Air pollution is the presence in the atmosphere of contaminants or substances which represent a serious threat, risk or harm to the safety or health of the population or the environment.
The main polluants affecting our health are sulfur dioxide (SO2), nitrogen oxides (NOx) and particulates. These contaminants may be directly emitted into the atmosphere (primary pollutants) or formed from primary pollutants that react in the atmosphere (secondary pollutants).
Examples of the latter are tropospheric ozone, which is formed in the presence of sunlight from volatile organic compounds (VOC) and nitrogen oxides (NOx); nitrogen dioxide, whis is formed by the oxidation of NO; and acid rain, which is formed when sulfur dioxide or nitrogen oxides react with water.
These pollutants have negative effects on human health (eye, nose, throat and lung irritation at low concentrations) and the environment, as they contribute to acidification and eutrophication, as well as the subsequent formation of particulates and tropospheric ozone (photochemical smog).
SO2 and NOx are mainly produced from the combustion of fossil fuel in high-temperature industrial processes and electricity generation.
Particulates are related to any type of industrial combustion and heating. Particulates and NOx are also related to traffic and transportation in general.
There are air quality surveillance booths throughout Spain measuring the concentration of these parameters. This information is available to the public and is used to determine if pollution levels in any particular area exceed the maximum permissible levels for health and the environment.