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Unhealthy Air, Stench Return as Mon Valley Sees 5th H2S Exceedance of Year, GASP Calls for Answers

Updated: Sep 9, 2022

Wednesday marked the fifth time so far this year that levels of hydrogen sulfide (AKA H2S, an air pollutant distinguished by its rotten-egg odor) exceeded the state’s 24-hour average standard at Allegheny County Health Department’s air quality monitor in Liberty Borough. 

Preliminary data also show that while concentrations of H2S were also elevated at ACHD’s air quality monitor in North Braddock, the 24-hour average was close to – but just short of – an exceedance.

Local residents confronted by yesterday’s stench took to CMU CreateLab’s SmellPgh app to detail how industrial and rotten-egg odors were potent enough to seep in through their closed windows and wake them from sleep. 

They also described physical symptoms like sore throats, asthma flareups, headaches, nausea, congestion, and more.

But H2S wasn’t the only pollutant impacting the Mon Valley yesterday: Concentrations of fine particulate matter, a harmful air pollutant known as PM2.5 were also elevated during the early part of the day – contributing to an Air Quality Index (AQI) that the Environmental Protection Agency (EPA) classifies as unhealthy for everyone. 

For several hours Wednesday, the Liberty-Clairton’s AQI was the worst in the country (again), according to’s NowCast:

(Quick aside: Fine particulate pollution is harmful to human health because it’s smaller and more able to infiltrate the body through the nose, mouth, and skin. This means they can travel deep into the lungs and even into the bloodstream. PM2.5 is linked to heart attacks, strokes, arrhythmias, and lung cancers. Exposure to PM2.5 is also linked to everything from baldness to dementia to mental illness.)

“While concentrations of fine particulate matter were concerning but didn’t rise to the levels of triggering a Mon Valley Air Pollution Warning, yesterday was still a rough one for many residents in the Mon Valley because of poor air quality,” GASP Executive Director Patrick Campbell said. “A quick look at the SmellPgh app shows there was a short-term air pollution episode occurring that was impacting people’s health and quality of life. We think on these days, residents should be able to expect communications from the public health officials charged with helping protect their – our – wellbeing. But ACHD leadership again failed in this regard.”

While no communications were issued regarding the abysmal air quality, ACHD did post an air dispersion forecast that indicated residents could expect AQI in the healthy range, warning only that “PM2.5 concentrations will be highest in the morning hours.”

“We’re concerned about the disparity between what ACHD forecasted and included in its report and what residents actually experienced,” Campbell said. “GASP hopes that health department leaders see yesterday’s poor air episode as we do: A powerful example of why residents and advocates like GASP have been requesting more health-based information during these short-term periods of unhealthy air quality that do not rise to the occasion of a Mon Valley Watch or Warning.”

So GASP is again asking ACHD Chief Operating Officer Patrick Dowd and his leadership team at the health department to better communicate with residents during these types of air pollution episodes that threaten public health but do not meet the criteria for a Mon Valley Air Pollution Episode alert and address the ongoing H2S exceedances.

Editor’s Note: H2S concentrations at the Liberty monitor exceeded the Pennsylvania 24-hour average standard 54 times last year – which was more than twice 2020’s numbers. Here’s a chart detailing the H2S exceedances so far this year:

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