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Portions of the Mon Valley are under a 'Code Orange' air quality alert

In this May 2, 2019, file photo a worker arrives for his shift at the U.S. Steel Clairton Coke Works in Clairton, Pa.
Gene J. Puskar
In this May 2, 2019, file photo a worker arrives for his shift at the U.S. Steel Clairton Coke Works in Clairton, Pa.

With temperatures forecasted to climb into the 60s Tuesday, many are hoping to get outdoors. But the Pennsylvania Department of Environmental Protection is warning residents in the Liberty-Clairton area of Allegheny County to stay inside if they’re sensitive to air pollution.

The DEP has declared a Code Orange Air Quality Action Day for portions of the Mon Valley that include Clairton City, Glassport, Liberty, Lincoln, and Port Vue Boroughs Tuesday.

The air quality index in the region climbed to 126 by mid-morning, which puts conditions squarely in the middle of the “unhealthy for sensitive groups” category.

Those groups include those with respiratory conditions like asthma, emphysema and bronchitis as well as the very young and very old. The DEP called for those groups to limit outdoor activities Tuesday.

The high AQI is being credited to a temperature inversion — when a layer of warm air traps a layer of cool air and dust, smoke and other air pollutants — Tuesday morning, according to the DEP.

Companies most significantly contributing to particulate pollution in the Mon Valley region are required to temporarily reduce particulate emissions. A countywide rule established last September required companies to submit plans to the health department for how they would reduce those emissions.

U.S. Steel has not yet had a mitigation plan approved for its Clairton plant, according to the county’s website. The plant often draws criticism from environmental groups for its role as a major source of particulate matter pollution and other pollutants. It accounts for 93% of all reported hydrogen sulfide emissions in Allegheny County, and 72% of all emissions of hydrogen sulfide in the state.

The Allegheny County Health Department said an air pollution warning will continue through Wednesday as levels of fine particulate matter are expected to continue to exceed federal standards.

“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,” a statement from the health department reads.

The state DEP is encouraging residents and businesses to help reduce air pollution by avoiding open burning of leaves, trash and other materials and not using gas-powered lawn and garden equipment and fireplaces and wood stoves.

Kiley Koscinski covers city government, policy and how Pittsburghers engage with city services. She also works as a fill-in host for All Things Considered. Kiley has previously served as a producer on The Confluence and Morning Edition.