UNIT 2 Chapter 12

1. UNIT 2Chapter 12 Environmental Chemistry

2. Environmental Chemistry • Study of chemical interactions in the environment and how they are affected by human activity. • Environmental chemists analyse the type (qualitative analysis) and the amount (quantitative analysis) of contaminants and other substances found in the environment. • They study both natural and artificial phenomena.

3. The Atmosphere • Earth is surrounded by regions of gases called the atmosphere • The atmosphere is divided into 5 layers (some have sub-layers) • Layers are thickest near the earth and thin out with height until it eventually merges with space.

4. The Atmosphere • Troposphere • First layer above the Earth’s surface and contains the conditions we call weather • Approx 75% of the Earth’s gases occur here • Includes the biosphere • The further from the Earth in the troposphere, the cooler the temperature

5. The Atmosphere • Stratosphere • 2nd layer of the atmosphere • Temperature increases with height because gas molecules absorb radiation from the sun • Greatest concentration of ozone – acting as a sunscreen for the Earth, absorbing ultraviolet rays • Jet aircraft fly here because it is stable

6. The Atmosphere • Mesosphere • 3rd layer • Temperature decreases as you move further away from Earth as there are less molecules to absorb radiation • Meteors burn up in the mesosphere

7. The Atmosphere • Thermosphere • The 4th layer • Temperatures very sensitive to solar activity and may vary between 500°C and 1500°C • Lower part of the thermosphere is called the ionosphere – atoms are ionised by the sun’s radiation • Auroras occur in the thermosphere

8. The Atmosphere • Exosphere • Atmosphere merges into space in the extremely thin exosphere • Upper limit and hottest because it is closest to the sun

9. Global Warming • Global warming is the rise in the average temperature of the Earth’s atmosphere. • Human activities have become a significant contributor to climate change, and this has resulted in global warming • Food crops diminish – higher temp, less rain • Changing salinity and ocean temp affect currents and marine ecosystems • Droughts more common in inland Australia – increased loss of topsoil • Floods and fires will also become more severe

10. The Greenhouse Effect • The natural rise in the Earth’s temperature caused by the presence of certain atmospheric gases • Without the greenhouse effect the Earth would be a frozen planet • Solar radiation is absorbed by the Earth and warms up the surface • The Greenhouse Effect regulates the Earth’s temperature and is absolutely essential for our survival • If excess heat is trapped, the average temperature of the Earth rises – enhanced Greenhouse Effect resulting in Global Warming

12. The Greenhouse Effect • The Gases – contribution • Water vapour (60%) • Carbon dioxide (26%) • Methane • Dinitrogen halogenated fluorocarbons (HFCs) • Perfluorinated carbons (PFCs) • Sulfur hexafluoride (SF6)

13. Greenhouse Gases • Water • Higher surface temperatures cause more water to be evaporated and the extra water vapour absorbs more heat

14. Greenhouse Gases • Carbon Dioxide • Indispensible to life as it is absorbed by plants and is an essential part of the photosynthesis process; it is produced by respiration • Remained constant for many thousands of years but we are now producing more than is being converted back to oxygen • Removing great forests from the Earth to plant crops also removes the natural carbon dioxide recycling process • Major source of CO2 is from burning fossil fuels such as coal or natural gas

15. Greenhouse Gases • Carbon Dioxide • Coal consists mainly of carbon • C(s) + O2(g) ---> CO2(g) • Natural gas consists mainly of methane • CH4(g) + 2O2(g) ---> 2H2O(l) + CO2(g) • Transportation – combustion of octane • 2C8H18(l) + 25O2 ---> 18H2O(l) + 16CO2(g) • Carbon dioxide concentrations in the atmosphere have increased by 30% over the last 200 years

16. Greenhouse Gases • Methane • Although the level of methane in the atmosphere is lower than that of carbon dioxide, its global warming capacity is 20 times greater. • Contributors • Bacteria in anaerobic conditions • Farm animals (average cow burps 280L of methane a day) • Venting natural gas deposits

17. Greenhouse Gases • Dinitrogen Oxide • Is at its highest ever recorded concentration • Breaks down slowly • Concentrations increasing due to man-made sources – land use, burning vegetation, industrial emissions • Car engines release oxides of nitrogen • Dinitrogen oxide is a far more effective greenhouse gas than carbon dioxide

18. Greenhouse Gases • Halogenated Fluorocarbons • Man-made hydrocarbons containing chlorine, fluorine and sometimes bromine • Used in aerosols, solvents and coolants • Hydrofluorocarbons (HFCs) are replacing the more damaging chlorofluorocarbons (CFCs) • Some contribute also to ozone layer depletion

19. Greenhouse Gases • Perfluorocarbons and SF6 • Almost indestructible greenhouse gases that remain in the atmosphere for over 1000 years. • Arise solely from human activity • Concentrations small but longevity a problem • SF6 is the most powerful greenhouse gas

20. Sources of greenhouse gases • Artificial sources • Electricity generation • Transport, including road, rail, air or sea with road transport being the main source (90%) • Processing, transport and storage of black coal and other fossil fuels • Industrial processes, including production of metals and other materials • Agriculture, including land clearance, rice cultivation and emissions from livestock • Decay of solid wastes in landfill, waste treatment and incineration • Land use including burning or decay of unused timber and emissions from disturbing soils • Forestry activities, including controlled burns

21. Kyoto Protocol • The Kyoto Protocol explained

22. Reducing Greenhouse Gases • Use solar power to heat water • Choose appliances with high energy ratings • Insulate houses • Walk or cycle whenever possible instead of driving • Turn off lights and appliances when they are not being used. Do not leave appliance on standby • Compost vegetable scraps • Use recyclable bags when shopping • Use rechargeable batteries • Reduce, reuse and recycle • Lobby governments to accelerate plans to decrease emissions

23. Acid Rain and Smog • Rain is normally slightly acidic due to the presence of dissolved carbon dioxide, which forms carbonic acid

24. Acid Rain • Many industrial process involve burning of coal, oil or some other fossil fuel • These fuels contain sulphur • When sulphur is burned in air it forms sulphur dioxide – SO2 • The atmosphere can cope with large quantities of SO2 if is given time to disperse the gas and break it down

25. Acid Rain • Sulphur dioxide reacts with water to become sulfurous and sulfuric acid • When it rains, the rain is no longer a mild carbonic acid solution but contains enough sulfuric acid to make it dangerous to plant and animal life. • Other gases contribute to the acid rain problem and many of these are produced by industry and by every car that uses the internal combustion engine

26. Acid Rain • Car • Spark temp causes N and O to combine and form NO • NO combines spontaneously with O to form NO2. • NO2 reacts with rainwater to form nitric acid • Carbonic acid and oxides of sulphur are largely responsible for acid rain.

27. Formation of Acid Rain

28. Harmful Effects of Acid Rain • Harmful to aquatic life • Increased acidity in water bodies • Stops eggs of certain organisms (e.g. fish) to stop hatching • Changes population ratios • Affects the ecosystem

29. Effects of Vegetation • Harmful to vegetation • Increased acidity in soil • Leaches nutrients from soil, slowing plant growth • Leaches toxins from soil, poisoning plants • Creates brown spots in leaves of trees, impeding photosynthesis • Allows organisms to infect through broken leaves

30. Effects of Acid Rain on Vegetation http://abacus.bates.edu/~ganderso/biology/bio270/clover_leaf_burns_pH2_30d.gif MSN Encarta

31. Effects of Acid Rain on Buildings and Structures • Marble is particularly susceptible • Accelerates weathering in metal and stone structures • Eg. Parthenon in Athens, Greece; Taj Mahal in Agra, India MSN Encarta http://www.lauraknauth.com/photos/france/thinker.jpg

32. Effects of Acid Rain on Human Health • Affects human health • Respiratory problems, asthma, dry coughs, headaches and throat irritations • Leaching of toxins from the soil by acid rain can be absorbed by plants and animals. When consumed, these toxins affect humans severely. • Brain damage, kidney problems, and Alzheimer's disease has been linked to people eating "toxic" animals/plants.

33. Smog • When a fire is lit and smoke is produced, small particles of carbon and other compounds are sent into the air. • When there is a lot of moisture in the air, the supply of small particles on which water droplets can condense will result in the formation of the phenomenon known as smog. • Smog is the term used for heavily polluted, moisture-laden fog.

34. Smog • A temperature inversion occurs when the air at ground level becomes colder than the air above. • The cold air at the surface is denser than the air higher up and consequently stays at the surface. This keeps the smog at ground level.

35. Review • Complete the revision questions (1 – 4) page 286 • Complete the chapter review multiple choice questions (1 – 11) • Complete the review questions (1, 2, 6, 9, 10, 11, 12,15)