The main sources of pollution are:
-> Volcano eruptions
-> Natural fires
-> Dust storms
-> Housekeeping activities
The main polluter in the world is nowadays the industry. During the industrial process, harmful substances are set free into the atmosphere, causing local catastrophes when special filters are inexistent for purging the residual gases. Depending on the height of the furnaces and on the atmospheric conditions, the gases can spread locally or at big distances. All these gases will finally end up on the soil, and studies have proven the fact that up to 40 km of soil around the metallurgic works are affected by the gases these works produce.
Transports are another source of pollution. In
USA 60% of the gas pollution is caused by auto vehicles and in certain city like LA or Chicago the percentage is raised to 90%. The combustion engine is the main responsible for all this pollution. The vehicles are eliminating gases very near to the earth, leading to high concentrations of gas in the atmosphere, even for low density gases. The volume, nature and concentration of the car pollutants are depending on the type of vehicle, the nature of fuel and the cars technical conditions of functioning. Some of these pollutant substances are: particles in suspension, sulphur dioxide, lead, methane, benzene, and asbestos. All these substances are creating the smog.
Volcano eruptions are also harmful to nature as they generate liquid and solid gas products which not only harm the surrounding relief but also the atmospheres purity. A volcano eruption will form thick clouds made of dust, ash and water vapors. These suspensions can remain in the atmosphere up to 2 years. The powder that comes from volcano eruptions is considered to contribute to the green house effect created by increased CO2 concentration in the atmosphere.
Natural fires are a source of smoke and ash and happen when climate humidity lowers below the natural crisis level. This phenomenon is mostly found in the tropical areas but can also appear in US during the droughty years.
The housekeeping activities are contributing to the pollution in different ways and we dont even realize it. For warming a house some people depend on wood and so, every year millions of trees are being cut down and used as firewood.