Stagnant weather patterns in recent days have caused high air pollution levels in the southwest corner of Pennsylvania and nearly all of the eastern half of the state, prompting health concerns and the issuance of air quality alerts that more commonly occur in the summer.
The state Department of Environmental Protection has declared Air Quality Action Day alerts due to high concentrations of airborne particles over a broad swath of the eastern half of Pennsylvania this week, and predicted lesser but still elevated air pollution levels for Pittsburgh and the southwestern corner of the state.
Eric Shirk, a DEP spokesman, said the high pollution readings have been caused by a stationary front that has controlled the state's weather for most of the week.
"The winter tends to have much more wind, which prevents the stagnation of the often damp air," he said. "When there is less or no wind, as has been the case in the past several days, it allows the moisture and particulate matter to build to a level that warrants an Air Quality Action Day."
The state "action day" alerts, which advise at-risk residents of affected areas to limit outdoor activities, are based on the Air Quality Index, a daily measurement of ground-level ozone, airborne particles, sulfur dioxide, nitrogen oxides and carbon monoxide -- the five major air pollutants regulated by the federal Clean Air Act.
The U.S. Environmental Protection Agency established color codes to report daily air quality and make it easier for people to understand if air pollution is at unhealthy levels. Green means the air is good, yellow is satisfactory and orange means the air pollution level is "unhealthy for sensitive groups."
A code red reading, indicating an AQI of between 151 and 200, means conditions may be "unhealthy for everyone."
For the 8 a.m. hour Wednesday, pollution in the Liberty-Clairton region of the Mon Valley built to a code red AQI level of 157 -- the highest in the nation. Air quality also deteriorated into the code red range around Lancaster, Pa.
Philadelphia's AQI was in the 140s for much of the day, at the high end of the orange range, while Pittsburgh's topped out at 102.
Mr. Shirk said the late-in-the-year high pollutant levels are rare but not unprecedented. Action days with AQI in the orange zone due to airborne particulates occurred Dec. 1, 2012, in the Lehigh and Susquehanna valleys and in southeastern Allegheny County; and Oct. 25, 2012, and Nov. 13 and 14, 2010, in southeastern Allegheny County.
Jim Thompson, the Allegheny County Health Department's deputy director of environmental health, said that unlike most of the rest of the state, Allegheny County often has stagnant weather conditions in November and December when warmer fronts can cause air inversions in the region's river valleys and air pollutant levels can build.
"We had a very strong inversion in the Mon Valley [Wednesday] morning and that caused the reading in the red zone," said Mr. Thompson, who previously was the county's air program director. "It is an issue and it shows we still have some work to do on air quality."
According to a University of North Carolina study released in July, the deaths of 2.1 million people a year worldwide are attributable to surges in fine particulate matter air pollution. The tiny airborne particles can penetrate deep into human lungs and cause a variety of health problems, including asthma and other lung diseases, heart problems and cancer.
Weather forecasts indicate that a strong cold front will be moving into the state as the week progresses, with higher winds and much lower temperatures that should reduce air pollution levels.
Don Hopey: email@example.com or 412-263-1983.