Here's an idea, your highly polluted areas near the airport could be zoned low-density residential to make low-income residential neighbourhoods. I remember the city planner advisor saying it's important to have those neighbourhoods in a city, especially since you have mansions taking over old neighbourhoods. Essentially, it's like there's a gentrification mechanic or something in the game. ...Potentially, this lack of affordable housing could also be what's hurting your industrial demand. Also, building a metro downtown should help to get rid of all those parking garages! 😊👍