Having trouble breathing in the metro? Well it turns out it's not the best air to breathe. A new study shows that Denver is actually the 4th worst city in the entire country for air pollution. The study looked at how many days we had moderate of unhealthy air quality which averaged 274 days in 2019. YIKES. San Bernardino, Phoenix, L.A. all had more days with bad air quality and San Diego rounded out the top 5.