UNIT 2Chapter 12

Environmental Chemistry

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.

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.

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

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

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

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

The Atmosphere

• Exosphere– Atmosphere merges into space in the extremely

thin exosphere– Upper limit and hottest because it is closest to the

sun

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

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

The Greenhouse Effect• The Gases – contribution – Water vapour (60%)– Carbon dioxide (26%)– Methane – Dinitrogen halogenated

fluorocarbons (HFCs)– Perfluorinated carbons

(PFCs)– Sulfur hexafluoride (SF6)

Greenhouse Gases

• Water–Higher surface temperatures cause more

water to be evaporated and the extra water vapour absorbs more heat

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

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

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

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

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

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

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

Kyoto Protocol

• The Kyoto Protocol explained

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

Acid Rain and Smog

• Rain is normally slightly acidic due to the presence of dissolved carbon dioxide, which forms carbonic acid

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

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

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.

Formation of Acid Rain

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

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

Effects of Acid Rain on Vegetation

MSN Encarta

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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

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MSN Encarta

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.

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.

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.

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)