INTRODUCTION

It is widely agreed that in urban and suburban complexes a primary source of Lead pollution is the gasoline. Non-automotive sources of Lead in urban and suburban environments may include coal combustion, refuse and sludge incineration, burning of lead painted surfaces and certain industrial proce­sses .

In this method, lead in air-borne particulates is collected by drawing air through a filter. The filter, with collected particulates, is digested to prepare a test sample. Preparation of this sample i3 simple and rapid.. The aqueous cidic sample is scrutinised by an atomic absorption spectrophotometer at a suitable wavelength and the concentration of lead is calculated.

This method has been used in the city of Delhi over a period of two years for determination of Lead in suspended particulate matter (SPM) in ambient air at important traffic intersections.

SCOPE AND FIELD OF APPLICATION

APPLICABILITY : This method is applicable to the measurement of the concentration of airborne particulate lead found in either ambient or industrial atmospheres.

MEASUREMENT RANGE : Because airborne-particulate-Lead may constitute 1 to 5% of airborne particulate matter, analytical sensitivity is not ordinarily a problem. Based upon the f Lame mode, washed g Lass. filters and a nominal air sample volume of 2000 m3, Lead is measurable upto 0.010 ug/m3.

INTERFERENCES : No serious interferences have been reported for lead. Any possible interference due to silica from the glass fibte filters or silicates from samples can be overcome by allow­ing the acid extract to stand overnight and centrifuging at about 2000 r.p.m. for 30 minutes.

PRINCIPLE

A prepared test sample, containing the inorganic consti­tuents in aqueous acidic solution, is reduced in the f Lime furnace to the atomic state. The amount of Lead is measured by making use of its property of absorbing Light of its characteristic frequency open in in the atomic state.

REACTIONS

The most important reactions relate to the complete dissolution of the particulate sample in acidic medium to form a homogeneous test sample. As microgram quantities of material may be involved, Losses due to incomplete disdution, volati Lity, or absorption must be avoided.

REAGENTS

• Air, Compressed : In pressure Cylinders or on-Line.
• Acetylene, Compressed-: In pressure cylinders.
• G Lass Fibre Filters : Commercial Ly available 25 cm x 30 cm size, preferably Whatman EPM-2000.
• Water : Double glass distil Led.
• Nitric Acid : Analytical grade (69-71% pure)
• Standard Solution of Lead: Dissolve o .5989 of Lead nitrate and make upto one Liter with 1% nitric acid, 1 ml of this stock solution contain 1000 Ug of Lead.
• Filter Paper : Whatman 41, Circles, 11 cm., ash Less.
• spectro photometer: atomic absorption.
• Pippette : borosiLicate gLass
• valumetric fLask : borosiLicate with ground gLass stoppers, 100 ml. capacity,
• BottLes:polyethylene : screw cap, Cor storage of test samples, 100 ml, capacity.
• Beakers: borosilicate, 250 ml capacity.
• Hot Plate: electric, with temperature control
• Funnel : thistle, borosilicate,1000 diameter.

Sampling And Samples

Preparation of Laboratory Sample : Mount the glass fibre filter on a conventional high-volume or other sampler head.Draw air through the filter at a flow rate between 1.13 m3 min. and 1.60 m3/min for an appropriate period, such is 24 h.Calculate and record the total volume of air sampled, in cubic meters as the product of mean flow rate and time (APHA, 1977).

Preparation of Test Sample : Cut the exposed filter into small fragments and place in a beaker. Initiate the dissolution of the filter matrix by adding 1 ml to 2 ml of nitric acid and continue to heat gently until a few drops of nitric acid are Left. Addition of nitric acid can be repeated depending upon the filter matrix. Add 10 ml, of water. Bring nearly to the boil and filter through a Whatman 41 filter into a glass beaker. Transfer to a 100 ml, voLumetric flask. Rinse the beaker with another 10 ml, of water. Repeat the rinsing 2 to 3 times. Transfer to the 100 ml. volumetric .flask and make up test sample to the mark. Mix the contents of the volumetric flask thoroughly after adjustment to volume. Transfer the contents of the volumetric" flask to a polyethylene storage bottle. 'the test Sample is now ready for analysis. above method applies to the digestion of glass fibre filters Cellulose filters can be digested or extracted using nitric acid. Filter blank is run simultaneously with each batch ( APHA, 1977; Environment Canada, 1976).