The chemical processes in which it is involved should work without hindrance, and ozone levels will drop.

它涉及到的化学过程如果不受妨碍的话，空气中的臭氧含量就会下降。

youdao

Scientists use "hole" as a metaphor for the area in which ozone concentrations drop below the historical threshold of 220 Dobson Units.

科学家们用“空洞”一词表示臭氧浓度低于220个多布森单位（多布森单位是用来度量大气中臭氧柱尺度的单位。

youdao

Scientists believe that ozone depletion in the atmosphere will continue until levels of ozone-destroying Cfc's drop to pre-1970 concentrations, around the middle of the next century.

BBC: News | Sci/Tech | Ozone hole reaches record size