1. Chemistry of the Environment

2. Atmosphere Temperature varies greatly with altitude.
The profile makes a Z-shape from mesosphere to the ground.

3. Atmosphere
Pressure is highest at the surface and decreases with height.
Fluctuations in pressure are a driving force of weather.

4. Radiation
Aurora
Formed
here {
The atmosphere is the first line of defense against radiation from the Sun.

5. Composition of the Atmosphere
The composition of gases in the atmosphere is not uniform.
Lighter gases tend to rise to the top.
Near the Earth’s surface, about 99% of the atmosphere is composed of nitrogen and oxygen.
Oxygen has a much lower bond enthalpy than nitrogen, and is therefore more reactive.

6. Outer Atmosphere
The Sun emits radiation across the electromagnetic spectrum.
Light in the ultraviolet region has enough energy to break chemical bonds.
Number of photons
Wavelength, m
Energy

7. Photochemistry = Photodissociation Photoionization
Oxygen in the upper atmosphere absorbs much of the solar radiation before it reaches the lower atmosphere:
O2 + h  2 O
These bonds break homolytically.

8. Photochemistry =
Photodissociation
Photoionization
Short wavelength radiation (ionizing radiation) causes electrons to be knocked out of molecules in the upper atmosphere; very little of this radiation reaches the Earth’s surface.
The presence of these ions makes long-range radio communication possible.

9. Ozone Ozone absorbs much of the radiation between 240 and 310 nm.
It forms from reaction of molecular oxygen with the oxygen atoms produced in the upper atmosphere by photodissociation (< 242 nm).
O + O2  O3

10. Ozone Depletion
In 1974 Rowland and Molina (Nobel Prize, 1995) discovered that chlorine from chlorofluorocarbons (CFCs) may be depleting the supply of ozone in the upper atmosphere.

11. Chlorofluorocarbons (CFCs)
CFCs were used for years as aerosol propellants and refrigerants.
Mostly = CFCl3, CF2Cl2.
They are not water soluble (so they do not get washed out of the atmosphere by rain)
and are quite unreactive (so they are not degraded naturally).

12. Chlorofluorocarbons
The C—Cl bond is easily broken, though, when the molecule absorbs radiation with a wavelength between 190 and 225 nm.
The chlorine atoms formed react with ozone:
Cl + O3  ClO + O2

13. Chlorofluorocarbons
In spite of the fact that the use of CFCs in now banned in over 100 countries, ozone depletion will continue for some time because of the tremendously unreactive nature of CFCs.

14. Troposphere
Although the troposphere is made up almost entirely of nitrogen and oxygen, other gases present in relatively small amounts still have a profound effect on the troposphere.

15. Sulfur Sulfur dioxide is a by-product of the burning of coal or oil.
It reacts with moisture in the air to form sulfuric acid.
It is primarily responsible for acid rain.

16. Sulfur
High acidity in rainfall causes corrosion in building materials.
Marble and limestone (calcium carbonate) react with the acid; structures made from them erode.

17. Sulfur
SO2 can be removed by injecting powdered limestone which is converted to calcium oxide.
The CaO reacts with SO2 to form a precipitate of calcium sulfite.
Scrubbing process

18. Carbon Monoxide
Carbon monoxide binds preferentially to the iron in red blood cells.
Exposure to CO can lower O2 levels to the point of causing loss of consciousness and death.

19. Carbon Monoxide
Products that can produce carbon monoxide must contain warning labels.
Carbon monoxide is colorless and odorless, so detectors are a good idea.

20. Nitrogen Oxides
What we recognize as smog, that brownish gas that hangs above large cities like Los Angeles, is primarily nitrogen dioxide, NO2.
It forms from the oxidation of nitric oxide, NO, a component of car exhaust.

21. Photochemical Smog
Smog also contains ozone, carbon monoxide, hydrocarbons, and particles.

22. Water Vapor and Carbon Dioxide
Gases in the atmosphere form an insulating blanket that causes the Earth’s thermal consistency.
Two of the most important such gases are carbon dioxide and water vapor.

23. Water Vapor and Carbon Dioxide
This blanketing effect is known as the “greenhouse effect.”
Water vapor, with its high specific heat, is a major factor in this moderating effect.
But increasing levels of CO2 in the atmosphere is causing an increase in global temperatures.

24. Mount Pinatubo
Meelh, 2005.

25. Oceans The vast ocean contains many important compounds and minerals.
However, the ocean is a commercial source only of sodium chloride, bromine, and magnesium.

26. Desalination
“Water, water everywhere, and not a drop to drink.” Seawater has too high a concentration of NaCl for human consumption.
It can be desalinated through reverse osmosis.

27. Reverse Osmosis
Water naturally flows through a semipermeable membrane from regions of higher water concentration to regions of lower water concentration.
If pressure is applied, the water can be forced through a membrane in the opposite direction, concentrating the pure water.

28. Water Purification
Clean, safe fresh water supplies are of the utmost importance to society.
There are many steps involved in purifying water for a municipal water supply.

29. CaO and Al2(SO4)3 are added to aid in the removal of very small particles.
The water is aerated to increase the amount of dissolved oxygen and promote oxidation of organic impurities.
Ozone or chlorine is used to disinfect the water before it is sent out to consumers.