It is not pollution, it is the noise and the low quality of sleep that causes dementia. Good sleep quality is important so the glymphatic system that cleans the brain of garbage while sleeping can work well. See this recent article: https://www.scientificamerican.com/article/nedergaard-how-th...
I'll add my speculative observation to the mix: Pollution aggravates my allergies, and when I'm having an allergic reaction, I have poorer sleep.
I suspect this result may be reflective of multiple factors that remain to be associated, qualified, and quantified with respect to this overall correlation.
That was my first thought. I went to visit a friend in the middle of nowhere in Norway last year. Coming back to a big city a week later I really noticed the level of noise you get in a big city and found it quite hard for the first few days back.
Had a similar experience recently overseas. Was shocked at how quiet it was--and I"m not like living in NYC or something back in the US--it is a clear difference from even a smaller city.
i wonder how much the road noise is affecting me especially since I quite like the overnight hum of the roads. a highway provides a much more even white noise experience while city road noise is more grainy.
the closest experience to the city hum that i could find in the country is probably the seaside, and i have to say, it is a very comforting experience.
PM2.5 particles from vehicle emissions are small enough to penetrate the blood-brain barrier and have been shown to end up in brain tissue.
Even if it isn't a direct cause of dementia, air pollution contributes to cardiovascular diseases which are themselves risk factors for dementia.