More than 99% of the phosgene produced is used on-site in closed
systems. It is produced by reacting equimolar amounts of anhydrous
chlorine and carbon monoxide in the presence of a carbon catalyst.
World production has been estimated to be greater than 3 million
tonnes. Environmental phosgene levels arise from industrial
emissions and thermal degradation of some chlorinated solvents and
chlorinated polymers. However, a significant source of environmental
phosgene is the photochemical oxidation of chloroethylenes such a tri-
and tetraethylene.