Easy to imagine vascular dementia rates being higher due to air pollution, would be interesting to see if rates of non-vascular dementia, such as Alzheimer's are also higher.
According to the press-release, a difference in distance of only 50m from a high-traffic road creates an observable 7% difference in dementia risk.
I'd say it's very easy to both live in a city centre and live 50m away from a major road.