Annual and Seasonal Variations of Trace Metals in Atmospheric Suspended Particulate Matter in Islamabad, Pakistan

Total Suspended particulate matter (TSP) in urban atmosphere of Islamabad was collected using a high volume sampling technique for a period of one year. The nitric acid-perchloric acid extraction method was used and the metal contents were estimated by atomic absorption spectrophotometer. The highest mean concentration was found for Ca at 4.531 μg/m³, followed by Na (3.905 μg/m³), Fe (2.464 μg/m³), Zn (2.311 μg/m³), K (2.086 μg/m³), Mg (0.962 μg/m³), Cu (0.306 μg/m³), Sb (0.157 μg/m³), Pb (0.144 μg/m³) and Sr (0.101 μg/m³). On an average basis, the decreasing metal concentration trend was: Ca > Na > Fe > Zn > K > Mg > Cu > Sb > Pb > Sr > Mn > Co > Ni > Cr > Li > Cd [almost equal to] Ag. The TSP levels varied from a minimum of 41.8 to a maximum of 977 μg/m³, with a mean value of 164 μg/m³, which was found to be higher than WHO primary and secondary standards. The correlation study revealed very strong correlations (r > 0.71) between Fe-Mn, Sb-Co, Na-K, Mn-Mg, Pb-Cd and Sb-Sr. Among the meteorological parameters, temperature, wind speed and pan evaporation were found to be positively correlated with TSP, Ca, Fe, K, Mg, Mn and Ag, whereas, they exhibited negative relationships with relative humidity. On the other hand, Pb, Sb, Zn, Co, Cd and Li revealed significant positive correlations with relative humidity and negative with temperature, wind speed and pan evaporation. The major sources of airborne trace metals identified with the help of principle component analysis and cluster analysis were industrial emissions, automobile exhaust, biomass burning, oil combustion, fugitive emissions, resuspended soil dust and earth crust. The TSP and selected metals were also studied for seasonal variations, which showed that Na, K, Zn, Cu, Pb, Sb, Sr, Co and Cd peaked during the winter and remained lowest during the summer, while Ca, Fe, Mg and Mn were recorded highest during the spring.