Acid rain

At present human activities (industries, from automobile exhaust, burning of fossil fuels), throw into the air many tons of toxic compounds such as oxides of sulfur, nitrogen and carbon and smoke going into the atmosphere
They are the most developed countries in the North the main culprits, since launch sulfur dioxide and nitrogen dioxide to the atmosphere in the form of water vapor. Then, return to Earth in the form of acid rain or snow.

Consequences:
-Acid rain is a problem to be taken into account, since they can be transported to places where there is no burning of fuels. And also one of the consequences of air pollution and can cause many problems in life, including humans, animals, plants, soil, water and even in buildings.
-When it reach the surface there is a change in the chemical properties of soil and water. This will cause disturbances at the level of food chains, plants and forests, buildings and monuments.
-The high concentrations of nitrogen oxides in the atmosphere causing irritation of the respiratory tract affecting higher animals and man. Moreover, in the presence of ultraviolet radiation, the gas reacts with unburned hydrocarbons (released, for example, exhaust pipes.

It is important to note that there are natural sources of toxic compounds - volcanic eruptions that occur in specific in time and space while human activities tend to occur in an ongoing global and at double the quantities.