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Mild, mainly cloudy summer has kept smog levels at bay in Western Pennsylvania

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Thursday, Aug. 28, 2014, 11:12 p.m.

Pittsburgh-area residents can breathe a little easier this summer, because mild temperatures and heavy cloud cover reduced the number of days air quality dipped to a dangerous level.

There have been zero “Air Quality Action Days” in the Southwestern Pennsylvania region so far in 2014. Those are days in which ground-level ozone levels are high enough that the air is unhealthy to breathe, said Department of Environmental Protection spokeswoman Lisa Kasianowitz.

“We've had such a mild summer, there have not been a lot of days that have reached 90 (degrees),” she said. “You need sun and hot temperatures to form ozone from pollutants.”

Ground-level ozone occurs when pollution near the ground gets “baked” by sun and high temperatures to form ozone, also known as smog.

Average temperatures in July and August have been about 2 degrees lower than normal, said Brad Rehak, a meteorologist at the National Weather Service office in Moon. Forecasters expect this weekend to be warmer, with sun and predicted highs of 82 on Friday and 88 on Saturday, but Kasianowitz said DEP staff don't expect either would generate enough ozone to trigger an action day and break the region's streak.

The Liberty-Clairton area, which gets separate forecasts from the rest of the region because it's in the Monongahela River Valley and close to heavy industry, has had only one day this year (in February) in which particulate matter, or PM-2.5, has risen to trigger a DEP alert, Kasianowitz said.

The DEP issues a PM-2.5 alert when tiny pollution particles from engines and industry cling to moisture in the air and form a haze, Kasianowitz said.

“It's complicated, but we have been seeing a slow and steady decrease from the places with emissions that lead to ozone,” said Jamin Bogi, policy and outreach coordinator for the Group Against Smog and Pollution, a nonprofit air-quality advocacy group. “That trend is working in our favor.”

Improving vehicle emission standards and either shutting down coal power plants or reducing their emissions have helped to lower the levels of pollutants in the air that can form ozone.

James Fabisiak, an associate professor at the University of Pittsburgh's Department of Environmental and Occupational Health, said the weather helped reduce the number of action days, but he noted that people with breathing problems or weakened immune systems still could be at risk.

“Even the smallest doses we can measure still seem to have an effect,” Fabisiak said. “The risk decreases as the dose goes down, but we can't say there's a point where the risk is negligible.”

The Environmental Protection Agency uses a three-year average of air quality action days to measure a region's health. It is set to re-examine and possibly lower the threshold for ozone action days in the region, Bogi said.

“We're happy — this means healthier citizens, at least over the last few months,” he said. “We just have to keep our eyes on the ball.”

Matthew Santoni is a Trib Total Media staff writer. He can be reached at 412-380-5625 or

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