Smog-producing air pollution declining more slowly


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Catalytic converters have decreased the amount of carbon monoxide emitted by cars dramatically since they were first introduced in the 1970s. (Chris Keating/flickr)
Jenna Ladd | May 1, 2018

A new study found that levels of two primary pollutants in the U.S. atmosphere have not been declining as rapidly during recent years as they once were.

Researchers at the National Center for Atmospheric Research (NCAR) studied satellite data and ground level measurements of two smog-forming pollutants: nitrogen oxides and carbon monoxide. Levels of these air pollutants decreased dramatically following the implementation of the Clean Air Act in the 1970s. Requirements of that act pushed automakers and energy-producers to develop new technology which curbed the emissions of these two pollutants.

The study found that concentration of these two pollutants in the atmosphere decreased by seven percent each year between 2005 and 2009. However, from 2011 through 2015, the pollutants’ levels only shrunk by 1.7 percent annually.

Helen Worden is a scientist at NCAR and one of the study’s authors. She said to Phys Org, “Although our air is healthier than it used to be in the 80s and 90s, air quality in the U.S. is not progressing as quickly as we thought. The gains are starting to slow down.”

The study noted that the slower decrease in carbon monoxide and nitrogen oxides was especially severe in the eastern part of the U.S. This finding dispels notions that the slower pace can be attributed to traveling air pollution from countries like China. The positive news is that the slower decline in carbon monoxide, which is primarily emitted by vehicles, is likely due to the fact that major strides have already been made to reduce vehicle emissions. In short, clean air technology related to cars may have reached a kind of plateau.

This study was funded by NASA, the National Oceanic and Atmospheric Administration, the University of Colorado Boulder, and the National Science Foundation. The full journal article can be found in the Proceedings of the National Academy of Sciences.

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