1. Acid Deposition—Ch 17

2. 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

3. What is Acid Deposition?
Acid deposition is also commonly referred to acid rain (which is only one type).
Natural precipitation is slightly acidic
pH = ~
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

4. 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)

5. 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

6. sulfuric acid nitric acid indirect health effects
Acidic Precipitation
Primary Pollutants
SO2
NO2
Secondary Pollutants
H2SO4 HNO2
sulfuric acid nitric acid
acidic precipitation
vegetation
direct toxicity
indirect health effects
water
Fossil fuels
Power plants
Industrial emissions
Auto emissions
soils
leaching of minerals
sediments
leaching aluminum

7. 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.

8. 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

9. Environmental Effects of Acid Deposition
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

10. 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).

11. Acid Deposition & Aquatic Systems

12. Acid deposition has not been greatly reduced
Solutions
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.
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
Figure 19.10
Solutions: methods for reducing acid deposition and its damage. QUESTION: Which two of these solutions do you think are the most important?
Remove NOx from motor vehicular exhaust
Tax emissions of SO2