Evolution of the Atmosphere
PHASE ONE: Earth's surface was orginally molten, it was so hot that any atmosphere just 'boiled away'. Things cool- thin curst formed but volcanoes kept erupting which gave out lots of gas -carbon dioxide, water vapour and nitrogen- how the atmosphere formed. Early atmosphere mostly carbon dioxide and virtually no oxygen, oceans formed when water vapour condensed.
PHASE TWO: green plants evolved over most of the Earth, happy in CO2 atmosphere, lots of CO2 then dissolved into oceans. Green plants also removed CO2 by photosynthesis, also producing O2. Plants died and buried=carbon they removed was locked up in sedimentary rocks as insoluble carbonates.
PHASE THREE: Complex organisms evolved, the build of oxygen killed some early orgamisms, but it allowed other more complex ones to evolve- very little CO2 now.
78% NITROGEN 21% OXYGEN 1% ARGON
Human activity is changing the environment- level of oxygen, nitrogen and argon is fairly constant, but H.A is adding small amounts of pollutants to the air:
carbon dioxide, carbon monoxide, particulates, sulfur dioxide, nitrogen oxides
These are realeased by many different sources, including: burning fuels in power stations and in vehicles, can be released by nature (volcanoes)
Some pollutant gases are directly harmful to humans. can cause disease and death (e.g carbon monoxide reduces amount of oxygen blood can carry) Polluntants also harm us indirectly, by damaging our environment.
- sulfur dioxide can cause acid rain, pollutes rivers and lakes- killing the fish which people catch and eat
- other pollutants lead to climate change, which brings lots of problems
Fossil fuels=hydrocarbons - formed from remains of dead plants ans animals ove rmillions of years, these fuels are drilled out of the Earth, then refined to make useful products like petrol and diesel. Only difference between fuels (petrol, diesel and fuel oil) is the size of the hydrocarbon they contain. (Coal is a bit different bc it is NOT a hydrocarbon, mainly carbon but with lots of impurities)
Burning (combustion) is a type of chemical reaction and an example of oxidation. A hydrocarbon burns, hydrogen atoms in the fuel combinew. oxygen atoms from air to make water. Carbon atoms in furl combine w. oxygen to make carbon dioxide. When coal burns you get mostly carbon dioxide.
OXIDATION REACTION: where oxygen is added REDUCTION: when oxygen is lost
Oxygen needed to burn hydrocarbons can come from the air or it can be pure, hydrocarbons burn more rapidly in pure oxygen. Pure oxygen can be obtained from the atmosphere and kept in pressurised cylinders, it can then be used. Oxygen allows the fuel to burn more rapidly so a higher temp. can be reached.
Air Pollution- carbon
- Different forms= different problems
- if fuel is burnt where there is lots of oxygen available, almost all of it ends up as CO2.
- no much O available= small amounts of carbon monoxide and small particles of carbon are produced.
- CO2, CO AND C are ALL pollutants
Carbon dioxide: an increase CO2 level increases the greenhouse effect, which is warming up the Earth. Photosynthesis removes CO2 from atmosphere
Carbon monoxide: produced in incomplete burning when there is a limited amount of oxygen. Poisonous, causes drowsiness and headaches- can kill.
Particulate carbon: escape into atmosphere, float around, eventually fall onto something and deposit themselves as soot. Make buildings look dirty.
Sulfur pollution comes from impurities in fuels, some fuels contain lots of impurities as they are extracted straight from the Earth's crust. Many of these impurities are fairly harmless but some fuels contain traces of sulfur- when fuel burns, as does sulfur. Sulfur burns with oxygen to make sulfur dioxide (SO2), so when powerstations and vehicle engines burn fossil fuels like coal and petrol, small amounts of the pollutant sulfur dioxide are produced. This ends up in our atmosphere.
Sulfur pollution causes acid rain!!!
- SO2 will stay in the atmosphere until something removes it
- usually leaves atmosphere via acid rain
- SO2 reacts with moisturein the clouds, dilute sulfuric acid is formed
- eventually, much of this acid will fall as acid rain
- acid rain causes lakes to become acidic, killing plants and animals. Also kills trees, damages buildings and statues made from kinds of stone.
Air pollution- nitrogen
- fossil fuels burn at such high temperatures that nearly atoms in the air react with each other
- nitrogen in the air reacts with oxygen in the air to produce small amounts of nitrogen oxides (nitrogen monoxide and dioxide)
- this happens in car engines
- nitrogen oxides are pollutants
NITROGEN MONOXIDE- forms when nitrogen and oxygen in the air are exposed at v high temperatures, happens in car engines.
NITROGEN DIOXIDE- once nitrogen monoxide is in the air it reacts with oxygen to produce nitrogen dioxide. Falls to ground as acid rain as it reacts with moisture in clouds, producing dilute nitric acid.
Reducing pollution from power stations- use less electricity= less fossil fuels we burn. Much of the sulfur can be taken out of natural gas and oil that power stations use, means less sulfur dioxide would be produced. When coal is burnt in power stations, most of the sulfur dioxide and particulates can be removed from the flue (chimney) gases before they're released into the atmosphere. Only way to reduce CO2 emissions is to reduce the amount of fossil fuels burnt, by using less electricity or an alternative energy source.
WET SCRUBBING: REMOVING SULFUR DIOXIDE FROM FLUE GASES BY REACTING WITH AN ALKALI. 1) Sea water used- sulfur dioxide is dissolved in it, producing carbon dioxide, water and dissolved sulfate. 2) an alkaline slurry (e.g calcium oxide in water) sprayed onto the gases and the sulfur dioxide reacts with calcium oxide. A solid waste product (calcium sulfite) is formed.
From cars: motor vehicles now have more efficient engines (less fuel and less pollution), low-sulfur fuel for cars availble, less sulfur dioxide is emitted. Many cars now have catalytic converters- convert NO to N2 and O2- reduction reaction. CC also convert toxic gas CO unto CO2 by adding oxygen. Legal limit on polluting emissions- MOT test check.
Biofuels= carbon neutral Electric batteries= pollution elsewhere