Air pollution warning issued for Mon Valley

The Allegheny County Health Department issued a weekend air pollution warning Saturday for the Mon Valley.

It said the 24-hour standard for the pollutant PM2.5 had been exceeded at one of its monitoring stations in the Mon Valley and will continue into Sunday.

PM2.5 is the term for fine inhalable particles, which are a mixture of solids and liquid droplets found in the air, with diameters that are generally 2.5 micrometers and smaller.

To get a sense of how small 2.5 micrometers is, the Environmental Protection Agency compares it to the scale of a human hair. It says the average human hair is about 70 micrometers in diameter — making it 30 times larger than the largest fine particle.

That’s small enough to get deep inside people’s lungs, and possibly even the bloodstream, causing health problems.

According to the EPA, “some are emitted directly from a source, such as construction sites, unpaved roads, fields, smokestacks or fires. Most particles form in the atmosphere as a result of complex reactions of chemicals such as sulfur dioxide and nitrogen oxides, which are pollutants emitted from power plants, industries and automobiles.”

The county’s alert noted: “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.”

It said that companies most significantly contributingto particulate pollution in the Mon Valley region are required to temporarily reduce particulate emissions.

There have been several reports of air quality issues in the region this month, includinga Code Orange alert from the Department of Environmental Protection on Oct. 10 and reports of hydrogen sulfide levels above the state standard.

At this time of year, the region is prone to weather inversions, which occur when a layer of warmer air traps pollution close to the ground. This often happens overnight during chilly autumn weather.

Reports from the county’s air quality monitors are available on its websiteat https://www.alleghenycounty.us/HealthDepartment/Programs/ Air-Quality/Air-Quality.