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Mon Valley Again Experiences Worst Air Quality in the Nation, Exceedances Noted

Updated: Mar 25

Smell something foul in your neighborhood? If you live in the Mon Valley that’s probably a resounding, “YES.” Terrible air quality has plagued the area since Monday.

Concentrations of hydrogen sulfide (H2S) at the Allegheny County Health Department’s Liberty air quality monitor exceeded the state’s 24-hour standard on Monday with an average concentration of 0.006 ppm. The Pennsylvania limit is 0.005 ppm.

Two exceedances of that standard occurred on Tuesday, as well, – with concentrations of 0.008 ppm at the Liberty monitor and 0.012 ppm at the North Braddock monitor.

Overnight and into this morning Air Quality Index (AQI) soared into the red, unhealthy-for-all range, driven by concentrations of fine particulate matter (PM2.5). Preliminary data showed a peak from 5 a.m. to 6 a.m. of 125 ug/m3 and an average concentration of 76.1 ug/m3 from 9 p.m. Tuesday through today 6 a.m. today. The federal 24-hour standard for PM2.5 is 35 μg/m3.

“The Allegheny County Health Department must do a better job communicating these air quality matters to the public,” GASP Executive Director Rachel Filippini said. “Both Monday and Tuesday’s air dispersion reports said a moderate to strong morning surface inversion was expected. Yet, there was no alert about either the exceedances or the expected bad air.”

You may recall: Allegheny County’s first exceedance in 2021 of the 24-hour H2S standard occurred Feb. 21, after an extremely high one-hour H2S concentration at North followed by a few more bad hours drove the daily average to 0.010 ppm (twice the state standard).

A second exceedance occurred on March 3, following a similar pattern.

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