PROCEDURE

Analysis of test sample for the lead content is done by aspirating the test sample into the atomic absorption spectrophotometer. The instrument is set to the wavelength of maximum intensity for the 217.0 mm. line from the hollow cathode lamp. Freshly prepared standard Lead solution is aspirated before the samples for calibration of the instrument.

CALCULATIONS

The lead content of the test portion is expressed in microgram per millilitre, X1 The blank, X2, in the same units, is substracted from X1 to get the corrected concentration of lead in the test sample. Multiplication by the dilution factor, usually 100, gives the total quantity of lead in the test sample in micrograms :

NOTES ON PROCEDURE

• Collection Efficiency : For 8-h high volume sampling particulate collection efficiency of the class fibre fi lter (EPM 2000, Whatman) remains unaffected (C.B.P. & C.W.P.,1935).
• Blanks : In general, washed or unwashed high-volume filters of glass fibre are not satisfactory for trace metal analysis because of the overwhe lminc blanks. All due care a necessary to use filter media with lowest possible lead blank.
• Sampling Time : Although the method described is normally ly based upon high-volume samples taken for a 24-h sampling period, there is no reason why samples may not be taken for a shorter time period. (C.B.P. 4 C.W.P. 1985).
• Air Flow Rate : It is customary to assume, in high-volume sampling, that the decrease in air flow rate is linear and for usual purposes of calculation the mean value of initial and final flow rates is taken. This is not correct, although the error introduced by this oversimplification is not ordinarily serious. However, high volume air sampler fitted with oriface plate is preferable for accurate air flow measurement rather, than the one with water guage manometer for air flow measurement.
• Effect of Temperature and Pressure : The effect of temperature and pressure, during the sampling period, has been largely, disregarded in the past. Since these factors must have some effect on the measured air volume, it is recommended that these corrections be introduced routinely.
• For preparation of test samples, exposed surface of filter may also be cut using circular metal punch. Care should be taken to avoid contamination due to cutting edge of the punch.

REFERENCES

• APHA. 1977. Methods of air samplinq an! analysis. M.Katz (Ed.) American Public Health Association, Washington D.C.
• Central Pollution Control Board ( C.B.P. & C.W.P.), New Delhi. 1985. project report on "Impact of Autoexhaust lead pollution on Vegetation in U.T. Delhi. EIAS/1/1985-36
• Environment Canada, 1976, EPS-Air Pollution Control Directorate. Standard Reference Method for letermination of lead in air borne particulates (AAS). Report EPS 1-AP-75-4, pp. 1,11.

ACKNOWLEDGEMENT & DISCLAIMER

Authors are thankful to Central Pollution control Board for permission to present this paper. The opinions expressed are of those authors and not of the organisation they belong to.