Multnomah County residents breathe the dirtiest air in the state and face the highest risk of pollution-related cancer, due in large part to the region’s cars, trucks and trains.

Industry, construction sites and unplanned events add to the region’s pollution problems.


Diesel particulate is made up of dozens of chemicals, the bulk of which is black carbon, the soot so often associated with pollution. It is dangerous in part because the particles are so small — about one-400th the diameter of a human hair.

The Environmental Protection Agency regulates six air pollutants under the Clean Air Act including ozone and lead, but diesel particulate matter — known as diesel PM 2.5 — isn’t among them.

Industry Emissions

Between 2013 and 2016, the U.S. Forest Service identified heavy metal hotspots in Portland. At the time, Oregon's emission rules were based on federal law, and allowed industrial facilities to release potentially harmful amounts of air toxics. Those findings spurred a public demand for action.

In 2016 Gov. Kate Brown announced an initiative to establish emission limits based on toxicity, in addition to the proximity of those emissions to people. That initiative Cleaner Air Oregon, sets health-based limits on more than 250 air toxics.

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