NO and OH catalysts are not significant threats to stratospheric ozone because the concentration of NO in the stratosphere is very small (there is not a lot of N₂O in the atmosphere) and OH is so reactive that it does not survive the slow diffusion up through the stratosphere (that is, it tends to react with other stuff on the way up), or the ones from the rare stratospheric water molecule end up reacting with other things before it gets a chance to destroy much ozone.

A study was done a long time ago on the effects of emissions from supersonic transports (SST) in the stratosphere (it was predicted that by now, much of the intercontinental air travel would be by Concorde-like aircraft flying in the stratosphere). It was thought that the NO in the exhaust would increase the depletion of stratospheric ozone. Of course, we don't have the sort of air travel occurring very often(nor spacecraft like the Space Shuttle), so it's moot. Also, there is some speculation that the large number of aircraft flights in the stratosphere might leave enough of other combustion products in the exhaust to create a "smog" problem in the stratosphere, which would add ozone to the region.

Atomic bromine (a single atom of bromine as opposed to a molecule of bromine, Br₂) and chlorine (Cl) are more significant threatsto stratospheric ozone because the compounds containing thm have long atmospheric lifetimes. They have time to slowly diffuse up through the stratosphere, where they can be broken to their atomic components near the ozone layer.

There has been recent legislation to reduce the emission of the compounds that lead to the seeding of the ozone layer with atomic bromine and chlorine. Halon fire extinguisher production has been halted, and Freon refrigerants are being substituted by similar substances that have shorter atmospheric lifetimes (which would prevent them from diffusing as far as the ozone layer). Methyl bromide soil fumigation has been severely curtailed or banned in many places because of its toxicity to humans and wildlife while at the ground, so the reduction has the secondary effect of reducing the potential for depleting the ozone layer.