The cities that currently have the worst air quality anywhere in the world are all located along North America’s West Coast, where rampant wildfires have burned more than 4.3 million acres and have forced hundreds of thousands of people to flee their homes. Thanks to the fires, Portland, Oregon, currently has the world’s most polluted air, according to IQ Air, which monitors air quality around the world. Portland is followed by Seattle; Vancouver, British Columbia; and San Francisco. Just in case you needed another reason to wear a mask.