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Air Quality Exceedances Abound This Week at Allegheny County Health Department’s Liberty Monitor

Updated: Sep 9, 2022

The Allegheny County Health Department (ACHD) Tuesday morning issued a Mon Valley Air Pollution Warning for Tuesday and all of Wednesday. 

That, of course, meant that the rolling 24-hour average fine particulate matter (PM2.5) level at ACHD’s air quality monitor in Liberty borough exceeded the federal health-based standard *and* that ACHD is confident poor air quality is likely to continue. For those who might need a refresher on the Mon Valley Air Pollution Episode Rule, check out our FAQ here.

But PM2.5 wasn’t the only problematic pollutant this morning, nor was it the only one that exceeded regulatory limits.

Hourly monitor data show there was also an exceedance of the federal health-based sulfur dioxide (SO2) standard at Liberty. That standard requires SO2 levels to remain below 75 parts per billion (ppb).  So far this morning there were three hours over that limit, with the highest being 89 ppb.

In addition, concentrations of hydrogen sulfide (also known as H2S, which has a distinct rotten-egg stench) exceeded Pennsylvania’s 24-hour average standard at the Liberty monitor.  Today makes three days out of five air quality has exceeded the state standard: March 11, Monday (March 14), and today (March 15). There were also exceedances of the PA H2S standard on Monday and today at the North Braddock monitor.

This run of foul-smelling air comes on the heels of ACHD last week publishing a study that showed that years’ worth of H2S exceedances at the Liberty monitor were “entirely” caused by emissions from U.S. Steel’s Clairton Coke Works facility and later issuing an associated enforcement order complete with a $1.8 million fine.

“Air quality is just awful this morning,” GASP Executive Director Patrick Campbell said. “We’re grateful to ACHD for not hesitating to issue the Mon Valley Air Pollution Warning earlier, but we’re left wondering if any of the sources of the problem care what they are doing to their neighbors. This shouldn’t still be happening and it shouldn’t take regulatory intervention to force companies to consider their impact on public health.”

Editor’s Note: We graphed the H2S and PM2.5 data from the Liberty monitor- check it out:

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