<UPDATED> More H2S Exceedances at Liberty, Mon Valley Residents Report Stench

Updated: Sep 9

Editor’s Note: This blog was updated at 10:35 a.m. Feb. 23 to include an updated H2S chart.

Users of CMU CreateLab’s crowd-sourcing app SmellPG reported the usual odors – saying the pungent air that seeped in through their windows last night and this morning was reminiscent of rotten eggs. Some said it was a strong sulfur smell. Others called it “industrial.”

The possible culprit could be the elevated concentrations of hydrogen sulfide that have pervaded the Mon Valley Monday and today. 


How bad has it been? Concentrations of H2S (known by its distinct rotten egg odor) at Allegheny County Health Department’s air quality monitor in Liberty Borough were so high today that by 9 a.m. an exceedance of Pennsylvania’s 24-hour average was already guaranteed.

There was also an exceedance at the Liberty monitor Monday – making it seven so far this year. While there have been no exceedances at ACHD’s air quality monitor in North Braddock yet in 2022, concentrations of H2S were just under that threshold both Sunday and Monday.


If you are unfamiliar with H2S, it’s important to note that exposure to low concentrations may cause irritation to the eyes, nose, or throat. It may also cause difficulty in breathing for some asthmatics. The EPA says exposure to low concentrations of hydrogen sulfide may also cause headaches, poor memory, tiredness, and balance problems. 


But H2S wasn’t the only air pollutant of concern Monday and today when PM2.5 concentrations were high enough to drive the AQI in the Liberty-Clairton area into the unhealthy ranges Monday.

Indeed, the AQI was high enough to land the area at the top of the list of places with the worst air quality in the United States. Levels of sulfur dioxide (SO2) were also elevated, with a peak one-hour value of 70 ppb Monday. 


By way of background: The 70 ppb level we saw yesterday wasn’t over any regulatory limit but it is the highest concentration of SO2 at Liberty we’ve seen since Dec. 26, 2019.


While GASP thanks ACHD for issuing an update on air quality, we hope they will consider being more proactive in the future and provide more health-based information to help residents mitigate their exposure to air pollutants.


“We hope they will consider adding information about these ongoing H2S exceedances that impact residents’ health and quality of life,” GASP Executive Director Patrick Campbell said. “Residents deserve to know what the officials charged with protecting their health are doing to address this issue.”

The Mon Valley is experiencing a weather inversion. The 24-hour rolling average at the Liberty monitor is between 50-100 on the Air Quality Index (AQI); we have not exceeded federal AQ standards and do not expect to, but the AQ team continues to closely monitor conditions. pic.twitter.com/QSdZV52aY4 — Allegheny County Health Department (@HealthAllegheny) February 22, 2022

GASP wants to note that today’s H2S exceedance was guaranteed mere hours before the Allegheny County Health Department’s public hearing regarding Clairton Coke’s draft operating permit.


For those who might not be aware: U.S. Steel’s Clairton Coke Works is a major emitter of H2S in Allegheny County.


While it’s too late to sign up to speak at tonight’s hearing, ACHD confirmed to GASP Monday that the event would be live-streamed on the department’s Facebook page.


GASP will be in attendance tonight to testify. Check back – we’ll post our comments and information from the hearing on our blog.

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