Between 1990 and 2014, ozone levels in 33 U.S. national parks were about the same as in the 20 largest urban areas, according to an analysis published in Science Advances. High ozone levels result in reduced visibility, and attempts to control haze and air pollution through regulation have proven costly and somewhat ineffective.
The researchers analyzed maximum daily 8-hour ozone concentrations in the parks, as well as the number of days in which the maximum daily 8-hour ozone concentration exceeds 70-parts-per-billion (ppb). When they compared their results to levels found in cities like Los Angeles, New York, and Chicago, they found no statistical difference.
During the 24-year study period, summer ozone levels decreased in urban areas by an average of 13 percent. Ozone levels in national parks increased from 1990 to the early 2000s, and then began decreasing. Air quality alerts issued by the U.S. National Park Service, as well as limited visibility caused by high ozone levels, can result in fewer people visiting and enjoying the parks.
Sourced from: Science Advances