Air pollution is a term for all physical agents (particles), chemical and biological agents that modify the natural characteristics of the atmosphere. It is difficult to define when you can talk about air pollution. In fact, the first difficulty is to clarify the boundary between pollutants and contaminants. Williamson (1973) proposed a distinction between pollutant and contaminant: a contaminant is "everything that is added to the environment that causes a deviation from the mean geochemical composition", the pollutant to be considered as such, must be responsible for a contaminant cause harmful effects to the environment, broadly construed as a union of natural and anthropogenic share. The phenomena of pollution are the result of a complex competition between factors that lead to an accumulation of the pollutants and others that instead determine their removal and their dilution into the atmosphere. The amount and terms of issue (point sources, diffuse emission height, etc..), Time of persistence of the pollutants, the degree of mixing of the air, are among the main factors that produce veriazioni space-time of the composition of the air. This is one of the main problems felt by the populations of large cities, of which there has only begun to worry about in the last 30 years. Since the 70's were in fact adopted policies for the reduction of chemical substances and many other details in the air. These policies for a greater safeguard of the environment have given of the results for some pollutants such as sulfur dioxide, lead and carbon monoxide; for others as for example nitrogen dioxide, ozone and PM10 have not brought the desired results, which has only recently discovered their critical with regard to health. The drains of the now numerous airplanes, a source of pollution that is causing increasing concern Factor or substance that causes the alteration of a stationary state through: modification of the physical parameters and / or chemical means; variation of quantitative relationships of substances already present; introduction of foreign compounds deleterious for the life directly or indirectly. The air is a heterogeneous mixture formed by gases and particles of various nature and sizes. Its composition is modified in space and time to natural causes and not, so that it is arduous to define the characteristics of quality. The inability to identify the properties of a pristine environment of reference leads to introduce the concept of conventional air pollution by establishing a standard for air quality. It is therefore considered polluted air whose composition exceeds the limits established by law in order to avoid harmful effects on humans, animals, vegetation, materials or ecosystems in general.

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