square metres; V is the volume sampled, in cubic metres; a is the absorption coefficient, in

4、reciprocal metres. Thus, rearranging equation (1): RO a=Axln R 2v ( 1 . * . The method specified in this International Standard can be used to measure the absorption coefficient on any filter material, but the conversion of absorption coefficient or extinction coefficient to what is, by convention,

5、known as the black smoke index, is purely an arbitrary operation which is carried out by reference to tables or graphs. For further expla- nations, see annex A. 4 Apparatus 4.1 Sampling equipment. The sampler shall be designed for daily operation, or it shall be of an auto- matic type for continuous

6、 operation. Flow diagrams of alternative arrangements of sampling equipment are shown in figure 1. Details of the sampling equip- ment are given in 4.1 .I to 4.1.6. 1 IS0 9835:1993(E) 4.1.1 Air intake, a conical funnel of 30 mm to 50 mm diameter that is constructed of polyvinylchloride. The funnel s

7、hall be mounted verti- tally with the mouth downwards at a height of not less than 2.5 m and not greater than 5 m above the ground. The inlet shall be located at least 1 m hori- zontally from any external walls, 4.1.2 Connection tubing, constructed of polyvinyl- chloride, of internal diameter 8 mm f

8、 1 mm and not areater than 6 m in lenath. Bends shall be avoided if bossible but, if unavoidable, shall have a radius greater than 50 mm. b) reading the volume directly from a dry gasmeter having an accuracy of at least 5 % of the meas- ured volume (the sampling flow rate shall be 2 m3/d f 0,2 m3/d)

9、. 4.2 Reflectometer, consisting of a light source and detector and havina either an analoaue or diaital readout of either the percentage reflectance (linear scale; 0 to 100 % reflectance) or the extinction coef- ficient (logarithmic scale; 0 to infinity) type. The points on the density chart” shall

10、be within the limits shown in figure 2. 4.1.3 Filter unit. The filter holder shall be con- Instruments designed according to the requirements strutted of an electrically conducting and chemically mentioned in this subclause shall be capable of inert material (with respect to the atmosphere likely me

11、asuring the absorption coefficient with a precision to be encountered). The area of the aperture shall be 5 cm* + 5 %. The leakage across the filter and valves of better than 5 % at absorption coefficients greater than 1 x 10-5m-1. (if used) shall not exceed 2 % of the total flow rate. The filter ho

12、lder should be of a design which will pro- vide a homogeneous particle layer on the surface of the filter medium. 5 Procedure The homogeneity of the particle layer can be checked by measuring the reflectance at several points across the diameter of the stain produced by sampling par- ticles using th

13、e filter holder. The variation in reflectance across the stain shall not exceed 1 per- centage unit of reflectance. 4.1.4 Filter material. The filter membrane shall have a collection efficiency of as close to 100 % as possible in the 0,l micron to 5 micron particle size range. Variations in reflecta

14、nce across the whole sur- face area shall not exceed 1 reflectance unit. In ad- dition, the filter material shall be suitable for a flow rate of 2 m3/d. 5.1 Sampling Assemble the sampling train in the order illustrated in figure1 using the specified connection tubing (4.1,2) for all connections. Pla

15、ce a clean sheet of filter paper (4.1.4) in the filter unit. If the two faces of the paper do not have the same texture, place the paper so that the suspended particulate matter is collected on the smoother surface. Assemble the filter unit (4.1.3) according to the manufacturers instructions, Check

16、the assembled equipment for leakage. Record the initial reading of the gasmeter (if fitted). NOTE 2 The reflectance of unused filters may vary from batch to batch, and it is therefore necessary to check and adjust for the variability of the filters before use. Start the sampling pump (4.1.5), adjust

17、 the sampling rate to I,4 I/min (2 m3/d) and note the starting time. Sample for 24 h. 4.1.5 Sampling pump, capable of delivering up to 2,0 I/min of air with the filter in line. If a membrane pump is used, a 0,2 litre ballast shall be incorporated to minimize pressure fluctuations. The pump is placed

18、 before the flow or volume meter (see figure 1). At the end of the sampling period, record the flow rate and time, switch off the sampling pump and re- cord the final reading of the dry gasmeter (if fitted) and the sampling period to the nearest hour and min- ute. 4.1.6 Volume measurement and flow r

19、ate control, consisting of a sampler equipped with a flow controller capable of keeping the flow rate constant to within + 5 % of the measured flow. Measure the Calculate the volume sampled, in cubic metres, using the flow rate and the sample duration or using the readings of the dry gasmeter. (See

20、also 4.1.6.) volume sampled by either 5.2 Calibration of the reflectometer a) recording the elapsed time and calculating the volume sampled under the control of the flow controller; or Calibrate the reflectometer according to the manu- facturers instructions. 1) Kodak Publication No. Q-16. 2 IS0 983

21、5:1993(E) 1 2 3 a) Alternative 1 1 2 3 4 5 b) Alternative 2 Key 1 Air intake 2 Filter clamp 3 Sampling pump 4 Dry gasmeter 5 Flow controller 6 Variable area flowmeter 7 Elapsed time meter Figure 1 - Alternative sampling arrangements for black smoke measurement IS0 9835:1993(E) 0,7 Reflection density

22、 =$ 1 n !$ 0,6 .0,5 x c 2 d g OS4 t u 3: e -z 2 0,3 : i! on2 RO is the reflectance of the clean reference paper (100 by definition); V is the volume sampled, in cubic metres; A is the area of the stain on the filter paper, in square metres. 4 IS0 9835:1993(E) Report the absorption coefficient to the

23、 first decimal place. NOTE 3 TableA. may be used to convert the absorption coefficient, a, to the black smoke index, in line with the OECD or EEC reference methods. 6.2 Precision and accuracy The reflectance of filter stains can be read to 1 reflectance unit with 95 % confidence. The resulting confi

24、dence limits for the absorption coefficient, a, are given in table 1. Table 1 - Confidence limits for absorption coefficients Reflectance, Confidence limits R a 1) % x 1o-5 Ab %b 95 0.65 0.13 20,3 80 2,83 0,16 5,8 70 4,52 0,18 4,o 60 6,47 0,21 3,3 50 8,78 0,25 23 40 II,61 0,31 2,7 36 12.94 0.35 2.7

25、1) ForA=5,07x10-4m2andV=2m3 7 Test report The test report shall include the following information: a) a reference to this International Standard; b) a complete identification of the air sample, includ- ing date, time and location; c1 the type of filter paper and reflectometer used; d) the results ob

26、tained, including the volume sam- pled, the sample duration, the flow rate and the measured reflectance (or absorbance); e) any unusual features noted during the determi- nation; f) any operation carried out that is not specified in this International Standard; g) the location of any sources of blac

27、k smoke close to the sampler which may have contributed to the results; h) any other information relevant to the method. I IS0 9835:1993(E) Annex A (informative) Conversion of absorption coefficient to traditional black smoke units A.1 Basic theory For pure substances, the relationship between the e

28、xtent of light absorption and the depth or thickness of the absorbing material is given by Lamberts Law, which states that equal fractions of the incident radi- ation are absorbed by successive layers of equal thickness of the light absorbing substance. This is represented mathematically by the equa

29、tion I = I, exp( - al) where . . . (A.11 10 is the intensity of incident light; I is the intensity, after passage through 1 cm of the given material; a is the absorption coefficient, which is characteristic of the particular material; 1 is the thickness of the absorbing material. The absorption coef

30、ficient, a, refers to light of a par- ticular wavelength and its value varies with the wavelength of the absorbed radiation. Thus, equation (A.?) represents the transmission and absorption of monochromatic radiation in a particular medium. A.2 The theory of reflectance measurement During sampling, a

31、ir is drawn through a filter medium and the collected particles produce a stain on the surface of the filter paper. It is clear that most filter materials present a barrier to the radiation, therefore there can be no transmission of light and it is necessary to measure reflectance. Thus, to employ L

32、amberts Law (see equation A.11 it is necessary to assume that the surface of the filter material underly- ing the deposit acts as a perfect mirror and therefore the radiation passes through the absorbing layer twice. The staining power of the particulates on the surface is measured by comparing the

33、stained surface with a blank, unexposed surface. The intensity of the incident radiation, IO, and of the transmitted radiation, I, can be replaced by R. and R, assuming that the reflectance, Ro, of the unexposed filter material is analogous with the incident radiation, which is not actually measured

34、. In fact, the difference between the incident radiation and the reflected radiation is due to scatter, which can be assumed to be the same for 6 both blank and exposed filter papers and therefore ignored in terms of reflectance measurement. The thickness, 1, of the absorbing layer can be calcu- lat

35、ed using the equation lz-$ . . . (A.3 where V is the volume of air sampled, in cubic me- tres; A is the area of the stain, in square metres, on the filter medium. Thus, Lamberts Law can be adapted for reflectance measurement as follows: . . . (A.31 where a is the absorption coefficient, in reciproca

36、l metres. Thus, rearranging equation A.3: RO a=Axln R 2v ( 1 . . I (A-4) This principle makes it possible to measure reflectance under certain carefully controlled con- ditions. A.3 Reflectance and black smoke measurement The concept of black smoke has been in use for many years as a result of the “

37、standard” method published by the Organization for Economic Co-operation and Development (OECD) in 1963. A “calibration curve” was provided to convert reflectance measurements to micrograms per square centimetre of black smoke which could then be converted to a black smoke concentration. Since the r

38、elationship between reflectance and gravimetric concentration units can change from place to place and with time at any one place, it is clear that no meaningful universal relation- ship can be derived. Furthermore, the use of gravimetric units has led to considerable confusion of black smoke measur

39、ements with the results from gravimetric methods which measure the mass of suspended particulate material in a unit volume of air. IS0 9835:1993(E) A black smoke index is therefore a measure of the dirtiness or staining power of the atmosphere. The EEC Black Smoke Reference Method and the OECD metho

40、d from which it was derived employ Whatman No. 1 filter papers21 and the EEL smokestain reflectometer21. The EEL reflectometer employs white light and the efficiency of the Whatman No. 1 filter papers is quite low. Thus, the relationship between reflectance and absorption coefficient deviates from t

41、he ideal situation represented by equation A.4. The ideal situation only exists when a) monochromatic light is used; and b) the particulate material collects on the surface of the filter medium. When Whatman No. 1 filter papers are used, the par- ticles penetrate deeply into the paper and some pass

42、right through it. Under these conditions, it has been shown that equation (A.41 approximates to A RO a,=-xln - V ( 1 R . . . Thus, the theoretical absorption coefficient a (equation A.41 as determined in the standard method is related to the modified absorption coefficient 4 (equation A.51 as follow

43、s: q = 2a . . . 64.6) The conversion of the absorption coefficient to what is, by convention, known as the black smoke index, is a purely arbitrary operation which is carried out by reference to tables or graphs. The absorption coef- ficient itself is an adequate index of black smoke and conversion

44、to the traditional “black smoke concen- tration” can be carried out by reference to the cali- bration curve in figureA.l, and detailed data for the conversion is given in tableA.l. The data relate to measurements made using Whatman No. 1 filter pa- per.9) and the EEL type 43 smokestain reflectometeP

45、. Measurements may be made using other combinations of filter paper and reflectometer, but it is not possible to relate these directly to the OECD and EC data using the calibration curve in figure A.1 . 2) Whatman No. 1 filter papers and the EEL type 43 smokestain reflectometer are examples of suitable products available commercially. This information is given for the convenience of users of this International Standard and does not constitute an endorsement by IS0 of these products. 7