The surface dust samples were air-dried in the laboratory just for 3 days because samples werecollected under dry weather. The samples from the same function area were then mixed together torepresent this function area. The mixed sample was separated two subsamples, one part was treated as abulk sample and sieved through a 850μm stainless sieve, and the other part was sieved for 5 min using asieve-shaker and a nest of new stainless steel sieves into six grain size fractions. The fractions sievedwere: <53 μm, 53-125 μm, 125-250 μm, 250-500 μm, 500-850 μm and >850 μm. The mass of dusts ineach size fraction was weighed and the mass proportion was calculated. Heavy metal analysis wasconducted on bulk samples and individual grain size fractions less than 850 μm in diameter. No largerfractions were analyzed because the coarser fractions carry a considerably less amount of heavy metals.The soil samples were air-dried to constant weight in laboratory. The dried samples were ground in anagate mortar acid washed and then passed through a nylon sieve with a mesh of 150 μm for furtheranalysis.
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