Carbon tetrachloride is still used as a refrigerant and an aerosol propellant but, these uses are being phased out. Carbon tetrachloride appears to be a regional or transported pollutant as the concentrations do not vary significantly from urban sites to rural sites. The atmospheric half life of carbon tetrachloride is 50-100 years, indicating that it will take a long time for current concentrations to decrease . Chloroform has been found in the air from all areas of the United States. Sources of chloroform in the atmosphere are pulp and paper mills and water and wastewater plants that use chlorine as a disinfectant.
Chloroform appears to be a transported pollutant.
The concentrations do not vary significantly from urban to rural sites and the compound has an atmospheric half life of 2-3 months. Formaldehyde Formaldehyde has numerous atmospheric sources. The compound is a byproduct of combustion, which covers a wide range of sources from internal combustion engines to wood stoves. Formaldehyde is also generated by wood processing plants and glues. Formaldehyde is produced by the atmospheric reactions of other pollutants, including 1,3-butadiene.