Environment is a vast and complex set, made of various elements, that is caused by the process of evolution of beings and composers of earth and thus it influences and also is influenced by human activities. Atmosphere which is the most dynamic fluid of this environment is used as a receptive of the wastes. The recent awareness of the pollution problem catches so much attention on chemical parameters of the rainwater, especially on main cations and anions and heavy metals that are important pollutants after organic pollutants and these facts cause acid rain especially in industrial countries. The level of pollution in industrial and urban areas can be determined by the chemistry of the rainwater. Nowadays the chemistry of the rainwater is considered as an indicator for controlling of the pollution in most countries. The composition of the main elements of rain depends on the content of the atmosphere and different particles that exist in the air. Sampling and analyzing of the rainwater are useful techniques for studying the chemical composition of the rainwater, understanding of different resources that contribute to rainwater chemistry and understanding of regional and local dispersion of pollutants and their potential effects on echosystems by means of the deposition process. In this research, for studying the chemistry of rainwater in Isfahan city, 6 stations were chosen in different directions. The sampling of the rainwater in these stations was done for two years in rainy seasons- from September 2007 to April 2009. The results of the analysis of rainwater showed that the pH of this region with an average of 7.34 is alkaline. It seems that the local soil and the dust particles that are in the orbit of the rainy clouds are effective in this fact. Among these 6 stations, Zarin shahr station has got the highest pH and it can be because of the highest amount of bicarbonate ions. Also considering the fact that this station is in the south-west of Isfahan and is the entrance of the rainy mass to Isfahan , it is still not influenced by the acid compounds of the rain. The lowest pH is related to the stations in the north of Isfahan , Isfahan University of technology and Second Robat Street. That is probably because of the influence of the great industries like Isfahan Refinery and Power plant which are considered as important sources of pollution.
