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UPDATE: PA’s 1-Hr H2S Standard Exceeded in Mon Valley for 1st Time Since ‘15; GASP Demands Answers

Updated: Oct 12, 2022

Editor's Note Update #2: The Allegheny County Health Department issued a follow-up public alert regarding hydrogen sulfide levels at the Liberty monitor. The message was sent through the Allegheny Alerts system at 11:31 a.m. Friday, Oct. 7.

"Our Liberty air monitor is continuing to register elevated levels of Hydrogen Sulfide (H2S). H2S levels declined during the day yesterday, but rose again overnight, surpassing the state nuisance limit. We expect levels to continue to decrease throughout the day with this afternoon’s projected forecast for rain. The Air Quality Program will continue to monitor the situation and provide updates as needed."

Update #1 Allegheny County Health Department issued the following update via social media and through its Alert system at 2:26 p.m. Thursday, Oct. 6:

The Liberty monitor has been reading high Hydrogen Sulfide (H2S) concentrations. A strong inversion started last night and broke at approximately 10:30 a.m. Weather conditions are expected to improve as the day continues. There is a chance of another inversion tonight. The Air Quality Program has been and will continue to monitor the situation and provide updates, as needed.

For up-to-date air monitoring information, please visit our online dashboard:

The odor of rotten eggs and industrial stench enveloped the Mon Valley Wednesday night and this morning, with users of the crowdsourcing app SmellPGH lamenting air quality they rated as “as bad as it gets” and describing physical symptoms like headache, difficulty breathing, and irritation of the eyes, nose, and throat.

The likely culprit is sky-high hydrogen sulfide concentrations at Allegheny County Health Department’s air quality monitor in Liberty Borough. ACHD monitor data show that H2S concentrations were so high that by 7 a.m., an exceedance of Pennsylvania’s 24-hour average standard was guaranteed.

That’s not all: On Wednesday evening, concentrations of H2S at the Liberty monitor exceeded Pennsylvania’s one-hour standard for the first time since 2015. For perspective, consider this: According to ACHD data, H2S levels this high have only occurred nine times in the past 20 years.

But let’s take a quick step back: Hydrogen sulfide (H2S for short) is a colorless gas recognizable by its rotten-egg odor. It’s a stench that those in the Mon Valley – and folks downwind of it – deal with all too often.

Exposure to the levels of hydrogen sulfide we see (all too often) in the Mon Valley can cause irritation to the eyes, nose, or throat as well as headaches, poor memory, tiredness, and balance problems. It may also cause difficulty in breathing for some asthmatics, according to the Agency for Toxic Substances and Disease Registry.

If you’re asking yourself at this point, “What is the source of all this H2S?” a recent ACHD study concluded it’s none other than U.S. Steel.

For those who might have missed it, the 31-page study found that years’ worth of H2S exceedances in the Mon Valley “can be attributed entirely to emissions from US Steel’s Clairton coking facility.”

Days after the study was published, ACHD issued a $1.8 million enforcement order against U.S. Steel over the H2S emissions issue. The company appealed the order and the case is ongoing.

Given this history, GASP today is again asking ACHD: Is there something going on at U.S. Steel’s Clairton Coke Works to cause these H2S values? Has the air quality program been in contact with the company?

“Residents deserve clean air to breathe. When they don’t get it, at the very least they deserve transparency and accountability from both ACHD and U.S. Steel,” GASP Executive Director Patrick Campbell said. “Residents need to know what’s causing the recent obscene H2S values and what’s being done to stem the issue.”

Editor’s Note: GASP has filed a formal air quality complaint and has reached out by email to ACHD staff for further information. We will keep you posted when - or if - we hear back.

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