Abbreviation of volatile organic compounds which are chemicals that contain carbon, hydrogen, oxygen, fluorine, chlorine, bromine, sulphur or nitrogen, present in living organisms and that easily become vapors or gases. They are released in the burning of fuels such as gasoline, wood, coal, or gas, in the use of solvents, paint and home products, as a moth repellent, flavouring substances in aerosol, air... They are volatile, fat-soluble, toxic and flammable and its source can be natural or artificial. The most common natural source is methane, generated by the decomposition of organic matter, as it takes place in the digestive system of ruminants like cows. The artificial origin is in industrial activities: paints, footwear, iron and steel industry... Many of these products are hazardous air pollutants.