The air planes could be easily stopped with a no fly zone. The problem lies in artillery delivery systems like the SCUD and especially Frog-7. You can’t stop these without putting in advanced missile defence systems like the Patriot and those are out of the question.
You could go “Scud Hunting” but those types of missions were completely ineffective during the Gulf War.
The only hope is that the report mentions it being loaded on plane bound munitions rather than ballistic missile warheads.
EDIT: I just remembered something about Sarin Gas. Since it’s heavier than air, it will seep down, so higher buildings are a must. Rooms with windows are out of the question: If Assad uses the same strategy as Saddam, they’ll shell the area first to break the windows (I doubt there are any unshattered windows remaining in Aleppo).
Sarin will dissolve in water, food and clothes and contaminant it. Sarin quickly disperses when a vapour but lasts longer as a liquid.
AND NO FIRE! NO Aluminium! Sarin is combustible and eats through tin, cadmium, aluminium which results in hydrogen gas forming.
The only good news is that Sarin gas degrades quickly. IN air, it might disperse in as little as ten minutes. It degrades a bit slower in water but also under 1 hour (though to be safe, leave it for quite a few hours before drinking anything)
Any clothing contaminated with Sarin vapour can transmit it. CUT the clothing off (don’t pull it over your head) and toss it in a plastic bag and then toss THAT into a plastic bag. Soap and Water can actually be a good stop gap decontaminate, wipe the body down with it and don’t use the same sponge/cloth twice.