Mon Valley Has Been a Stench Fest - Here’s Why (And How to Take Action)

If you live, work, or play in or around the Mon Valley, we probably don’t need to tell you just how bad air quality has been over the past week or so. The Smell Pittsburgh app lit up with reports from or neighbors detailing everything from the way their community stunk (some described it as rotten eggs, while others deemed it industrial or chemical in nature) to the physical symptoms they experienced (sore throat, breathing difficulties, insomnia).

That distinct, nauseating odor is hydrogen sulfide (also known as H2S) and lately, it has reached levels that are impossible to ignore - levels that handily exceeded Pennsylvania’s 24-hour average standard. Over and over again.

In fact, there have been H2S exceedances every day for the past six days. Here’s a look at February so far (spoiler: more than 60 percent of the month so far has been in exceedance territory):

While the rotten egg smell is often the first thing we notice, the reality is way more than a nuisance. For residents in communities like Clairton, Liberty, Glassport, and Braddock, it’s a threat to peoples’ health and a persistent reminder of the air quality crisis in our backyard.

The Recent Spikes: What’s Happening?

In late January and early February 2026, air quality monitors in the Mon Valley recorded significant exceedances of Pennsylvania’s H2S standard. A combination of industrial emissions and weather inversions—where warm air traps pollutants close to the ground—created a perfect storm of toxic air.

GASP has been tracking H2S exceedances for YEARS, and despite Allegheny County Health Department enforcement actions and consent decrees, things have not gotten better. So far this year, there have been 22 H2S exceedances. During the same time period last year, there were just six.

For those asking, “But where does the H2S come from?” here’s what you need to know:

According to a 31-page study conducted by the Allegheny County Health Department, several years’ worth of H2S exceedances in the Mon Valley “can be attributed entirely to emissions from U.S. Steel’s Clairton coking facility.” 

Despite U.S. Steel scapegoating landfill facilities, we want to point out that the study also stated: “ACHD did not identify evidence of any other source contributing to the exceedances.”

What Now? Save the Date & Stand With Us

We are taking our concern directly to the decision-makers: The Allegheny County Board of Health. We want to let them know just how bad H2S has gotten so far this year, how it impacts residents, and how we can collectively work to stem these bad-air episodes once and for all.

And we hope you join us. Because YOUR story - your experience - matters. So, save the date for the next Allegheny County Board of Health meeting:

Date: Wednesday, March 18

Time: 12:30 p.m.

Place: Greater Pittsburgh Community Food Bank, 1 N. Linden Street, Duquesne, PA 15110

How you can help:'

1. Attend in person: Your presence is a powerful statement.

2. Sign up to speak: You must register at least 24 hours in advance to give public comment. Share your story of how the recent stench impacted your family.

3. Submit written comments: If you can't attend, ensure your voice is in the official record by submitting comments via the ACHD website.

Editor’s Note: Stay tuned, we will have more details closer to the Board of Health meeting date!