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UPDATED: ACHD Announces Monitoring Failure Led to H2S & Sulfur Dioxide Data Removal; GASP Seeking Further Info

UPDATE: ACHD monitoring staff got back to GASP Wednesday afternoon with an update. The department said that multiple municipalities via 911 had been receiving an especially high volume of complaints about sulfur-like odors in the Mon Valley over this period.

While the H2S concentrations were higher than usual during this time period, the instruments passed all quality assurance and quality control checks while the H2S data appeared to generally match the conditions we were receiving from the public. 

It was through evaluation of the data (especially as it relates to the ratio of SO2 to H2S) that an anomaly was spotted in the SO2 concentrations over this time period.  

They recommended folks take a look at the FAQ section ACHD developed, which will hopefully address those questions.

ACHD also noted that dates were being mulled for a subcommittee meeting, where the subject will be discussed at length. We will keep you posted on that meeting date when it's announced.


The Allegheny County Health Department (ACHD) announced in a press release Tuesday afternoon that hydrogen sulfide (H2S) and sulfur dioxide (SO2) data has been removed from the website after monitoring equipment at the Liberty Monitoring Station was discovered to be not fully functional.

The equipment failure impacts data from March 20, 2024, to May 14, 2024, and on May 17, 2024. ACHD stressed that only sulfur dioxide and hydrogen sulfide data were affected during this time period.

Here’s what the press release said:

The issue was discovered as part of the quality assessment and quality control process of the data. A probe line became dislodged from its exterior housing on the sulfur dioxide monitor causing readings to deviate from the norm despite the instrument passing all regular instrument quality assurance checks. 

No current enforcement actions are impacted by this data removal and the specific data affected during this time period will not be used in any future enforcement action(s). 

To learn more please visit the Hydrogen Sulfide webpage. For hourly data from all monitoring stations, including the Liberty Monitoring Station, visit the Hourly Air Quality Data.

“It’s concerning anytime there is an equipment failure that leads to data being invalidated,” GASP Executive Director Patrick Campbell said. “Given how much H2S emissions have impacted the area in general and Mon Valley residents in particular, we hope the health department releases more detailed information about what happened and what the ramifications might be.”

GASP on Wednesday morning reached out to ACHD monitoring staff to glean more information and to inquire about the date of the next Air Quality Monitoring Subcommittee meeting, where these issues are generally discussed in great detail. 

We will keep you posted on what we find out.

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