What Causes Air Pollution?

Traffic leading into Shanghai city.

Air pollution is caused by emissions from transportation, industrial factories, power plants and agriculture. The first cause is emissions from transportation.  Modern day transport such as cars, heavy duty trucks, trains, shipping vessels and airplanes all burn lots of fossil fuels to work. These fossil fuels produce both primary and secondary pollutants. The emissions from these forums of transport produce dangerous gases such as carbon monoxide, oxides of nitrogen, hydrocarbons and particulates. When these fumes mix with environmental gases they create toxic gases which cause air pollution. When this pollution is energized with sunlight you can get smog, which can hang over cities for days on end. The second cause is industrial factories and power plants. Although renewable energy is becoming more widely used in developed countries now the majority of electricity is still produced by burning fossil fuels such as coal, gas, and oil, mostly in conventional power plants. An example of this is United States where 70 percent is produced by fossil fuels. Just like transport it should theoretically produce nothing worse than carbon dioxide and water, but in practice they don't burn cleanly. Power plants produce a range of air pollutants, notably sulphur dioxide, nitrogen oxides, and particulates. They also release huge amounts of carbon dioxide, a key cause of global warming and climate change when it rises and accumulates in the atmosphere. Industrial factories that produce goods that all citizens rely on release small amounts of pollution continually over a long period of time, though the effects can accumulative. Another cause of air pollution is agriculture. Methane is a greenhouse gas which is produced when organic materials decay, or rot, and is also given off by farm animals when they digest their food.   The amount of methane gas in the atmosphere from agriculture spreading is increasing by 0.9 percent every day. This is because of the spreading agriculture industry, including the use of farm animal dung and rotting vegetation as fertilizer on crops. These are all the main cause of outdoor air pollution in civilisation today.