Air pollution...

There are many elements in the air that can deplete or damage the health of plants and animals (including humans). It arises from both natural processes and human activities. Elements that are not found naturally in air or with more concentration or different elements from general are called pollutants.

Pollutants can be classified as primary or secondary. Primary pollutants are those elements that have been directly emitted from a process such as ash from volcanic eruption, carbon monoxide gas by motor vehicle, sulfur dioxide gas emitting from factories.

Secondary pollutants are not directly emitted. Rather, when primary pollutants react or react when they are formed in the air. An important example of secondary pollutants is ground level ozone - one of many secondary pollutants, which forms light-chemical fog.

Keep in mind that some pollutants may be both primary and secondary, that is, they can be emitted directly and can be formed from other primary pollutants.

Major primary pollutants produced by human activities include:

Sulfur oxide (SOx) is excreted exclusively with burning of coal and oil, especially sulfur dioxide. Nitrogen oxides (NOx) are excreted especially with nitrogen dioxide by combustion at high temperatures. In the Plume cities, a mist of low air or brown can be seen as above.
Carbon oxide is the color, the odor is poisonous. Natural gas, coal or wood, is caused by incomplete burning of fuel. Vehicular emissions are a major source of carbon oxide.