Air quality in American West among the worst in the world

The air quality in Portland has become the worst in the world — with Seattle, Los Angeles and Denver also ranking up there with notoriously polluted places like Delhi and Shanghai.

Why it matters: Big-city residents often consider themselves smugly immune to the physical wreckage of calamities like wildfires, floods and hurricanes. The pernicious smoke now blanketing the splendid cities of our nation's Western spine is a reminder that no one is exempt from climate change.

Where it stands: The EPA maintains a map on its website of the current air quality across the U.S. As of Thursday morning, Portland, Denver, Seattle, Fresno and countless smaller metropolises were girded by contour bands that signified "unhealthy," "very unhealthy" and "hazardous" air.

• From Vancouver to Tijuana, the ozone and air-quality situation looked grim.
• The threat is particularly grievous for children, the elderly and people with conditions like asthma or heart or lung disease.
• Cloth masks won't protect against dirty air from wildfires, but N95 respirators — when worn correctly — can help.

Flashback: It's unthinkable to most Americans that Portland — which for years was lovingly mocked in the series "Portlandia" for its hyper-liberal eco-values — now has the worst air in the world, with an air pollution level deemed "hazardous."

• The Air Quality Index (AQI) in Portland recently measured a whopping 303, according to a firm called IQAir; the runner-up city, with a measurement of 170, was Hanoi.
• You can see a table of the cities around the world with the dirtiest air and their AQI readings here. The current top 20 include Portland, Seattle, Delhi, Los Angeles, Denver, Shanghai and Lahore.

Silver lining: San Francisco's air quality is currently considered "good."