Recent concentrations of fine particulate and ground level ozone air pollution follow a familiar trend. Both are improving, the most recent federal single-year data suggest. But only ozone meets health-based air quality standards when longer-term levels are considered.
The 8-hour annual average for ozone in southwestern Pennsylvania fell to .073 parts per million in 2016, slightly lower than in the previous year, according the most recent year-over-year data reported by the U.S. Environmental Protection Agency.
Moreover, single-year data masks the fact that the three-year average of ozone levels in the region meets the .070 parts per million standard set under the Clean Air Act.
Fine particulate pollution known as PM2.5 is a different story. Levels in the region have fallen significantly in the 21st Century. But Allegheny County, the region’s urban core, is still shy of meeting the 12 micrograms per cubic meter annual federal standard based on a three-year average of pollution levels.
Six widespread air pollutants are regulated by the National Ambient Air Quality Standards under the Clean Air Act. Ground-level ozone is one of them.
Ozone can travel hundreds of miles and, when breathed, harm lung tissue, reduce lung function and worsen bronchitis, emphysema and asthma. The gas is caused by a reaction of sunlight and the vapors emitted when fuel is burned.
Annual levels have fallen 17 percent across the region since 2000. “We’ve had improvement in automobiles and better controls on power plants,” said Jayme Graham, Allegheny County Air Quality Program chief. “Those are the two major sources of the pollutants that create ozone.”
Single-year data show that Allegheny and Washington counties experienced declining ozone levels in 2016, while average concentrations rose in Armstrong, Washington and Westmoreland counties the same year.
The region has been in compliance with the 8-hour annual ozone standard for two consecutive years. Compliance is based on whether the three-year average ozone concentration in a region is at or below the .070 parts per million standard. The region’s average annual ozone level was .070 in the 2014-2016 period, the most recent for which data are available.
The microscopic size of PM2.5 enables the particles to evade the body’s natural defenses and travel deep into the lung and blood stream, making them particularly dangerous. The pollutant has long been a problem in southwestern Pennsylvania, where industrial plants in pollution-trapping river valleys are major contributors.
Single-year PM2.5 data show the levels of the pollutant decreased in the Pittsburgh region slightly to 12.8 micrograms per cubic meter of air in 2016. Fine particulates were lower in every county in the region except Westmoreland. Still, meeting federal PM2.5 standards first enforced in 1997 remains elusive.
The 2016 annual PM2.5 average for the Pittsburgh area is the highest single-year level among 16 Pittsburgh Today benchmark regions. It represents the greatest concentration recorded in the Pittsburgh region. In 2016, that reading was taken at the Liberty Borough monitor in Allegheny County, which records the air quality in the industrial corridor downwind of the US Steel Clairton coke plant along the Monongahela River.
Recent data suggest PM2.5 levels are higher than the 2013 annual average of 12 micrograms per cubic meter in Allegheny County. But understanding the trend is complicated. A previous lab issue resulted in some data being invalidated. In such cases, the EPA requires that those data be substituted with the highest levels recorded over the previous five years. “The values are not going up because pollution is worse,” said Jim Kelly, Allegheny County Health Department deputy director, who oversees the Bureau of Environmental Health. “They’re up because we had to use data substitution procedures to make up lost data.”
Annual PM2.5 concentrations in the Mon Valley corridor have fallen 42 percent since 2000 as a result of economic conditions, regulation, advocacy, enforcement, technological advances and industry investment, including more than $600 million in upgrades at the Clairton plant. Yet, it remains one of the most polluted corridors in the nation.
Under a recent consent decree, US Steel agreed to make additional upgrades and take other steps at the Clairton plant to lower emissions. “We’re already seeing some improvement,” Graham said. “We think it will help a great deal not only with particulates, but also the hydrogen sulfide smells people have been getting.”