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Allegheny Co. Health Dept. Issues Mon Valley Air Pollution Warning as PM2.5 Concentrations Spike

Updated: Apr 16

Photo by GASP Board Member Roger Day

Editor’s Note: This blog was updated at 4:20 p.m. Nov. 7 to include additional information from the state Department of Environmental Protection.

Allegheny County Health Department (ACHD) Sunday morning issued a Mon Valley Air Pollution Warning, with preliminary data showing levels of fine particulate matter exceeded federal health-based air quality standards at its Liberty monitor. 

According to, the NowCast Air Quality Index (AQI) in the Mon Valley at one point Sunday morning soared to 175, which the Environmental Protection Agency (EPA) classifies as “unhealthy.” 

During periods of unhealthy air quality, the EPA suggests that people with heart or lung disease, older adults, children, and teens should avoid strenuous outdoor activities, keep outdoor activities short, and consider moving physical activities indoors or rescheduling them to reduce exposure to air pollutants.

In its Mon Valley Air Pollution Warning alert, ACHD told residents:

An Air Pollution Warning has been issued for the Mon Valley. The 24-hour PM2.5 standard for the Mon Valley has been exceeded at an official monitoring station in the Mon Valley and is likely to continue.Young children, the elderly, and those with respiratory problems, such as asthma, emphysema, and bronchitis, are especially vulnerable to the effects of air pollution and should limit outdoor activities during this time.
Companies contributing to pollution can contribute by temporarily reducing activities that produce emissions.More information about fine particulate matter (PM2.5), as well as the current monitored values can be found at:

But particle pollution wasn’t the only concern: Concentrations of hydrogen sulfide (H2S) at the Liberty monitor were also alarmingly high Sunday – so high that an exceedance of the state 24-hour average was guaranteed by 10 a.m. That makes 41 such exceedances at the Liberty monitor so far this year. There have been another 15 H2S exceedances at ACHD’s air quality monitor in North Braddock.

Conditions are predicted to improve today but could remain a concern through Tuesday, the extended forecast on offering an optimistic but inexact: “Good air quality may return by the mid-week period.”

The state Department of Environmental Protection on Sunday afternoon issued a Code Orange Air Quality Action Day for the Liberty-Clairton area Monday. You can get all the details on that here.

GASP will continue to monitor the data and will update this blog if/when new information is available.

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