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Rural West sees more smog; now scientists may know why

UPDATED: March 3, 2017. Photo location was corrected in caption: The city depicted is Denver, not Boulder, Colo.
March 1, 2017
Ground level ozone, shown here in Denver, is a growing problem in the western United States.

Ground-level ozone, also known as smog, has climbed in the rural West over the past 25 years, even in such seemingly pristine places as Yellowstone National Park. Now, scientists may have found out whyoffsite link – and why cutting our own output of smog-forming chemicals such as nitrogen oxide hasn’t helped.

Researchers from NOAA’s Geophysical Fluid Dynamics Laboratory and Princeton University found that increased pollution from Asia, which has tripled its nitrogen oxide emissions since 1990, is to blame for the persistence of smog in the West, despite American laws reducing the smog-forming chemicals coming from automobile tailpipes and factories.

Smog has decreased overall in the eastern United States, even though levels can spike during heat waves.

Ozone can be harmful to human health, causing asthma attacks and difficulty breathing. It can also harm sensitive trees and crops.