In a recent study, more than 270,000 people were followed for almost 20 years in six European countries where regular measurements of outdoor air quality take place. In the open air, the researchers looked separately at particulate matter (solid particles smaller than 2.5 micrometres, often contaminated with heavy metals), nitrogen dioxide, black carbon and ozone. The first three showed a positive link to death from Parkinson's; ozone did not. Particulate matter seems to be the most strongly related to Parkinson's, strikingly also at exposure levels below the 'safe' European limit values.
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The conclusion is that this study is strong evidence of a link between air pollution and death from Parkinson's disease, and that long-term exposure to particulate matter contributes most to this.