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UPDATED: Several More H2S Exceedances for Mon Valley as Poor Air Quality Lingers

Updated: Mar 25

Editor’s Note: This story was updated at 3:51 p.m. Monday to include today’s exceedances at the Liberty and North Braddock air quality monitors.

High concentrations of hydrogen sulfide (H2S) in the Mon Valley led to exceedances of the state standard on Saturday and Monday at the Allegheny County Health Department’s air quality monitoring sites in Liberty and North Braddock.

For the uninitiated: Hydrogen sulfide is a colorless gas most commonly recognized by its “rotten egg” smell.

The most recent spate of bad air came just days after ACHD issued a notice of violation to U.S. Steel’s Clairton Coke Works facility addressing 32 exceedances of the state’s 24-hour average H2S standard that occurred Jan. 2020 through March 2021 in Liberty. The notice precedes any potential enforcement action, which here could include civil penalties of up to $25,000 per violation per day.

Worth noting is that this notice did not address eight exceedances of the H2S standard that occurred in North Braddock from Dec. 2020 through March 2021.

While air quality was fair Sunday, the AQI soared into the red early Monday morning in Clairton, meaning “some members of the general public may experience health effects” and that “members of sensitive groups may experience more serious health effects.” At one point, the Liberty-Clairton area had the second-worst air quality in the nation according to

The level of fine particle pollution in the Mon Valley was especially concerning early Monday, where PM2.5 surged to 99 ug/m3 from 7 a.m. to 8 a.m. at the Liberty monitor. By contrast, PM2.5 levels at ACHD’s other monitors (along the Parkway East and in Avalon and Lawrenceville) showed levels no higher than 17 ug/m3.

In fact, ACHD on Monday morning sounded the alarm, tweeting out a series of messages warning the Mon Valley about elevated levels of PM2.5.

“We thank the health department for communicating today’s poor air quality to folks in the Mon Valley via social media,” GASP Executive Director Rachel Filippini said. “GASP and others are actively working with ACHD to increase and improve these types of communications and we look forward to more robust messaging in the future.”

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