Propane is probably purer than straight-up NG, but it's exhaust is still exhaust.
getting radon out does not cost money
Probably other toxins are more important: mercury vapor and hydrogen sulfide are usually mentioned. Hydrocarbons other than methane may burn to carbon monoxide or soot. Gas is said to get much less processing before delivery than it used to.
SpaceX will probably purify theirs before pumping it aboard, just to increase the useful life of their Raptor engines.
Best case you have a hood that vents to the outside. Hoods really work
If the vent moves more than a certain amount of CFM air, then an exchange system is required, but that takes almost a restaurant grade vent to get to.
Most people keyed into this from the Vox article:
https://www.vox.com/energy-and-environment/2020/5/7/21247602...
Which links to:
https://www.osti.gov/biblio/1172959
As evidence for the claim that Gas range put out more PM2.5
But if you consult table 3 of that article you will see it doesn't show that at all. The food (especially frying) swamps differences between electric vs gas ranges, which themselves aren't even significant.
I wonder how much of the gunk is still in my lungs.
I took apart mine and completely greased all the fittings and put the proper type of teflon tape. Feel way better. Confirmed there are zero leaks now