Very small, or fine, particles are released into the air around us—or are created—by emissions from many natural and manmade sources, including power plants. There are hundreds of types and sources of fine particles. While electric utilities typically remove more than 95 percent of direct fine particle emissions produced by their power plants, reactions in the atmosphere involving emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx) generate sulfates and nitrates, two of the many types of fine particulate matter (PM).
Air Quality Standards for PM
In 1997, the U.S. Environmental Protection Agency (EPA) revised the National Ambient Air Quality Standards (NAAQS) for particles to create new fine particle (PM2.5) standards—15 micrograms per cubic meter for an annual average and 65 micrograms per cubic meter for a 24-hour average.
In September 2006, EPA tightened the daily standard from 65 to 35 micrograms per cubic meter; however, EPA did not find compelling evidence to support a change to the annual standard of 15 micrograms per cubic meter.
In December 2012, EPA tightened the annual standard from 15 to 12 micrograms per cubic meter and established new monitoring requirements that will make the standard even stricter.
Power Plants are Reducing Emissions
The U.S. electric power sector has reduced air emissions substantially under existing programs. Since 1990, the industry has cut SO2 emissions by 79 percent and NOx emissions by 73 percent. The industry will achieve greater reductions over the next decade due to EPA and state regulations like EPA's Mercury, New NAAQS and Air Toxics Standards (MATS), the Clean Air Interstate Rule (CAIR)/Cross-State Air Pollution Rule (CSAPR) and visibility rules. EPA projects that SO2 emissions will be reduced by approximately 90 percent from 1990 to 2015.
Better Science is Needed to Set Appropriate PM Standards
Imposing stricter regulations for fine particulate matter will not necessarily produce additional health benefits beyond those achieved through the current standards, but will further exacerbate energy prices and prove burdensome to local economies. Even if it is assumed that current concentrations of fine particulate matter in the ambient air contribute to adverse health effects, it has not been established that emissions from power plants generate the particles of concern.