Another Abysmal Air Quality Day in Mon Valley: Fine Particulates *AND* H2S Elevated Today

Updated: Oct 12

On what otherwise is a beautiful fall day for many residents of southwest Pennsylvania, air quality in the Mon Valley is abysmal Tuesday, the details of which can best be described as bad news and worse news.


First, the stench continues: concentrations of hydrogen sulfide (AKA H2S, AKA that rotten egg odor folks in the Mon Valley are all too familiar with) remain elevated at the Allegheny County Health Department (ACHD) air quality monitor in Liberty Borough.


Second, the Pennsylvania Department of Environmental Protection (DEP) on Monday declared today a Code Orange Air Quality Action Day for fine particulate matter (or PM2.5) and the ACHD issued a Mon Valley Air Pollution Watch, which is also based on predicted high PM2.5 levels.


It’s been a rough week of air quality for our friends in the Mon Valley - especially when it comes to H2S – and we know adding PM2.5 into the mix means there’s a lot to unpack. So let’s get some important background info out of the way (especially for those who might just be tuning in).


Tuesday marks the third day in a row that the Mon Valley was overwhelmed with stench. By 8 a.m. this morning, an exceedance of the state’s 24-hour average standard was guaranteed. It’s the sixth such exceedance at the Liberty monitor in the past seven days.


The odor was bad this morning, but H2S levels were not the worst of this episode: Last week concentrations of H2S exceeded Pennsylvania’s one-hour standard for the first time since 2015. H2S levels exceeding the state 1-hour standard have only occurred nine times in the past 20 years, according to ACHD monitor data.


While ACHD’s public messaging last week referred to the H2S issue as a “nuisance,” GASP remains concerned about the very real public health impacts. We know that exposure to the levels of H2S often seen 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.

As if that wasn’t enough of a (potentially literal) headache, for the first time in this wave of poor air quality PM2.5 is also a problem.

When DEP issued its Code Orange Air Quality Action Day warning yesterday, that meant officials expected the full day today to end up as an “orange” air quality index (AQI) day. As a reminder, the Environmental Protection Agency (EPA) uses a color-coded system to classify the severity of air quality. AQI values in the “red” range mean air quality is “unhealthy” and that “members of the general public may experience [adverse] health effects,” while the “orange” range means air quality is “unhealthy for sensitive [populations]” like children and folks with respiratory diseases. You can learn more about that here.

The lowest “orange” AQI is 101 and equates to a 24-hour PM2.5 average of 35.5 ug/m3 - which is an exceedance of the National Ambient Air Quality Standards. While we can’t say for sure - yet- that there will be such an exceedance at the Liberty monitor today, ACHD air quality data show we are on track for one.

What we *can* say for sure is that as of 8 a.m. today, PM2.5 levels hit the Mon Valley Air Pollution Episode Rule threshold. That means that ACHD could have - and we think should have - upgraded its Monday Watch to a Warning, assuming “the Department has determined atmospheric conditions will continue” to contribute to poor air quality.

A “Mon Valley Air Pollution Warning” would have required source of particulate matter emissions to take “measures to reduce PM2.5 and PM10 emissions to minimize the impact on public health, safety, or welfare.”

Unfortunately, since issuing the Mon Valley Air Pollution Watch yesterday afternoon, ACHD has done no further outreach through its Allegheny Alerts system or social media channels to remind residents of unhealthy air quality and how to mitigate exposure.

“Real people are suffering, and they need to be able to trust that the health department is going to arm them with all the information and resources they need to make informed decisions when air quality is unhealthy,” GASP Executive Director Patrick Campbell said. “We have real concerns about how the Mon Valley Air Pollution Rule is being implemented and think it’s time ACHD revisit the rules to make them more protective of public health.”

Editor’s Note: Here’s how to file an air quality complaint with Allegheny County Health Department. And here’s our Resident’s Guide to the Mon Valley Air Pollution Rule and the facilities subject to it. Also: We graphed the PM2.5 and H2S values for those who'd like to take a deeper dive into the air quality data. Check it out:



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