The warnings about unhealthy air quality in the Monongahela Valley, which had been in effect since Saturday, were lifted Wednesday morning, the Allegheny County Health Department said.
“Overall atmospheric conditions have improved in the Mon Valley, and are expected to continue to do so moving forward,” the department said.
The warnings began Saturday when the department said the 24-hour standard for the pollutant PM2.5 had been exceeded at one of its monitoring stations in the Mon Valley, which is near U.S. Steel’s Clairton Coke Works.
The levels of PM2.5 often rise on chilly fall nights, when a weather phenomenon known as an inversion often occurs, trapping pollutants close to the ground.
PM2.5 is the term for fine particles that are a mixture of solids and liquid droplets in the air, with diameters of 2.5 micrometers and smaller. They can be inhaled and cause health problems, especially for young children, the elderly and those vulnerable to respiratory problems, such as asthma, emphysema and bronchitis. People with heart and lung diseases are considered sensitive groups.
The causes include power plants, motor vehicles, forest fires and industrial processes.
On Tuesday, the state Department of Environmental protection issued an “orange” alert in the Liberty-Clairton area. But by Wednesday morning, the county said, “The Air Quality Index is now reading within acceptable levels.”
Reports from the county’s air quality monitors are available on its website.
First Published: October 26, 2022, 1:02 p.m.
