Many cities across the U.S. have had success lowering harmful ground-level ozone in recent years, but the exception to that trend is in the American West. Just last summer, the Front Range — and Denver in particular — recorded some of the worst air quality levels on the entire planet.
READ MORE: Western Boom Cities See Spike in Harmful Ozone
Colorado Edition spoke to Kaiser Health News environment reporter Jim Robbins, who helped explain this trend.