Spatial variations in selected metal contents and particle size distribution in an urban and rural atmosphere of Islamabad, Pakistan

Abstract

Spatial variations in total suspended particulate matter (TSP) were investigated for distribution of metals and particle size fractions in the urban and rural atmosphere of Islamabad, Pakistan. The metals Na, K, Fe, Mn, Pb, Cd, Cr, Zn, Ni and Co, and the particle fractions <2.5, 2.5–10, 10–100 and >100 μm were included in the study. TSP samples were trapped on glass fibre filters using high volume samplers and quantification of metals was done using Atomic Absorption Spectrometry employing HNO 3 based wet digestion. At the urban site, Na was dominant at 2.384 μg/m 3 followed by K, Fe and Zn with 0.778, 0.667 and 0.567 μg/m 3 as mean concentrations, respectively. The metal levels for the rural site ranged from 0.002 μg/m 3 for Cd to 1.077 μg/m 3 for Na. However, compared with the urban site, mean Pb concentration showed an almost two-fold enhancement, i.e., 0.163 Vs. 0.327 μg/m 3. Metals and particle size source identification was done using Principal Component Analysis and Cluster Analysis. Five sources were traced out for the urban site: industrial, soil, automobile emissions, metallurgical industries and excavation activities. For the rural site, four sources were recorded: agricultural, automotive emissions, excavation activities and metallurgical units. Collectively, for both the sites, PM 10–100 emerged as a major contributor to TSP, followed by PM 2.5–10, PM <2.5 and PM >100 in that order. The metals showed in general positive relationship with fine particulate fractions (PM 2.5–10, PM <2.5), and negative correlation with coarse fractions (PM 10–100, PM >100). Comparison with the corresponding data from various Asian sites revealed that the levels of Na, K, Fe, Mn, Co and Ni for the present study were lower than those reported for grossly polluted cities of the world.