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

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 and spring 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 rainfall was 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 issues is recommended.

"The assessment of Acid concentration and Wet deposition in Spring and Autumn Rainfalls in Mashhad Abstract Acid rain has been a big problem for urban area during recent decades. Using the concentration of ions and average precipitation in Mashhad, the amount of wet deposition acid was calculated. From scientific point of view, air pollution may be defined as any atmospheric condition in which substances are present at concentrations high enough above their normal ambient levels to produce a measurable effect on, man, animals, vegetation, or materials (Reist, 1984). The concentration of pollutants emitted directly into the atmosphere (primary pollutants) and substances formed from them (secondary pollutants), and hence the pattern of acid deposition over a region, are related to the chemical processes that occur simultaneously with transport and dispersion through the atmosphere ( Blas et al 1998). As mentioned before, acidic pollutant can be deposited from the atmosphere to the earth's surface in wet and dry forms (Carruthers & Chularton, 1984). With attention to average rainfall and available ions concentrations in rain samples, amount of different ions wet deposition were calculated. Considering precipitation falls in form of snow, since wet washing coefficient of snow is more than rain, it will bring more acid to the earth surface, so we can understand the volume of destructive acids which will deposit on Mashhad field. Figures 1 and 2 show different annual ion concentration and average acidic deposition amount in Mashhad and Wales area, respectively."