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Air Pollution, Stench Pummels Mon Valley Over Holiday Period

Last week was one of excess for those in and around the Mon Valley, but not for the Thanksgiving-related reasons you might think: sadly, excess air pollution caused residents to grapple with abysmal air quality over the holiday break.


In summary, concentrations of fine particulate matter (PM2.5) exceeded national health-based standards at the Allegheny County Health Department (ACHD) air quality monitor in Liberty Borough three days in a row while levels of hydrogen sulfide (AKA H2S, that rotten egg odor you likely know all too well) exceeded the state standard six straight days.


For a less-quick, more-detailed recap, we need to go back a full week.


Air quality wasn’t great last Monday, and it got worse as the week proceeded. By Tuesday afternoon, both ACHD and the Pennsylvania Department of Environmental Protection (DEP) predicted air quality would continue this downward trend and shared their concerns publicly: ACHD issued a Mon Valley Air Pollution Watch, and DEP declared a Code Orange Air Quality Action Day for PM2.5 – both for Wednesday in the Mon Valley.


As a reminder, Mon Valley Air Pollution Watches and Warnings are issued as part of the county’s Mon Valley Air Pollution Episode Rule, which was designed to reduce PM2.5 levels during prolonged periods of poor air quality.

Under the new rule, ACHD staff monitor weather forecasts and atmospheric conditions that could lead to an “episode” (i.e., when meteorological conditions are likely to contribute to unacceptable air pollution levels in the Mon Valley for a day or more). A Watch is issued when these conditions are likely, and a Warning is issued when these conditions occur.

Early Wednesday, ACHD upgraded its Watch to a Warning, but that was a bit late by our calculations; PM2.5 crossed the “threshold” value necessary for a Warning around 10 p.m. Tuesday.

When ACHD issues a Warning – as it did last week and for a span of four days last month – sources of PM2.5 emissions within a defined Mon Valley area subject to the new rule are required to follow approved mitigation plans to reduce their emissions of particulate matter. We have a great explainer with info on the rule and all the facilities subject to it. You can check that out here.


Later on Wednesday – while those Warning plans were in place – ACHD extended its Mon Valley Warning into Thanksgiving and DEP declared a second Code Orange Air Quality Action Day for PM2.5 for the same day. ACHD again extended the Warning through Friday, and downgraded it to a Watch through Saturday - but by then the worst of the air quality has passed.


In the end, PM2.5 at ACHD’s monitor in Liberty Borough exceeded national health-based standards on Tuesday, Wednesday, and Thursday, but PM2.5 wasn’t the only pollutant of concern during this period of poor air quality: Levels of stinky old H2S exceeded Pennsylvania’s 24-hour average standard six straight days (from Tuesday through Sunday).


It’s also worth noting that concentrations of H2S exceeded PA’s 24-hour average standard on Wednesday at ACHD’s air quality monitor in Braddock Borough.


A quick word about H2S: It’s a colorless gas recognizable by its rotten egg odor and the concentrations we see 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.


This latest bout of poor air quality highlights two issues that we believe should be on ACHD’s to-do list:

  1. The department must examine the Mon Valley Air Pollution Episode Rule implementation to determine its effectiveness and ensure it protects public health.

  2. The department must do more to stop the onslaught of H2S exceedances in the Mon Valley. ACHD leaders have, in the past, treated H2S as a quality-of-life issue and downplayed its impact on the health and well-being of local residents. After six straight days of stench and H2S concentrations known to have health impacts, residents deserve better.

“We know that ACHD issued an enforcement order against U.S. Steel related to H2S violations at its Clairton Coke Works facility this past March, but what have they done since?” GASP Executive Director Patrick Campbell asked. “People who live and work in the Mon Valley and downwind of it need to know the people charged with protecting their health are being as proactive as possible to stem this ongoing issue.”


Editor’s Note: We will continue to keep an eye on the data and keep you posted. In the meantime, we graphed recent H2S and PM2.5 concentrations at the Liberty monitor for those who’d like to take a deeper dive into the data:







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