In Steel Country, the Fight for Clean Air Faces New Obstacles
A Japanese steel giant has pledged billions in new investment in Pennsylvania’s Monongahela River Valley, raising hopes that it would clean up pollution from its steel mills in the region. But documents show that its plans to ramp up production will worsen local air quality. Read more on E360 →
The Monongahela River, stretching 130 miles north to Pittsburgh from West Virginia, flows through the steep-walled Mon Valley, a region dotted with small towns and forested hillsides. Though picturesque, this area has a history of pollution and ongoing struggle for clean air. In 1875, Andrew Carnegie initiated his first steel mill in Braddock, marking the beginning of a century-long era of heavy industry.
By 1901, U.S. Steel had emerged from Carnegie's company's merger. The Mon Valley was once the hub of domestic steel production, yet the air was often filled with smog. Between 1970 and 2020, nationwide emissions of key air pollutants declined by 78 percent. However, the Mon Valley's improvement has been uneven. The American Lung Association's 2026 State of the Air report ranked Allegheny County, which encompasses the Mon Valley, among the nation's most polluted areas, citing failing grades for unhealthy ozone levels, spikes in fine particulate pollution, and persistent exposure to these particles throughout the year.
The public health consequences are significant: a 2019 study published in the Annals of Global Health estimated that in 2019, 12 percent of adult deaths and over 400 adverse birth outcomes in the greater Pittsburgh region were linked to air pollution. Moreover, childhood asthma rates in Allegheny County hover around 11 percent, compared to the national average of 6.7 percent.
The latest EPA records reveal that a coking plant in the Mon Valley has violated Clean Air Act regulations for 12 consecutive quarters. The valley may now be at a turning point. Federal industrial policy has redirected funding toward manufacturing nationwide, and the recent acquisition of U.S. Steel by Japanese corporation Nippon Steel brings billions in investment and plans for a new manufacturing facility.
However, Nippon is reportedly increasing coal usage by constructing a new hot strip mill, which will exacerbate emissions of various pollutants, as documented by the Pittsburgh-based Group Against Smog and Pollution (GASP). Local resident Patrick Campbell, GASP's executive director, expressed skepticism about U.S. Steel's commitments to reduce emissions or invest in facilities.
The primary sources of air pollution in the Mon Valley are the three steel mills at the Mon Valley Works, which emit particulate matter, benzene, ammonia, sulfur dioxide, and hydrogen sulfide. The Edgar Thomson Steel Works in Braddock also contributes to pollution through its blast furnaces. In its latest compliance monitoring, the plant had violated Clean Air Act regulations for nine straight quarters.
Upstream, the Clairton Coke Works utilizes large ovens called batteries to bake coal into a fuel called coke, which powers blast furnaces. This process generates particulate matter and harmful gases, directly responsible for asthma, respiratory diseases, heart failure, arrhythmias, strokes, and even neurologic problems. According to the EPA's data from July 2025, the Clairton plant violated Clean Air Act regulations in the previous 12 quarters.
As the leading emitter of hydrogen sulfide in Allegheny County—accounting for over 72 percent of the state's emissions and nearly 93 percent of the county's—Clairton is a major contributor to air pollution. Between March 2022 and November 2023, hydrogen sulfide levels exceeded state standards 159 times at the monitor nearest to the coke works, often at levels deemed "major severity."
The topography of the Mon Valley also exacerbates air pollution. The factories' stacks do not rise above the surrounding rocky walls, and the valley is prone to inversions, trapping pollutants near the ground. Despite pollution controls and the closure of four batteries at the Clairton Coke Works, air quality monitors in the Mon Valley still frequently record spikes in particulate matter, ozone, and sulfur dioxide that surpass federal safety thresholds.
U.S. Steel has claimed a 99 percent compliance rate, but the Allegheny County Health Department reports that the valle's air quality monitors continue to record violations.
Written by urgent.news from Yale Environment 360's reporting — not their text. Machine-written — may contain errors; check the original before relying on it.
