Sources of pollution

Air pollution can be formed through both natural and man-made processes. Some examples of these are listed below:

Natural Sources


Other natural sources are released during catastrophes such as volcanic eruptions and forest fires. Large amounts of harmful gases and smoke are released which can increase background pollution levels for years - even in areas far away from the original source. Ozone is one of the most common natural air pollutants.

Man Made Sources

Transport - Roads and Rails

Vehicles like cars, vans, buses and lorries run on petrol or diesel. When these fuels are burnt in the engine, pollutants are given out from the exhaust of the vehicles. This means road traffic is one of the biggest sources of air pollution in Wales. Near busy roads are the main pollutants are nitrogen oxides, carbon monoxide and particulate matter. Larger vehicles with bigger engines release more pollution in to the atmosphere.

Trains cause a lot less pollution than the same journey made by car. However, trains still pollute the environment. Electric trains use the electricity which is generated at power stations. When these fuels are burnt, pollutants like nitrogen oxides, sulphur dioxide and particulate matter are released into the atmosphere.


Animals like cows and sheep release a massive amount of methane through belching and breaking wind. Methane is a colourless gas which is produced in their stomachs when bacteria break down the food that they eat. Across the whole world, livestock is the biggest source of methane. Methane is the second most important greenhouse gas which can cause climate change.

Industry and Power Generation

During the Industrial Revolution in the 1800s lots of factories were built near to the large towns and cities. Today the main industrial hubs tend to be in the countryside away from cities. Nitrogen dioxide and sulphur dioxide are the main pollutants associated with industrial processes. To generate electricity fuels such as coal, gas or oil are burned at power stations. When these fuels are burnt they release nitrogen oxides, sulphur dioxide and particulate matter as well as greenhouse gases which can cause climate change.


In the UK, methane emitted from waste disposal is the largest emitter, with agriculture and livestock coming second. Methane is relased into the atmosphere when the waste that we throw away decomposes. Methane is the second most important greenhouse gas after carbon dioxide, which means that it also contributes towards climate change.

Did you know?

  • More hazardous pollutants are discharged into the air each year than are released to surface water, ground water, and land combined.
  • Urban outdoor air pollution is estimated to cause 1.3 million deaths worldwide per year.
  • Volcanic eruptions can spew massive amounts of sulphur dioxide into the atmosphere. In fact, volcanoes used to be the main source of atmospheric sulphur dioxide; today people are.