2.3 Extraction Procedure and AnalysisTSP mass was determined gravimetrically prior to analysis ( Method IO-2.1 1999) For the metal estimation,each filter was extracted by nitric acid (Merck Suprapure 65%) and perchloric acid (Merck Suprapure 70%) mixture (10;1,v/v) (NIOSH Method-7300 1984). the extracted solution was filtered with washing by doubly distilled water and refrigerated in pre-cleaned strong polyethylene bottle until analysed (Gonzalez et al.1997) Filter andreagent blanks were also processed following the above procedure for sample treatment .Metals were determined by Atomic Absorption Spectrophotometer (Shimadzu,model AA-670,Japan) following Method IO-3.2 (1999).The metals estimated in blanks were <10% of the sample average metal contents . The accuracy of the method was evaluted using a standard reference material(OL-96) obtained from National Institute of Health (NIH),Islamabad, whwre inter-laboratory comparison of the data was also exercised .Normally/a maximum of+_5% deviation was observed in the results of the two laboratories. the results obtained were comparable within +-2% in the standard reference material used. the meteorological parameters reflecting the prevailing atmospheric conditions were recorded at Pakistan Agricultural Research Council(PARC),Islamabad
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