This is a citation needed comment to me. It's one heck of an assertion that I have never heard. Most folks I've chatted with who have made this transition do it because of the density of people, not the pollution (which is miles better in cities than it was even 20 years ago).
The first and biggest pollution is the noise. The ambient car noise has a huge effect on stress level and sleep quality. When you remove the car from the city, it's almost at silent as the countryside.
The second is the danger in the street. Your brain registers those big fast moving cars as potential danger to avoid and raises your stress level and makes you want to move away from it.
The third one is the space the car take. When you remove the cars you have the opportunity to either make things easier to walk to, or to add parks and greenery. When you remove cars, modern cities are surprisingly empty, much less dense than a village.
Then there's the air pollution.
What do you plan on doing about emergency vehicles and their sirens and construction? Those are by far the biggest sources of noise for me in a city. Normal car traffic is omnipresent but usually has a fairly low ceiling that doesn't go through walls all that much.
Normal car traffic absolutely goes through walls, you think you are used to it, but it actually stresses you quite a lot.
Construction work can be an issue indeed
As it is in suburbs too. My parents' house is fairly quiet, until a neighbor is hammering or sawing. And that doesn't even include the loud insanity of lawn mowing in the desert.