Kev nqus cov tshuaj nqus pa (MDI) tau tsim nyob rau xyoo 1950, thaum tus neeg tshaj tawm isCFCs (Chlorofluorocarbons). CFCs tau pom ua rau rhuav tshem ozone txheej siab siab tshaj lub ntiaj teb. Montreal Raws Cai tau tshaj tawm thoob ntiaj teb kom txo qis cov CFCs siv, kom txo qis ozone tawm. CFC's tau siv ntau yam khoom lag luam, suav nrog MDIs. Lwm cov cuab yeej siv tau tsim tawm los hloov CFC cov npe hauv MDIs. Cov khoom siv ua hmoov qhuav .TheHydrofluoroalkane Propellant, luv luv rau HFA propellant, tseem hu ua Hydrofluoroalkane 134a, yog hloov rau cov txheej txheem CFC propellant.
