The word smog derives from the contraction of smoke (smoke) and fog (fog). It is used to speak of a polluting fog that is produced in large cities during long periods of high pressure (anticyclones) that prevent pollutants from dissipating.
There are two types of smog:
- Acid smog. Formed by the high concentration of suspended particles (fumes), SO2 from vehicles, heating systems and industries, which are combined with fogs, where the atmosphere has high humidity and an anticyclonic situation. It is characteristic of cold and humid cities, in winter, and caused by primary pollutants. It produces respiratory alterations (they affect asthmatics more), and it damages the leaves of the plants.
- Photochemical smog. It occurs when nitrogen oxides and hydrocarbons from the burning of fossil fuels react with the energy of ultraviolet solar radiation, causing a cloud of oxidizing pollutants such as tropospheric ozone. It causes irritation of the eyes, mucous membranes and skin, respiratory problems, allergies, cardiovascular problems, etc.