Post on 25-Dec-2015
transcript
Acid Deposition—Ch 17
What is Acid Deposition?• Acid Deposition is the falling of acids & acid forming
compounds from the atmosphere to Earth’s surface.– SO2, NOx, and particulates can react in the atmosphere to
produce acidic chemicals that can travel long distances before deposition.
• Tall smokestacks reduce local air pollution but can increase regional air pollution.
• 66% of all SO2 & 25% of all NOx comes from electric power generation that produces energy by burning fossil fuels.
• Two Forms– Dry
• acidic gases & particles
– Wet• acid rain, fog, sleet, cloud vapor & snow
– Acid deposition is also commonly referred to acid rain (which is only one type).• Natural precipitation is slightly acidic
– pH = ~5.0-5.6
• Primarily because of acid deposition, typical rain in the US is now about 10 times more acidic
– pH = Under 5.6 & often as low as ~4.3
What is Acid Deposition?
– When gas pollutants (ex. SO2 & NO2) dissolve in rain water, various acids are formed.
• CO2 + H2O H2CO3 (carbonic acid)
• SO2 + H2O H2SO3 (sulphorous acid)
• NO2 + H2O HNO2 (nitrous acid) + HNO3 (nitric acid)
What is Acid Deposition?
Acid Rain• Forms when SO2 & NOx react with H2O vapor in air• Acidity measured using pH
– Numerical measure of the concentration of H+ ions in solution
• pH less than 7 = acidic• pH greater than 7 = alkaline or basic
– Each number represents a tenfold (10x) change
• Harmful to plants/animals• Damages structures made of limestone/marble
– Remember…• Calcite reacts w/ acid
– bubbles
Acidic Precipitation
Fossil fuelsPower plants
Industrial emissionsAuto emissions
Primary PollutantsSO2
NO2
Secondary Pollutants
H2SO4 HNO2
sulfuric acid nitric acid
soilsleaching of minerals
vegetationdirect toxicity
indirect health effects
water
sedimentsleaching aluminum
acidic precipitation
What areas are affected by acid deposition?• occurs on a regional rather than global basis.
– Serious regional problems in areas downwind from coal burning power plants, smelters, factories, & lg urban areas.
• growing problem in China, parts of the former Soviet Union, India, Nigeria, Brazil, Venezuela, & Columbia.
Health & Other Effects of Acid Deposition
• Health Effects:– respiratory diseases
• bronchitis• asthma
• Other damage:– Statues & buildings
• Especially those made of limestone or marble
– metals– car finishes
• Effects on plants:– Acid rain does not usually kill trees directly.
• can damage tree foliage by making it weaker & more susceptible to being damaged even more by other stresses
– Ex. cold temperatures, diseases, insects, drought, & fungi
• The areas hardest hit by acid deposition are mountaintop forests, which tend to have thin soils without much buffering capacity.
• Nutrient leaching from soil limits the availability of nutrients to plants
• exposure to toxic substances slowly released from the soil
Environmental Effects of Acid Deposition
• Effects on animals:– Generally, the young of most species are more sensitive to
environmental conditions than adults.– Release of metals into water
• Ex. Aluminum toxicity– Al+3 released from soil builds up in water
• Contamination of fish in some lakes with highly toxic methyl mercury.– Acid shock
• pH falls below species’ range of tolerance– Lakes and streams become acidic when the water itself and its
surrounding soil cannot buffer the acid rain enough to neutralize it.• At pH 5, most fish eggs cannot hatch. • At lower pH levels, some adult fish die.• Some acid lakes have no fish.
• How seriously vegetation & aquatic life in lakes are affected depends mostly on whether its soils are acidic or basic (…their buffering capacity).
Environmental Effects of Acid Deposition
Acid Deposition
&Aquatic Systems
• Acid deposition has not been greatly reduced– New technologies
such as scrubbers have helped
• SO2 emissions lower
• NOx emissions higher
– Effects are worse than predicted
• The Clean Air Act can’t restore ecosystems
• More must be done to control acid deposit.
Solutions
Acid Deposition
Prevention Cleanup
Reduce air pollution by improving energy efficiency
Add lime to neutralize acidified lakes
Reduce coal use
Add phosphate fertilizer to neutralize acidified lakes
Increase natural gas use
Increase use of renewable energy resources
Burn low-sulfur coal
Remove SO2 particulates & NOx from smokestack gases
Remove NOx from motor vehicular exhaust
Tax emissions of SO2