In mid-December, the state of Pennsylvania issued a warning to residents in the Mon Valley: The forecast wasn’t about the snow but about the poor quality of its air during a temperature inversion.

This follows a streak of poor air quality last winter, and more recently. One day in November, air pollution in the Mon Valley reached 129 micrograms of fine particulate matter. The 24-hour standard set by the Pennsylvania Department of Environmental Protection [DEP] is 35 micrograms per cubic centimeter (µg/m3). This level is considered especially unhealthy for sensitive groups like children, the elderly and people with asthma

The air also exceeded the state standard for hydrogen sulfide for seven days straight during a temperature inversion in early November. After a prolonged inversion that trapped pollution in December of 2019, the county promised it would create a new rule this year to lessen the negative health impact on nearby residents

“While we will continue to advocate for residents to do what they can to reduce emissions, we must also explore new regulations that would impose corrective action requirements on industry during short-term pollution events,” Ronald A. Sugar, then-interim director of the health department, stated in a January press release. 

Nearly a year later, a potential new rule is taking shape. A subcommittee of Allegheny County’s Air Pollution Control Advisory Committee is considering the draft of a rule that would require industrial polluters like U.S. Steel to reduce emissions when a temperature inversion traps in pollution that exceeds EPA standards. The committee makes recommendations on air quality regulations to the Allegheny County Board of Health.

U.S. Steel has said it already is reducing emissions and that, during the most recent inversion, pollution was high in other parts of the county and state as well.

“During the recent inversion, we were already operating at a reduced level. We made additional adjustments to our operations when the inversion began,” Meghan Cox, manager of external communications at U.S. Steel, wrote in an email to PublicSource. Elevated emissions readings in other areas “suggests region wide issues such as mobile sources and background levels from other areas are contributing to elevated levels during inversions.”

Inversions, a weather phenomenon common during winter that traps cold air under a lid of warmer air, keeps pollutants from dispersing from sources such as cars, households and industrial facilities like U.S. Steel’s Clairton Coke Works. 

“When there’s a strong inversion, the mixing height of the region is depressed,” said Mark Dixon, an air quality advocate in the Pittsburgh area. “And if the same amount of pollution is being emitted, but it’s trapped right here, then you’ll see spikes in the air pollution where the people are.”

Although overall air pollution has been trending downward for decades in the county, pollution in the Mon Valley is often still some of the worst in the country and asthma rates are disproportionately high, particularly among Black children

The Allegheny County Health Department has increased fines for violations, added staff and joined new lawsuits to reduce the ongoing pollution at U.S. Steel. But until now it hadn’t proposed a rule addressing air quality during inversions

During a Dec. 8 meeting, the regulation subcommittee of the county’s Air Pollution Control Advisory Committee discussed a new draft regulation that air quality advocates hope could mitigate the impact of pollution on public health in the Mon Valley region, including the City of Clairton and McKeesport.

Jim Kelly, deputy director of environmental health at the health department, said in an interview that U.S. Steel has been cooperative early in the process that could lead to a new rule. U.S. Steel has representation on the county’s air pollution control committee.

U.S. Steel, which participated in the Dec. 8 meeting, said it is working to lessen the impact of inversions, noting the importance of predicting weather patterns that could trap emissions.

“We have committed to supporting Allegheny County Health Department’s development of a science-based model to better predict inversions and their intensity. We have also committed to doing our fair share to mitigate the effects of inversions on air quality to try to lessen the impact that inversions have in our communities,” Cox wrote. 

How would the new rule work? 

Companies would be required to submit an “air pollution watch plan” to the health department that includes procedures to ensure air pollution controls are properly working. During an air pollution watch, if the forecast predicts that the ambient concentration of fine particulate matter will exceed a threshold of 35 micrograms, companies like U.S. Steel would be required to ensure that staff is available to reduce emissions. 

If nevertheless the pollution stays above the threshold for 24 hours in a row and isn’t projected to change, the health department would issue an “air pollution warning,” which would trigger a company’s plan to reduce emissions.

The draft of the rule does not say how companies would have to reduce pollution or by how much. It does, however, require them to submit plans for how they will handle air pollution watches and warnings, which would need to be approved by the health department. 

“It’s up to us to evaluate if they’re reasonable,” Kelly said. 

Will the county take action if plans submitted by industry are considered insufficient? 

“We’ll cross that bridge when we get there,” Kelly said.

For air quality advocates, the draft rule is a step in the right direction — if industry takes it seriously.

We are happy to finally see the county revising their outdated episodic air regulations,”  Rachel Filippini, executive director of the Group Against Smog and Pollution [GASP], wrote in an email. “The initial draft we reviewed looks promising.”

Filippini, who is a member of the Air Pollution Control Advisory Committee, said “the proof will really be in the various measures industry will commit to undertake to reduce emissions of air contaminants to minimize the impact on public health.”

If approved by the subcommittee in the early months of 2021, the draft of the rule will need to go through a approval process via the Air Pollution Control Advisory Committee, the Board of Health, and eventually, the County Council. If contested by industry, the rule could also end up in court. A timeline has not been set.

James Bell is a PublicSource editorial intern. He can be reached at

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