Yes, I did discover that Syria hadn't signed up to the CWC, but they are signed up to the Geneva Convention that prohibits the use of Chemical weapons, if not their storage and transport.
As to the last thought, "...military intervention could result in a far worse situation," I just find that hard to believe. What is going on in Syria is already far worse than it should have been, had we intervened earlier. Now is only the time because we are already too late, in my opinion anyway. Again, there's nothing special about Syria except for the feeling that we can do something and therefore that we should. Intervening elsewhere -- well, I'm a bit of an interventionist when it comes to foreign policy, so if there's a moral case for intervention, and if it has a prospect of improving the situation, I'd be in favour. (I suppose this makes me a Blairite.) This view may have been discredited by Iraq and Afghanistan, but I can't help but feel that this was because in those two countries the intervention wasn't done "properly", that a better job of rebuilding the country and we would be hailing them and the policy as successful. So, even though in practice intervention doesn't always work, I don't think that's because the principle is wrong. And Isolationism doesn't work, either. If we stay out of Syria there is just as much reason to worry that the situation will deteriorate. There's no sign, for example, that Assad if he wins will go easy on the losers.
The mission I envisage isn't one where we take a particular side. It's now too late for that, anyway. Rather, it should be something along the lines of a peacekeeping mission coupled with real efforts to force both sides to the table. I don't see that this can happen as long as Assad -- or indeed the rebels -- can be confident of winning the Civil War so that he has no need to negotiate anyway.
It's now up to France and the US to see what they choose to do. If they end up not intervening either, well, we'll never find out if intervention would have worked. But, again, I struggle to see how it would have made things worse.