Acid rain has been a big problem for urban area during recent decades. Acid rain comes from high concentration of air pollutant, including man made or artificial and natural, in the atmosphere. As the biggest religious town in Iran, Mashhad also imposed with this problem. In this investigation the samples of rains during autumn 2002 and spring 2003 are analyzed. The results show that concentration of different ions (SO4-2, NO2- , NO3- and NH4-) is higher than normal. Using the concentration of ions and average precipitation in Mashhad, the amount of wet deposition acid is calculated. Based on this calculation, the rate of acid that comes to the ground due to the rainfall is more than 24 Kg ha-1. Unfortunately we haven\\\'t got any critical load map for our terrain of interest to estimate the hazard. Comparing the wet deposition amount in Mashhad and North Wales in the UK shows that the wet deposition of acids in Mashhad are nearly the same as Wales that is a very pollutant area in UK. If we assume that the amount of dry deposition is something like wet deposition we can get an idea about the amount acid that comes to the ground during each year. According to the results of this research, paying more attention to Mashhad environmental affairs is recommended.

Keywords