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UPDATED | Watchdog Report: Two More Air Quality Exceedances for Mon Valley

Updated: Mar 25

This story was updated at 3:28 p.m. April 8 to include information released by the Allegheny County Health Department via the Allegheny Alerts system. Not subscribed yet? You can sign up to receive them here.

Allegheny County tallied two more air quality exceedances Wednesday – one for hydrogen-sulfide (H2S) and the other for fine particulate matter (PM2.5).

The 24-hour average PM2.5 concentration at Allegheny County Health Department’s air quality monitor in Liberty yesterday was 38.2 ug/m3, exceeding the national health-based standard of 35 ug/m3.  

For those keeping track: This is the second such exceedance so far in 2021, though both are based on preliminary data. The previous exceedance was March 10 (44.6 ug/m3).

The 24-hour average H2S concentration at Liberty Wednesday was 0.009 ppm, nearly twice the state standard. 

That means there have been exceedances four out of five days at Liberty – 10 in the past 31 days.

The latest bout of bad air quality prompted the health department to issue a Mon Valley Watch. In an Allegheny Alert message, ACHD told residents that officials had been in contact with U.S. Steel regarding unhealthy air quality readings and was informed that the company took its three oldest batteries offline. ACHD is requesting additional information from the company to understand the situation.

ACHD on Thursday afternoon provided an update to the public regarding the recent bout of bad air:

This morning’s PM2.5 values at all monitors are in the moderate range.The Allegheny County Health Department had significant communication with US Steel yesterday and is also looking at all other sources of emissions that could have been responsible for the elevated readings Tuesday evening.
The preliminary monitoring data indicates that the high overnight levels of fine particulate matter (PM2.5) contributed to an exceedance of the 24-hour Federal health standard.More information about fine particulate matter (PM2.5), as well as the current monitored values can be found at:

GASP is following the issue – check back for more updates.

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