However, its harmful effect to the atmosphericozonelayer has been deeply concerned by the international society. Much research works have been done to seek for the substitutes of them.
但其对大气臭氧层的破坏作用，已引起了国际社会的高度重视，各国对其替代产品的研究做了大量的工作。
2
The basic principle of atmosphericozonelayer destruction hy polyurethane blowing agent CFC-11, and various way, developmental trend and economic feature of substitution for CFC-11 were reviewed.
Once photosynthesis had raised atmospheric oxygen levels high enough, the ozonelayer formed, meaning that it was then possible for living things to venture onto the land.