The 9-county North Front Range has been out of EPA compliance for ozone pollution for years. As of 2015, the EPA maximum is now 70 parts per billion of ozone pollution in the air we breathe (it was at 75 ppb in 2008). The region's 3-year value for what is known as the 8-hour ozone trend -- which the EPA checks -- was at 79 last year. That's a lot better than it was a decade ago, considering that there are more people, cars and industrial sources of emissions now in the area. But the amount of pollution is still higher than the EPA allows and the region could face federal penalties if it remains out of compliance.
Source: Regional Air Quality Council
Chart: Tamara Chuang | Data Design: Eric Lubbers