Some of this chloride combines with hydrogen to form hydrogen chloride. Some coal-burning power plants use pollution control devices to remove sulfur from gases leaving their stacks. Chloride-bearing wastes captured by pollution control devices are usually sent to ash ponds or land disposal sites. Almost all hydrogen chloride from power plants comes from burning coal. Most hydrogen chloride released into the air by natural sources comes from volcanoes.
Smaller amounts come from forest fires, weathering rocks, and dust.
Hydrogen chloride released into the environment by human activities outside the utility industry comes mainly from industrial boilers that burn coal and oil, incinerators that burn refuse, automobiles that burn gasoline, and plants that manufacture aluminum, plywood, and particle board. Industries reporting to EPA released 32,670 tons of hydrogen chloride into the environment in 1996. Nearly all was released into the air. Hydrogen chloride released into the air from power plants easily dissolves in airborne water to form dilute hydrochloric acid. Some of this hydrochloric acid forms tiny liquid droplets or thin films on tiny dust particles.