The amounts the researchers measured at ground level will take three to five years to drift up into the stratosphere and make a difference in the stratospheric layer, where the actual ozone destruction occurs. But seeing a tiny dip in the ground-level sum of the chemicals convince Montzka that we have taken the right step to begin the recovery!
(The Nation, June 13, 1996)
"A tiny dip" in the last paragraph refers to _________.
the little reduction of ozone-destroying
the small layer of ozone destruction
a little step to begin the recovery
a difference in the stratoshperic layer