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Particulate matter pollution climbs in US, reversing years of decline

Industrial boilers, diesel vehicles, and use of natural gas drive increase

by Cheryl Hogue
October 27, 2019 | A version of this story appeared in Volume 97, Issue 42


Photo shows vehicles on highway with large truck blowing plumes of exhaust from its upright twin exhausts.
Credit: Paul Marcus/Shutterstock
Researchers say exhaust from diesel-powered vehicles helped boost the level of fine particulates in the US since 2016.

Particulate matter air pollution in the US rose 5.5% from 2016 to 2018, according to an analysis from a nonprofit economic research group. The increase reversed a 24.2% decline in fine particulate pollution from 2009 to 2016.

Causes of this change are increases in both economic activity and wildfires and a decrease in enforcement of the Clean Air Act, says the analysis, released by the National Bureau of Economic Research. Most of the pollution increase took place in the Midwest and West.

The two authors, economics professors at Carnegie Mellon University, examined data on the makeup of fine particulate matter, which is 2.5 µm in diameter or smaller. Exposure to particulates of this size is linked to cardiovascular and lung problems.

After controlling for particulates from wildfires, the analysis found that elemental carbon fine particulates rose nearly 21% from 2016 to 2018. The authors determined the increase in carbon particulates came mainly from diesel vehicles and some industrial boilers running on coal or fuel oil. During the same period, nitrate particulates rose 7% because of greater use of natural gas in electricity generation and by households and industry.

Meanwhile, the level of fine particulate sulfates, which come chiefly from coal-fired power plants, has dropped nationwide since 2009. It fell by 9% from 2016 to 2018 as the use of the plants declined and remaining facilities added pollution controls, the analysis says.

The US Environmental Protection Agency is in the process of deciding whether to tighten the current health-based standard for fine particulate matter of 12 µg/m3 of air as an annual average.



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