I left my car running as I was working on it and suddenly there was a nose-burning gas from somewhere. Maybe ammonia or chlorine. Does anyone have any idea what's going on?

Might just be the catalitic converter starting to do its thing. Did you start the car from cold ??

Might just be the catalitic converter starting to do its thing. Did you start the car from cold ??

I started the car around 1pm when it was very hot. Or do you mean had I been anywhere earlier - no I hadn't.

Maybe just a coincidence but my air con doesn't work now,and it was fixed only a couple of weeks ago.

It was quite a horrible smell.

I distrust coincidences.

If the air con stopped working, maybe start your search there. Burning rubber smell ?? Maybe the compressor clutch went south and the smell was the belt burning.

Or the rotten egg smell associated with LPG ??

Hard to troubleshoot without knowing all the symptoms.

Sounds like Freon or R32 gas from your A/C. Both have that type of smell and if you had work done on it and the system was then recharged it is not uncommon for a new part failure on an old system such as the evaporator that is in the car. The new parts and system recharge puts more stress on other old parts.