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Same Old Story: More Rotten (Egg) Air Quality, Exceedances, in the Mon Valley

Updated: Mar 25

Ambient air concentrations of hydrogen sulfide (H2S) exceeded Pennsylvania’s 24-hour standard in North Braddock and Liberty on Wednesday according to Allegheny County Health Department (ACHD) air quality monitoring data.

Concentrations of H2S were so high in North Braddock that by 4:00 a.m. yesterday it was mathematically impossible *not* to exceed the 0.005 ppm standard, a figure that is averaged over an entire day. 

Although concentrations were down to 0.000 ppm for most of the afternoon Wednesday, overnight Tuesday into Wednesday morning concentrations of H2S were especially awful, averaging 0.035 ppm from 9 p.m. to 6 a.m.

Hydrogen sulfide is a colorless, flammable gas with a pungent, rotten egg odor that’s long been an issue for communities adjacent to and downwind of industrial sources like U.S. Steel’s Clairton Coke Works and Edgar Thomson facility.

“Most concerning may be the insane one-hour peak at the North Braddock monitor from 3 a.m. to 4 a.m. Wednesday of 0.077 ppm,” GASP Executive Director Rachel Filippini said.

For context: That peak is the third-highest one-hour H2S concentration ACHD has recorded in the past five years, according to preliminary Allegheny County Health Department air quality data.

Allegheny County’s first exceedance in 2021 of the 24-hour H2S standard occurred Feb. 21, after another instance where an extremely high one-hour H2S concentration at North Braddock – this time 0.071 ppm – followed by a few more bad hours drove the daily average to 0.010 ppm (twice the state standard).

“Two of the worst seven one-hour H2S concentrations recorded by the Allegheny County Health Department since January 2016 have occurred in the past 11 days,” noted GASP staff attorney Ned Mulcahy. “For some perspective, ACHD has reported over 44,000 hourly H2S readings during that period.”

These high values beg the question: What is happening in North Braddock to cause these issues?

ACHD only located an H2S monitor there in December 2020. The department did not offer its reasoning publicly for the addition but the announcement this past fall of increased monitoring around U.S. Steel’s Clairton Coke and Edgar Thomson facilities for hazardous air pollutants suggests that both moves reflect concern about emissions from those facilities.

Both of these developments were welcomed changes but a lack of transparency when it comes to enforcing air quality regulations and permit conditions continues to frustrate concerned residents.

“It’s bad enough that the public is still waiting to see if an enforcement action will be issued against U.S. Steel for high-profile emissions events this past summer at Edgar Thomson,” Filippini said. “But we are also waiting for a substantive public update regarding a compliance plan promised by the health department and the U.S. Environmental Protection Agency following a 2017 joint notice of violation.”

GASP calls on ACHD to investigate these short-term spikes in hydrogen sulfide and convey its findings to the public as soon as possible.

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