Air pollution consists of contaminating gases and particles present in the atmosphere. Gaseous pollutants include sulfur dioxide (SO2), nitrogen oxides (NOx), ozone (O3), carbon monoxide (CO), volatile organic compounds, toxic pollutants, and some gaseous metals.
All the mentioned factors have a bad effect on human health, as well as on the environment. Of these, the most dangerous are probably toxic pollutants, which include gases, namely: hydrochloride, aromatic hydrocarbons such as benzene and toluene, dioxin; then compounds such as asbestos, and elements such as cadmium, mercury, and chromium, as well as radioisotopes of radium and uranium. The U.S. Environmental Protection Agency has classified as many as 187 pollutants as hazardous. These pollutants are known to cause a variety of health problems and serious illnesses, such as cancer, which is the second leading cause of death in the world after a heart attack. Also, some of these toxic substances enter the soil and watercourses, and thus enter the food chain through animals and plants to humans.
The main sources of toxic pollutants are thermal power plants, industrial steam generators, paper mills, landfills, fossil fuels released by cars, etc. One typical example of a toxic gas is tear gas in mass rebellion control.
Strategies for controlling toxic pollutants are the introduction of new clean energy sources, modifications to industrial processes and the introduction of standards for various materials, coal cleaning (to control mercury), gas and particulate washers, as well as reformulated gasoline and diesel fuel. Although there are new technologies and laws to control the emission of toxic pollutants, progress in combating them is still not fast enough and requires more stringent and effective measures globally.