Air Pollution

Naturally, the atmosphere contains a lot of dust as well as solid and liquid particles in suspension (aerosols). These particles come from diverse sources: marine (sea spray), mineral (erosion of sand by the wind), volcanic (ash blown during eruptions), biological (bacteria and pollen), and meteorite (dust left by the passage of a meteorite). These fine particles play an important role in the atmospheric composition and in the regulation of climates since they form condensation nuclei which promote the formation of clouds.

Since the rise of the industrial age, human activity has dramatically increased the input of large amounts of particles, gases, and various chemicals into the atmosphere. Some of these substances are similar to those emitted from natural sources; however, some do not even exist naturally. Thus, hundreds of substances are released into the atmosphere modifying its chemical composition and natural properties.

Air pollutants can be grouped into two broad groups: primary pollutants and secondary pollutants.

• Primary pollutants are emitted directly from human activities, such as the production of electricity from fossil fuels, transportation, heating, and industrial processes. There are generally five main primary contaminants: suspended particles, sulfur dioxide, carbon monoxide, nitrogen oxides, and volatile organic compounds.

• Secondary pollutants, on the other hand, result from the chemical transformation of primary pollutants in the atmosphere. For example, nitrogen oxide molecules are transformed in the troposphere into tropospheric ozone. This type of ozone is, among other things, responsible for the phenomenon of smog.

Various anthropogenic sources derived from primary air pollutants.

The primary pollutants that contaminate the atmosphere have many effects, both on human health and on the environment. For example, prolonged exposure to low concentrations of certain pollutants is likely to increase the risk of disease. Many respiratory illnesses result from inhaling air pollutants: asthma, emphysema, chronic bronchitis, sinusitis, and allergies. In addition, by damaging lung tissue, fine particles in the air increase the risk of lung cancer. Aside from affecting human health, pollutants disrupt the functioning of ecosystems by acting on soils, vegetation, and animals.