For something like CFC concentrations in atmosphere, I would expect exactly the kind of curve the real data shows: initially a slow decline, followed by a middle period of relatively rapid decline...and that would be followed by "diminishing returns". This is how every chemical reaction works.
...but econazis go right to "Someone is making CFC-11!" Because they are idiots, they talk about an "uptick" in the gases rather than a reduction in the decline.
There is not more CFC-11 in the atmosphere; the concentration is merely declining at a lower speed.
And notice please what kind of magnitude we're talking about: parts per trillion. Okay, to find a gram of CFC-11 you need to filter it out of 4,400 metric tons of air, which is 3.55 million cubic meters of air.
I'm not even going to reiterate what I've said over and over and over again about how the ozone "hole" is a big nothing--discovered and explained in 1956, the magnitude of the decline in ozone has never changed significantly and it has recovered every year.