[bawolff]

According to wikipedia, california limits to 0.05 ppm and the more sensitive people start to smell it at 0.1ppm.

So if you can smell it, that's probably not great.

[uuidgen]

I don't think you can smell ozone - it's rather noxious. I think what you can smell as "thunderstorm" is the air cleaned a bit by ozone and the process of ionization (which traps some bigger particles).