Months after touting that all eight of its air quality monitors are in compliance with federal air quality standards for the first time ever, the county is again seeing spikes of incredibly dirty air — as recorded by the monitor today in Liberty across from U.S. Steel’s Clairton Coke Works.

In fact, levels of fine particulate matter (PM2.5) were elevated enough to give this spot the worst air quality in the country this morning, according to measurements at AirNow.gov. The Air Quality Index (AQI) — the EPA’s standard for reporting air quality — reached 153 on Wednesday morning, well into the red “unhealthy” zone.

The next-highest readings were in Portola, California, and Warner Robins, Georgia, with AQIs of 151. AQI readings below 100 are generally considered to be acceptable — those above 100 are considered unhealthy.

One nine separate days since the start of spring, the Liberty-Clairton area has been ranked among the top 10 places for worst air quality in the country, according to AirNow.gov.

Source: AIRNow.gov.

Fine particulate matter is a mixture of solids and liquid droplets that are only visible with an electron microscope. They consist of hundreds of different chemicals and can be inhaled. Some are created when they react to other pollutants in the atmosphere.

“The Health Department contacted U.S. Steel regarding these unhealthy air quality readings and was informed that they took their three oldest batteries offline sometime in the past 12 hours,” said the Allegheny County Health Department (ACHD) in a statement.

“We have requested that U.S. Steel delay bringing the batteries online until air quality improves and we have a better understanding of what caused the unhealthy situation.”

The ACHD is issuing an Air Pollution Watch for the Mon Valley for the next 24 hours, during which the PM2.5 levels will likely continue to exceed standards.

“It’s believed that much of the emissions are generated by the oldest and dirtiest batteries at Clairton,” says Rachel Filippini, executive director of  GASP, the Group Against Smog and Pollution. “That’s why the ACHD has asked them to not bring them back online. Those older batteries just have to be replaced permanently.

“The county is working on new coke oven regulations. Focusing on those oldest, dirtiest batteries seems like a very important place to start.”

Children, the elderly and those with respiratory problems such as asthma, emphysema and bronchitis are especially susceptible to air pollution and should limit outdoor activities for the moment.

Also, there’s that rotten egg smell again. For the second day in a row, concentrations of hydrogen sulfide (H2S) at the Liberty monitor surpassed the state’s 24-hour average standard of 0.005 ppm (parts per million), reaching 0.007 ppm, according to GASP.

The ACHD has recently hit U.S. Steel with $383,450 in fines for air quality violations. The penalties will go toward the Community Benefits Trust benefitting the Mon Valley communities of Port Vue, Lincoln, Liberty, Glassport and Clairton. Ten percent will go to the Allegheny County Clean Air Fund.

“Residents in [southwestern Pennsylvania] shouldn’t have to endure nine days of having the worst air quality in the country,” said Matt Mehalik, executive director of the Breathe Project, a Pittsburgh-based air quality advocacy group. “Yesterday 200 residents organized a town hall to demand that our elected leaders step up and address this ongoing health problem.”

GASP is circulating a petition to impose fees on major polluters, in order to sufficiently fund the ACHD’s Air Quality Program — an arrangement that is found in every Pennsylvania county but Allegheny.