Effect of cyclone on the composition of rainfall at Karachi City

A rapid urbanization results in increased levels of atmospheric pollutants and magnitude of this increase is much higher in the cities of developing world. Speciation of chemicals in rainwater is one way to assess the degree and nature of atmospheric contaminant accumulation and sources of these contaminants. In June 2010 an episode of heavy rain in the megacity of Karachi occurred due to the impact of Cyclone PHET, which was expected to hit Karachi city along the Arabian Sea. Cyclone impacted rainwater samples were collected from all over Karachi city and analyzed by chromatographic and spectroscopic techniques. A wide range of concentrations were observed among different sites i.e.pH (range 6.13 - 7.92, average 7.31), conductivity (range 9S/cm - 154S/cm), major anions F- (0 - 9.22eq/L), Cl- (31.7- 184.7eq/L), NO3- (2.2 - 13.7eq/L), SO42- (9.3 - 614eq/L) and cations Ca2+ (13.1 - 364.3eq/L), Mg2+ (5.83 -72.65eq/L), Na+ (49.1 - 344.7eq/L), NH4+ (0.86 - 58.59eq/L) and K + (0 - 61.44eq/L). This wide variation of distribution was attributed to the long range transportation and climatic conditions due to cyclone effect. Industrial area samples showed a dominating character of industrial influence whereas residential areas were influenced more with the coastal impact. Spatial interpolations were used to interpret the chemical data on geographical maps using ArcGIS.