PCE is tetrachloroethylene, a chlorinated solvent, which is a manufactured chemical that does not occur in the natural environment. PCE was widely used as a metal degreaser by the military and industry since the 1940’s. Later, PCE was also used in dry cleaning practices. According to the California State Water Board, chlorinated solvents such as PCE and TCE (trichloroethylene) entered the environment through evaporation, leaks, and improper disposal because of poor handling and disposal practices. The EPA found PCE in more than half of all sites they have investigated. Because of the widespread use of PCE historically, it is found even in ambient outdoor air. Studies have shown that the outdoor air contamination is decreasing as the use of PCE is declining. When testing the indoor air of your dry cleaner, always compare your results to the ambient air concentrations outside because the PCE indoors may not be coming solely from your facility.