Air Section #3: Acid Precipitation

Acid Precipitation

• precipitation such as rain, sleet, or snow that contains a high concentration of acids • it is a secondary pollutant caused by the chemical reaction between water in the atmosphere & the sulfur dioxide & nitrogen oxides that are released from burning fossil fuels

Acid Precipitation

• the sulfuric acids & nitric acids that are produced will flow over & through the ground into rivers, lakes, & streams • acid precipitation can kill living organisms resulting in a decline in animal & plant populations

How Acid Precipitation Forms

pH

• a number that measures how acidic or basic a substance it • the pH scale runs from 0-14 • the lower the number, the more acidic a substance is • the higher the number, the more basic a substance it • each whole number on the scale indicates a tenfold change in acidity

pH Scale

Normal pH

• pure water has a pH of 7 which is neutral • normal precipitation is slightly acidic (~ 5.6) because CO 2 in the atmosphere forms carbonic acid • if the pH is less than 5.0, then the precipitation is considered acidic • pH varies with each geographic area

Affect on Soils & Plants

• plant communities have adapted over long periods of time to the acidity of the soil in which they grow • significant & quick changes in the acid level is called

acidification

Acidification

• changes the balance of a soil’s chemistry • an increase in the acid levels can cause some nutrients to be more easily dissolved & washed away by rainwater • can also cause aluminum & other toxic metals to be released & absorbed by plant roots • acids can also clog the stomata on plant surfaces

Acidification of a Forest

Affect on Aquatic Ecosystems

• just like plants, aquatic organisms have adapted to live within a particular pH range • even a slight increase in acid levels can lead to death

Acid Shock

• a sudden influx of acidic water that causes a rapid change in the water’s pH • this often occurs in the spring when acidic snow that accumulated in the winter melts & rushes into bodies of water

Acid Shock

• this causes large #s of fish in a population to die & affects the reproduction of fish & amphibians • organisms produce fewer eggs, most do not hatch, & those that do often have birth defects &/or cannot reproduce themselves

Fish Killed by Acid Shock

Combating Acidification

• some states in the U.S. and some countries will try to counteract the effects of acid precipitation on aquatic organisms by spraying powdered limestone on acidified lakes in the spring to help restore natural pH levels in the lake

Affect on Humans

• when soil acidity increases, toxic metals such as aluminum & mercury can be released into the environment • these toxic metals can then find their way into the human body through crops, water, & fish • this can poison the human body & even cause death at high levels

Affect on Humans

• there is also a correlation between large amounts of acid precipitation received by a community & an increase in respiratory problems by children in that community • industries (commercial fishing, logging) may struggle because of the damage from acid precipitation

Affect on Structures

• a common building material, calcium carbonate, found in concrete & limestone is dissolved by acid precipitation • some of the world’s most important & historic monuments (especially those made of marble) are slowly being eaten away

Acids Eating Rocks

International Conflict

• very hard to control because acid precipitation may form over one region or country but actually fall to the ground several kilometers away • for example, most of the acid precipitation that falls in Canada was actually produced in OH, IN, PA, IL, MO, WV, and TN

Global Problems

International Cooperation

• Canada & the U.S. signed an Air Quality Agreement in 1991 where both countries agreed to reduce acidic emissions that flow across the Canada-U.S. border • more agreements will have to be formed in the future to fight the acid precipitation problem

Question?

• Should the country that releases significant amounts of pollutants into the air that falls as acid precipitation in another country be expected to pay some of the cost of clean-up? Why or why not?