Air

Air

Air Composition

Practise

Sacrificial Protection

Pollutants

Rusting

• Colourless and odourless
• Occupies space
• Exerts pressure
• Expansion

Barrier Methods

Sources

Catalytic Converter

Reducing emissions

Sacrificial Protection

A more reactive metal can be attached to a less reactive metal. The more reactive metal will oxidise and therefore corrode first, protecting the less reactive metal from corrosion.

There are four main types of air pollution sources: mobile sources – such as cars, buses, planes, trucks, and trains stationary sources – such as power plants, oil refineries, industrial facilities, and factories area sources – such as agricultural areas, cities, and wood burning fireplaces natural sources – such as wind-blown dust, wildfires, and volcanoes

Reducing Emissions

CO2 emissions can be reduced by using hydrogen and renewable energy supplies such as solar or wind energy instead of burning fossil fuels. Reducing the amount of livestock farming would decrease the methane emissions produced from digestion in animals. Planting more trees would remove more carbon dioxide from the atmosphere. Acid rain is caused by oxides of nitrogen and sulfur dioxide. The effects of acid rain can be reduced by decreasing the amount of oxides of nitrogen and sulfur dioxide that are produced. Catalytic convertors in vehicles can be used to remove oxides of nitrogen. Emissions of sulfur dioxide can be reduced by either:

• Using fuels which contain low levels of sulfur
• Flue gas desulfurisation - this involves reacting the sulfur dioxide emitted from burning fuels containing sulfur, with calcium oxide therefore removing it from the flue gas

Carbon monoxide Sources: incomplete combustion of fossil fuels e.g. incomplete combustion of gasoline: C8H18 + 9O2 → 5CO + 2CO2 + 9H2O Adverse effects: poisonous, combining with haemoglobin in blood and prevents it from carrying oxygen Sulfur dioxide Sources: combustion of fossil fuels containing sulfur compounds. Power stations are a major source of sulfur dioxide Adverse effects: dissolves in rain to form acid rain which causes corrosion to metal structures, buildings and statues made of carbonate rocks, damage to aquatic organisms. Pollutes crops and water supplies, irritates lungs, throats and eyes and causes respiratory problems Oxides of nitrogen Sources: reaction of nitrogen with oxygen in the presence of high temperatures, e.g. in car engines, high-temperature furnaces and when lightening occurs. It is also a product of bacterial action in soil Adverse effects: dissolves in rain to form acid rain with similar effects as SO2 as well as producing photochemical smog Compounds of lead Sources: old water pipes, old paints, petrol in some kinds of racing cars and from very old engines Adverse effects: causes significant damage to the central nervous system, young infants are particularly susceptible to lead poisoning causing brain damage.

Rusting

Corrosion is a chemical reaction. The surface of the metal will react with substances in the environment, causing it to corrode. Rusting is an example of corrosion. An example of corrosion is the rusting of iron. Iron corrodes very easily, to form iron (III) oxide. Rust flakes off the iron, exposing a new layer of iron to undergo the same process. In order for iron to rust, oxygen and water are required. Both of these can be found in the air.

Catalytic Converter

A catalytic converter is a device used to reduce the emissions from an internal combustion engine (used in most modern day automobiles and vehicles). Not enough oxygen is available to oxidize the carbon fuel in these engines completely into carbon dioxide and water; thus toxic by-products are produced. Catalytic converters are used in exhaust systems to provide a site for the oxidation and reduction of toxic by-products (like nitrogen oxides, carbon monoxide, and hydrocarbons) of fuel into less hazardous substances such as carbon dioxide, water vapor, and nitrogen gas.

Common Pollutants

Several atmospheric pollutants are produced by the combustion of hydrocarbon fuels. These include soot, carbon monoxide, sulfur dioxide and oxides of nitrogen. The carbon is released as fine black particles. We see this in smoky flames, and it is deposited as soot. Soot can cause breathing problems and it blackens buildings. It may block boilers and other appliances, or cause a fire. Carbon monoxide is a toxic gas. It is absorbed in the lungs and binds with the haemoglobin in the red blood cells. This reduces the capacity of the blood to carry oxygen. Many hydrocarbon fuels naturally contain sulfur impurities. When the fuels are burned, the sulfur oxidises to form sulfur dioxide gas. High temperatures are reached when fuels are burned in engines. At these high temperatures, nitrogen and oxygen from the air can react together to produce oxides of nitrogen. For example: nitrogen + oxygen → nitrogen monoxide N2(g) + O2(g) → 2NO(g)