well i thought about it but its tricky because lots of people hate having downsides to stuff, so if i add something like smog people will want anti smog devices so they can keep building more stuff, or they will try doing stuff like shoving all the buildings into a room and expect the fumes to just get trapped in there so they are no longer a problem, so if i did do something like fumes it would take a lot of work to cover all the scenarios, and then id have to make it an optional thing thats disabled by default else i'll ruin people saves, which means most people wont even know its a thing so it would be a lot of work for something not many people will use, which tends to be the case with most of my mods, once you lock in a certain kinda play style its very tricky to introduce large changes, even small changes in my other mods like hygiene caused havoc, or like when i added the whole bill system to rimefeller it caused a bunch of debate

Cool, not unexpected. Modding is generally a thankless job. Although if you change your mind, I would suggest using the same code as the temp system, so that vents spread whatever sort of airborne pollution out.