Besides these gases, in the chemical composition of the atmosphere enter their different compounds, industrial effluents, dust, microorganisms, compounds that have suffered over time quantitative changes, same time with the development on Earth of all life forms, the development of industry rapid growth of popupatiei.
Of these, an important role plays carbon dioxide and water vapor.
The content of carbon dioxide in the atmosphere varies within 0.02 and 0.04 in volume. It comes from combustion, human breathing , the processes of decay and is consumed in the process of chlorophyll assimilation by plants in the presence of sunlight. In large urban areas, in heavily industrialized centers, near railway deposition, where the fuel is coal or diesel fuel CO2 content is over 0.04?, Compared with regions adjacent unpolluted.
Earth's atmosphere was rich in CO2 over the last century due to developing of the industries based on fossil fuels. Recent research has shown that burning fuels (coal, oil, natural gas) leads to the release of large amounts of CO2 in the atmosphere that comes from incomplete combustion.
The last time carbon dioxide has increased by 0,7-1,0 ppm / year (ppm = parts per million by volume). For the future it is estimated that this concentration will increase even more.
Polluting the atmosphere, resulting in most of from human activity, is determined by diffusion in the atmosphere of harmful substances called pollutants, solid form (powder, dust), liquid (water vapor) and gas (toxic gas) which change the natural composition of the air. It can manifest itself in the form of fog, mist, misty air. The most frequently met in urban air pollutants are carbon-dioxide gas and carbonic oxide, sulfur dioxide and sulfuric acid, various acids, dust, smoke and ash from the burning, mineral dust, hydrocarbons, microbes and viruses.
The concentration of these elements varies greatly with location, season, weather factors.
The main air pollutants can be grouped into three categories:
-Large particles whose diameter exceeds 5 and falling on the floor by their weight, they are staying only very little time in the atmosphere and are harmful especially after their fall.
-Small particles (smoke, various aerosols) with diameter less than 5 which is maintained in suspension in air, it was estimated that the particle of smoke into the air in suspension lasts 3zile, these pollutants are carcinogenic hydrocarbons.
-Gases from the combustion of fuels (sulfur oxides, nitrogen, carbon).
The main source of pollution remains the industry.