The assessment of Acid concentration and Wet deposition in Spring and Autumn Rainfalls in Mashhad.

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. mashhad, as the biggest religious town in iran, has also been imposed with this problem. in this investigation the samples of rains during autumn 2002 andspring 2003 are analyzed. the results showed 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 was calculated.based on this calculation, the rate of acid that comes to the ground due to the rainfallwas 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 theamount acid that comes to the ground during each year. according to the results of this research, paying more attention to mashhad environmental issues is recommended.