POLLUTION MANAGEMENT 5.8 Acid Deposition

Assessment Statements  Outline the chemistry leading to the formation of acidified precipitation.  Describe three possible effects of acid deposition on soil, water, and living organisms.  Explain why the effect of acid deposition is regional rather than global.  Describe and evaluate pollution management strategies for acid deposition.

5.8.1 Outline the chemistry leading to the formation of acidified precipitation.  Sulfur Dioxide and nitrogen oxides are emitted from industrial complexes, vehicles, and urban areas. The longer they remain in the air, the more likely they are to react with hydrogen to produce Sulfuric (H 2 SO 4 ) and Nitric (HNO 3 ) acid.  These acids dissolve in cold droplets (rain, snow, mist, hail) and reach the ground as wet deposition. Wet deposition can be carried thousands of kilometers downwind from the source.

5.8.1 Outline the chemistry leading to the formation of acidified precipitation.  The dissolved acids consist of sulfate (SO 4 2- ), nitrate (NO 3 - ), and hydrogen (H + ) ions. These acids form acid rain. Transport of pollutants over 500 km is most likely to produce strong acid rain. Used to be local, but super smoke stacks have made it regional.  Rain water is normally a weak carbonic acid with a pH of 5.5. Acid rain is a more acidic substance due to the addition of sulfur dioxide and the oxides of nitrogen. Any rain with a pH below 5.5 is termed “acid rain”.

5.8.2 Describe three possible effects of acid deposition on soil, water, and living organisms.  Acid rain eats away at the structures, and sculptures.  Acid rain can lead to acidified lakes which are characterized by:  An impoverished species structure  Visibility several times greater than normal  White moss spreading across the bottom of the lake  Increased levels of dissolved heavy metals (cadmium, copper, etc.) which then become more easily available to plants and animals.

5.8.2 Describe three possible effects of acid deposition on soil, water, and living organisms.  The most important health effect of acid water is the result of its ability to flush trace metals from soils and pipes. This can lead to greatly concentrated groundwater and such. Acidified soil can also lead to rapid tree growth, which can be blown over.  It can severely affect trees as well. It breaks down lipids in the foliage and damages membranes. Sulfur dioxide interferes with photosynthesis. Coniferous trees only keep their needles for 2 to 3 years, instead of up to 7 years. If it loses too many, it can die.

5.8.3 Explain why the effect of acid deposition is regional rather than global.  Acidification is largely due to human activity. In addition there are a number of natural sources like bog moss, heathers, and conifers produce acid. Volcanoes also produce sulfur dioxide and nitrogen dioxide which also produce acid precipitation.  Many countries produce pollutants and they may be deposited many hundreds of kilometers from their point of origin. However this is the extent of the reach, so you won’t really see them past that.

5.8.3 Explain why the effect of acid deposition is regional rather than global.  In addition some areas have natural resources that will either help to neutralize or amplify the acid deposition.  High amount of chalk or limestone are very alkaline and can neutralize acids effectively  However much of the underlying rock of Scandinavia, Scotland, and northern Canada are granite. It is naturally acidic, and have a very low buffering capacity. Acid rain is going to cause the most damage in these regions.

5.8.4 Describe and evaluate pollution management strategies for acid deposition.  Prevention methods include the following:  Burn less fossil fuels (legislation)  Reduce the number of cars on the road, and increase the number of people using public transit  Switch to low sulfur fuel (Oil plus high grade coal)  Remove sulfur before combustion (Cheap for oil, not coal)  Reduce sulfur oxides released on combustion (FBT = Fluidized bed Technology is expensive)

5.8.4 Describe and evaluate pollution management strategies for acid deposition.  Burn coal in the presence of crushed limestone in order to reduce the acidification process  Remove sulfur from waste gases after combustion (FGD = Flue-gas desulfurization is expensive, but well-developed with a number of different methods.)  Allow decomposition of plants to return nutrients to the soil  Repairing the damage consists of adding limestone to the water to help neutralize it, however this is not really sustainable.