In a large-scale study of nearly 28 million older Americans, researchers found that long-term exposure to PM2.5 air pollution is associated with a higher likelihood of developing Alzheimer's disease.[1] The link comes largely from the direct effects of pollution on the brain, not from related conditions like hypertension or depression. People in more polluted areas had more toxic proteins in their brains and faster cognitive decline. An analysis of the brain tissue of 602 deceased patients confirmed a direct link with air quality and the severity of Alzheimer's pathology. For every microgram of PM2.5 per cubic meter, the chance of more extensive amyloid plaques increased by 17% and of more advanced tau tangles by 20%. The overall level of Alzheimer's pathology was 19% more likely in the more severe category.[1] This association was specific to Alzheimer's disease, not to other brain diseases such as Lewy bodies or vascular lesions.[1]