dirty air over downtown denver, r m

dirty air over downtown denver, r m

FILE – Pollution obscures the skyline of downtown as the sun rises over Denver, on Feb. 28, 2019. The Environmental Protection Agency is delaying plans to tighten air quality standards for ground-level ozone — better known as smog — despite a recommendation by a scientific advisory panel to lower air pollution limits to protect public health. (AP Photo/David Zalubowski, File)