1. Air Pollution

2. Consequences of Air Pollution
CO2 is a good transmitter of sunlight, but it also partially restricts infrared radiation going back from the earth into space, which produces the so-called greenhouse effect that prevents a drastic cooling of the Earth during the night
Increasing the amount of CO2 in the atmosphere reinforces this effect and is expected to result in a warming of the Earth's surface
CO2 in atmosphereGLOBAL WARMING

3. The Greenhouse Effect

4. Acid Rain
When emissions of sulfur dioxide and nitric oxide from stationary sources are transported long distances by winds, they form secondary pollutants such as nitrogen dioxide, nitric acid vapor, and droplets containing solutions of sulfuric acid, sulfate, and nitrate salts
These chemicals descend to the earth's surface in wet form as rain or snow and in dry form as a gases fog, dew, or solid particles, it is known as acid rain or acid deposition

5. Acid Rain: Its effect on a tree

6. Acid Rain
Reactions to convert to acid take place in ~2 days - travel 1000 miles
Down wind - Acid rain
Dry Dep. vs Wet Dep.
Dry Deposition
50 % of total
Can react with plants - strip nutrients
Tree dieback

8. Acid Rain and Trees

9. Forests affected by Acid Rain
Northeast US
Canada
Northern Europe
Asia

10. Acid Rain and Buildings
Many buildings are made of concrete and or stone
These compounds act as bases and react with acid
The building technically “weathers” very fast, or
Non technically “crumbles”

11. Europe
The US Capitol

12. Human Emissions - Combustion
From atm.
NOx
N2 +O2 --> 2NO
Forms in high temperatures of combustion engine
Converted in the atmosphere to HNO3 - nitric acid

13. Human Emissions - Fertilizer
N2 +Energy H+--> NH3
Formed by the Haber process
Added to fields all over the world, but often lost after harvest

14. Acid Neutralization How does this work?
Cation Exchange on clay minerals
Role of chemical weathering...

15. Where do N emissions originate?
~ 55% come from agriculture
~ 25% come from industry – e.g. coal fired power plants
~ 20% come from automobiles

16. Acid Rain Summary
Recent and current policies to reduce acid precipitation and
Nitrogen emissions are shifting the problem from one area
to another
While emissions are remaining stable or decreasing in already
Heavily impacted areas, they are increasing in formerly
“clean” or relatively unimpacted areas
(including other countries!)
Nitrogen is only one compound important in acid rain and
pollutant emissions to the atmosphere
sulfur – SOx – has been a relative success story
mercury is not an acid forming element, but is extremely
toxic and is still increasing

17. How does acid kill the fish? One way is mobilizing metals
When all base cations are striped from soils
Acid now reacts with metals e.g. aluminum
Normally aluminum is immobile
below pH 5 - mobile aluminum
Fish breath in the water
Aluminum comes out of solution
Clogs gills - suffocate

18. Smog
With the introduction of petroleum to replace coal economies in countries, photochemical smog has become predominant in many cities, which are located in sunny, warm, and dry climates with many motor vehicles
Worst episodes of photochemical smog tends to occur in summer

19. A smoggy city

20. Consequences continued
Sulfur dioxide, nitrogen oxides, ozone and peroxyacl nitrates (PANs), cause direct damage to leaves of crop plants and trees when they enter leaf pores (stomates)
Chronic exposure of leaves and needles to air pollutants can also break down the waxy coating that helps prevent excessive water loss and damage from diseases, pests, drought and frost

21. Consequences continued
"In the midwestern United States crop losses of wheat, corn, soybeans, and peanuts from damage by ozone and acid deposition amount to about $5 billion a year". (Miller 498)

22. Other types of air pollution
The difference between stratospheric and tropospheric ozone
Photochemical smog
Inversion layers

23. Where is ozone the “good guy”?
stratosphere
trophosphere

24. In the stratosphere…. Ozone blocks incoming Ultra-violet radiation
Skin cancer
Cataracts
Plant Damage

25. But, what’s happening to ozone in the Stratosphere?
Deeper purple color means
Less ozone above
Antartica

26. Why?
Chlorofluorocarbons (CFC) are very stable compounds that we produce at earth’s surface
They migrate to the stratosphere
Their chlorine gets excited by ultraviolet light
After excitation, chlorine attacks ozone layer, depleting it.

27. The Montreal Protocol has reduced use of CFC’s, but…
Their long life span means that they will be in the stratosphere for a long time, still destroying ozone.
However, the rate of increase of ozone depletion has slow, showing we are on the right track
By the way, ozone “holes” are opening up in places other than Antarctica

28. Where is ozone the “bad guy”?
stratosphere
trophosphere

29. Ozone’s bad features
Extremely reactive will burn leaves, lungs, synthetic compounds (e.g. rubbers, plastics)
Because of reactivity, is toxic in very low concentrations (parts per billion)

30. Photochemical Smog PAN = Peroxyacetyl nitrate VOCs break
Cycle, allowing
PAN to form from
NO +VOC
PAN = Peroxyacetyl nitrate

31. Examples of Smog

32. Chemical Equation for Photochemical Smog
light
NOx + VOC Ozone + Pan
reactants
products
PAN = Peroxyacetyl nitrate

33. Where reactants come from
NOx primarily from transportation
VOC from a variety of sources, including refining, other industries, etc.

34. Inversion layers trap cold air, allowing pollutants to build up in concentrations, including the compounds needed for photochemical smog
Cold air
Warm air