Acid Deposition

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Acid rain Acid rain is rain that is sufficiently acidic by atmospheric pollution, that it causes environmental harm to lakes and forests It means that it possesses elevated levels of hydrogen ions (low pH). It can have harmful effects on plants, aquatic animals and infrastructure

Causes of Acid Rain Burning coal. Oil and natural gas in power stations makes electricity, giving off sulphur dioxide gas Burning petrol and oil in vehicle engines gives off nitrogen oxides as gases These gases mix with water vapour and rainwater in the atmosphere producing weak solutions of sulphuric and nitric acids – which fall as acid rain.

Process Emissions of sulfur dioxide and nitrogen oxide, which react with water molecules in the atmosphere to produce acids Nitrogen oxides can also be produced naturally by lightening strikes and sulfur dioxide is produced by volcanic eruptions

Acid Deposition Release of SO 2 and NO X by anthropogenic activities can result in acid formation, deposition SO 2 reacts in the atmosphere to form H 2 SO 4 (sulfuric acid) NO X react in the atmosphere to form HNO 3 (nitric acid) SO 2 SO 4 2- oxidation H 2 S, S 2- oxidation NO, NO 2, N 2 O oxidation NH 3 NO 3 -

Acid Rain: Fossil Fuel Burning Sulfur: Coal –Contains up to several % Sulfur as metal sulfides (e.g. FeS 2 ) –When burned, coal sulfur oxidizes to SO 2 (g) –Release of SO 2 Atmospheric H 2 SO 4 Nitrogen: Combustion –Any combustion process involving air will inadvertently fix air N 2 to form NO X Automotive exhaust Power plant emissions Forest fires

Natural rain acidity Carbonic acid Dissolution of atmospheric CO 2 into cloud droplets forms dissolved carbonic acid (H 2 CO 3 ), giving some weak acidity (clean rainwater pH ~ 5.6) CO 2 + H 2 O = H 2 CO 3 H 2 CO 3 = HCO H + (H + gives acidity)

Impact Increased amounts of nitrous oxide and sulfur dioxide in the air contribute to heart and lung problems including asthma and bronchitis Loss of fish in acidified lakes and streams Elimination of insects Loss of trees Causes paint to peel Corrosion of steel structures Erosion of stone statues

Impacts At a pH lower than 5 most fish eggs will not hatch and lower pH levels still, will kill adult fish Acid rain removes soil nutrients such as calcium and magnesium from soils Acid deposition can make snow melt more acidic

Impact of acid rain vyuw vyuw

Acid Rain Effects: Watersheds Natural buffering –Aquifer rock and surface exposed rock can naturally buffer acidity, depending on rock composition –Carbonate rock: strongly buffers pH, neutralizes acidity from rain CaCO 3 + H + = Ca 2+ + HCO 3 - (a tiny bit of limestone dissolves) Limestone rock –Will neutralize acid rain, reducing the effects of acid deposition Silicate rock –Does not react with acids as quickly, will not provide much buffering capacity, does not neutralize acid deposition

Effects of Acid Deposition: Soils Nutrient Leaching –Acids mixing into soil solutions will be neutralized, at first… –Nutrient cations (Mg 2+, Ca 2+, K +, Na +,…..) will leach from soil organic matter and minerals Cations are released into solution H + (acidity) is taken up by soil particles, organic acids in soil –Leached nutrients will be washed away in water –Long term effects: Leaching of mineral cations = starvation of soil, plants die Exhaustion of soil buffering capacity (ability to neutralize acid deposition is diminished)

Waldsterben Meaning “forest decline” –Caused by soil exhaustion through acid leaching of nutrients Slow onset Encroaches over decades Will require decades to centuries to recover Smoky Mtns in Eastern USA Eastern USA Black Forest, GermanyChina Acid rain, woods, Jizera Mountains, Czech Republic Wikipedia Image

Acidification of Lakes Like soils, lakes can buffer pH –Depends on bedrock beneath lake –Limestone bedrock has greater buffering capacity Sustained acidification can exhaust buffering capacity of lake water, surface sediments… –Lake pH drops once buffering capacity is used up –Dramatic declines in aquatic life (insects, molluscs, fish) –Requires decades to centuries to recover –Remediation Expensive, only partially effective, must be repeated Addition of lime (CaO) to lakes is a common method

Acidification of Lakes Geochemical / Ecological Effects –Aluminum toxicity Al is very insoluble at around neutral pH In low-pH lake water (<5) though, Al solubility increases Toxic: dissolved Al interferes with gill function, O 2 uptake Fish suffocate –Shelled animals At lower pH, more difficult to build chitinous shells, calcite tests Crayfish shells soften below pH ~5.1

Solutions Sulphur dioxide can be removed from power stations chimneys but this process is expensive Reduce the amount of electricity we use Use renewable energy like wind power, solar panels, tidal power, HEP schemes and geothermal energy Fit catalytic converters to vehicle exhausts which remove the nitrogen oxides Limit the number of vehicles on the roads and increase public transport

Why is acid deposition a local issue and not a global issue? – Find evidence to support this claim – Can include a map