Evolution of the Atmosphere
Earth's surface originally molten, any atmosphere boiled away into space. Eventually surface cooled and thin crust formed, but volcanoes kept errupting giving out gasses including lots of carbon dioxide, water vapour, nitroden and vertually no oxygen. Oceans formed once water vapour condensed.
2 billion years later:
Green plants evolve, happy with CO atmosphere but removed CO from the air and produced O by photisynthesis. Early CO dissolve into oceans. When plants die covered by layers of sediment, locking CO that they removed from the atmosphere underground in sedimentery rocks as fossil fuels.
Oxygen builds up, kills off some early organisms that couldn't tolerate it, letting more complex organisms evolve. Vertually no CO left now.
Made up of:
Nitrogen 78% Atmosphere
also carbon dioxide (0.04%) and a little water vapour.
Formed from the remains of dead plants and animals over millions of years, then drilled/pumped out of the earth and then refined to make useful products like petrol and diesel.
Most fossil fuels are hydrocarbons - Compound of just carbon and hydrogen.
COAL is NOT a HYDROCARBON - it contains lots of impurities, but its mostly carbon.
Combustion is a type of chemical reaction. When a hydrocarbon burns, the hydrogen atoms combine with oxygen atoms from the air to make hydrogen oxide (water) and the carbon atoms combine with oxygen atoms in the air to make carbon dioxide.
When coal burns you mostly get CO .
Any reaction when oxygen is added is called an oxidation reaction, eg. combustion. Reactions when oxygen is lost are called reduction reactions.
Lots of carbon in fossil fuels, if fossil fuels are burnt they react with the oxygen in the air to produce lots of carbon dioxide which that adds to the carbon dioxide that's found naturally in the atmosphere. If when burnt there is not much oxygen available then small amounts of carbon monoxide and small particles of carbon are produced this is called incomplete burning.
Carbon Dioxide: CO an be removed from the atmosphere naturally by plants when they photosynthesise or can dissolve into rainwater, seas, lakes and rivers. Despite this CO levels can still increase if human activity adds extra CO into the atmosphere, eg. burning fossil fuels. An increase in CO level increases the greenhouse effect.
Carbon Monoxide: CO is poisonous, if a dodgy boiler in your house starts giving CO, it can make you drowsy and give you a headache, and can even kill.
Particulate Carbon: In the atmosphere they just float around and settle on the ground as soot. Soot falls on buildings making them look dirty.
Other Air Pollutants
Sulfur is found as traces in fossil fuels known as impurities. When the fuel burns so do the impurities in it (inc sulfur). When the sulfur burns it combines with the oxygen in the air to produce the primary pollutant sulfur dioxide.
Once sulfur is burned and is in the atmosphere it reacts with the moisture in the clouds to produce dilute sulfuric acid. This then falls as acid rain which causes lakes to become acidic, killing plants and animals. It also kills trees and damages buildings and statues made from some kinds of stone like limestone.
Nitrogen in the air reacts with the oxygen in the air to produce small amounts of compounds known as nitrogen oxides - nitrogen monoxide NO and nitrogen dioxide NO , this happens in car engines. Nitrogen monoxide forms when nitrogen and oxygen are exposed to a very high temperature. Once in the air it will go to react with more oxygen to produce nitrogen dioxide. Like sulfur as once in the atmosphere can become acid rain.
Simplest way is to use less electricity. The less electricity used the less fossil fuels that need to be burnt in power stations.
When coal is burned in power stations, most of the sulfur dioxide and particulates such as carbon particles and ash can be removed from the flue gasses before they are released into the atmosphere.
Sulfur can be taken out of the natural gas and fuel oil that power stations use - meaning little sulfur dioxide produced when it burns. Sulfur dioxide can be removed from flue gasses by reacting with an alkali - this is Wet scrubbing. Different types of alkali can be used:
1. Seawater: The sulfur dioxide is dissolved in seawater, producing carbon dioxide water and dissolved sulfate.
2. An alkaline slurry, eg. calcium oxide in water: The slurry is sprayed onto the gasses and the sulfur dioxide reacts with the calcium oxide producing a solid waste product, calcium sulfate.
- Efficient engines meaning burning less fuel, creating less pollution.
- Use public transport more meaning less fuel burnt overall.
- Use low-sulfur fuel, less sulfur dioxide emitted from the exhaust.
- Fitted catalytic converters which convert harmful nitrogen monoxide into harmless nitrogen and oxygen - reduction reaction. They also convert the toxic gas carbon monoxide into carbon dioxide by adding oxygen - oxidation reaction.
- A cars emissions are checked at MOT tests as there is a legal limit to the amount of polluting emissions a car can give out.
- Running cars on biofuels - renewable energy resources made from plants and waste. Meaning only carbon dioxide and water are produced.
- Powering cars with electric batteries. Electric cars produce no exhaust gasses and you just plug them into the mains to recharge them. But electricity is still made by burning fossil fuels in a power station so you are simply moving the pollution somewhere else.
Primary pollutants: When human activity adds pollutants directly to the atmosphere. Some primary pollutants are:
- Particulate Carbon (C)
- Carbon Monoxide (CO)
- Nitrogen Monoxide (NO)
- Sulfur Dioxide (SO )
- Hydrocarbons such as Methane (CH ) and Hexane (C H )
Secondary pollutants: When some primary pollutants chemically react in the air and produce other chemicals - secondary pollutants. Some secondary pollutants are:
- Nitrogen dioxide (NO )
- Ozone (O )
Slurry: A mixture of a liquid and a ground-up solid.
Range: Lowest ------ Highest measurement.