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Mon Valley Experiences Multi-Day Bad-Air Episode, Two More Air Quality Exceedances

Updated: Mar 28

It was a rough weekend of air quality for the Mon Valley, which experienced another days-long bad-air episode and two more air quality exceedances.

The Liberty-Clairton air shed – Clairton, Glassport, Liberty, Lincoln, and Port Vue – was regularly at the top of’s list of areas with the worst air quality in the nation over the past week, and was the subject of a state Department of Environmental Protection Agency (DEP) Code Orange Air Quality Action Day on Saturday.

An Air Quality Action Day is issued when the AQI is forecasted to be Code Orange or higher. On an Air Quality Action Day, young children, the elderly, and those with respiratory problems, such as asthma, emphysema, and bronchitis, are especially vulnerable to the effects of air pollution and should limit outdoor activities.

Additionally, the Allegheny County Health Department (ACHD) issued Mon Valley Air Pollution Watch alerts on Friday and Saturday. Mon Valley Air Pollution Watches are issued when the forecast indicates PM2.5 levels will likely exceed the 24-hour standard for the Mon Valley. 

More Air Quality Exceedances for Mon Valley

While PM2.5 levels ultimately did not exceed the 24-hour standard, concentrations of hydrogen-sulfide (AKA H2S, AKA a colorless gas most commonly recognized by its “rotten egg” odor) at the Liberty monitor did.

In fact, the average concentration of H2S exceeded Pennsylvania’s 24-hour standard of 0.005 ppm on both Friday, May 14 (0.009 ppm) and Saturday, May 15 (0.008 ppm) at the Liberty air quality monitor. Meanwhile, H2S at the North Braddock monitor did not exceed the 24-hour state standard but did come close – with concentrations of 0.005 ppm noted on Friday and Saturday, according to preliminary ACHD data.

For those keeping track, there have been 18 exceedances of the 24-hour H2S standard at the Liberty monitor so far this year, and nine at North Braddock.

U.S. Steel and Mon Valley Hydrogen-Sulfide Exceedances: What We Know

You hear about – and smell – H2S often, but where does it come from? Here in Allegheny County, mostly from U.S. Steel’s Clairton Coke Works. 

According to the DEP eFACTS website, U.S. Steel self-reported emitting roughly 155 tons of hydrogen sulfide from the Clairton Coke Works in 2019, the most recent year for which data is available. That makes it not only the number-one emitter of H2S in the county but also in the state.

GASP has long called on ACHD to track down the source of the county’s H2S problem, and on April 1 the department finally took action, issuing a Notice of Violation to U.S. Steel covering 25 exceedances that occurred in 2020 and seven in the first quarter of 2021 at the Liberty monitor. Eight exceedances of the state’s 24-hour H2S standard that occurred at the North Braddock monitor December 2020 through March 2021 were not included.

Procedurally, the notice is the first step for any enforcement action –  including civil penalties of up to $25,000 per violation per day – for air pollution sources. U.S. Steel had 14 days to schedule a meeting with ACHD to discuss the NOV before ACHD may proceed with further enforcement action. 

No further information about the notice or U.S. Steel’s response is available on the ACHD website. GASP submitted a formal Right to Know request to glean more information and will provide an update when that request is granted.

But What Was Up with Those Mon Valley Air Pollution Watches?

Mon Valley residents are likely familiar with DEP Code Orange Air Pollution Action Days, while Mon Valley Air Pollution Watches might be a new phenomenon. Here’s what you need to know:

Allegheny County Health Department worked for more than a year to craft episodic air pollution regulations that would require the ACHD Air Quality Program to issue Mon Valley Air Pollution alerts.  Those regulations are currently out for public comment and thus have not formally taken effect, but ACHD’s new language suggests that it is already preparing to implement them.

A “watch” would be issued when atmospheric conditions are expected to cause an exceedance of the national health-based standard for PM2.5 in any of the 32 municipalities in the affected area, with those conditions expected to last for another 24 hours. 

A “warning” would be issued once that standard has been exceeded and the weather forecast indicates that atmospheric conditions causing the exceedance are expected to persist for at least another 24 hours.

The regulations would require major and minor sources of fine particulate matter pollution like U.S. Steel to create and submit to ACHD for approval a two-tiered action plan to be implemented when these watches and warnings are issued. 

A “watch” plan must include procedures that ensure the source is “operating in a manner consistent with good engineering and all air pollution control equipment is maintained in good working condition.” 

During the warning phase, sources will be required to take certain actions to reduce their emissions. ACHD Air Quality Program officials said that could mean reducing transportation, switching or decreasing fuel use, delaying nonessential activities, or reducing, modifying or ceasing certain operations.

The regulations would also ban open burning on days where ACHD issues a Mon Valley Air Pollution watch or warning.

As we noted above, those regulations are out for public comment, and GASP’s legal staff is currently reviewing them – check back, we will have analysis and all the info residents need to formally weigh in on the new rules.

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