Air is a heterogeneous mixture made up of gases and particles of various kinds and sizes. Its composition changes in space and time due to natural causes, so that it is difficult to define its quality characteristics. The impossibility of identifying the properties of an uncontaminated reference environment leads to the introduction of the concept of atmospheric pollution by establishing a conventional standard for air quality.
Air is therefore considered polluted if its composition exceeds the limits established by law in order to avoid harmful effects on humans, animals, vegetation, materials or ecosystems in general. The effects on human health due to poor air quality mainly involve the respiratory system and the cardiovascular system.
Individual reactions to air pollution depend on the type of pollutant a person is exposed to, the degree of exposure, the individual's health and genetics. Indoor air pollution and poor urban air quality are listed as two of the worst toxic pollution problems in the world in the 2008 report.
Outdoor air pollution causes 2.1 to 4.21 million deaths every year. Overall, air pollution causes the deaths of approximately 7 million people worldwide each year and is the single largest environmental health risk in the world.
The main causes are mainly anthropogenic in this era
Emissions from vehicle traffic depend on the type of fuel, the type of vehicle and its age. All thermal engines produce water, if powered by fossil fuels they produce carbon dioxide (CO2), diesel powered vehicles mainly emit particulate matter such as PM10 and below, hydrocarbons (HC), nitrogen oxides (NOx) and sulfur dioxide (SO2) .
A petrol vehicle emits particulate matter, NOx and CO, while methane and LPG vehicles emit NOx, ultrafine particulate matter and low hydrocarbons.
In recent years, attempts have been made to adopt a logic of reducing vehicle emissions also with the introduction of the 1,2,3 euro bands etc.
and placing mandatory the catalytic converter and the particulate filter. Here, too, the pollutants emitted essentially depend on the fuel used, the type of heating, its age and its maintenance, the pollutants emitted are approximately the same as in vehicles with differences produced by coal and wood.
The pollutants emitted are the most varied, this is because there are many processes in the industrial field which therefore determine very different pollutants based on the processing performed, and can vary from solvents, acid mists to metals, dusts and more in the industrial field the emissions are highly regulated and for this reason industries must use pollutant abatement systems that vary according to the pollutants themselves, for example cyclones, bag filters, pocket filters and electrofilters are used for the poor; while for fogs or more generally for chemicals, activated carbon filters or wet filters are used.