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. EPA has set standards for fine particles measured as PM2.5. PM2.5 means fine particles with a diameter of 2.5 micrometers and smaller, which is very small (the average human hair is about 70 micrometers in diameter – making it 30 times larger than the largest fine particle).
There are hundreds of types and sources of fine particles. Health effects are far from certain due to questions involving uncertainties of studies trying to link particle exposure to health effects via modeling, importance of different types of particles, and importance of exposures at low levels.
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 PM2.5. The power sector has reduced emissions of the SO2 and NOx “precursors” of PM2.5 by 91 and 82 percent, respectively, since 1990.
Air Quality Standards for PM2.5
The Clean Air Act (CAA) requires the U.S. Environmental Protection Agency (EPA) to establish national ambient air quality standards (NAAQS)—at levels that are protective of public health and welfare (environment)—for six pollutants, including PM2.5.
In 1997, the U.S. Environmental Protection Agency (EPA) revised the National Ambient Air Quality Standards (NAAQS) for particles to create new PM2.5 standards—15 micrograms per cubic meter for an annual average and 65 micrograms per cubic meter for a 24-hour average. In 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. EPA is supposed to evaluate whether to revise NAAQS every five years but the Agency is years behind its latest review and will not meet the December 2017 target.
Each tightening of the standard has consequences for state governments, businesses like electric companies, and the cost of many products and processes.
The Energy Industry is Reducing Emissions Related to PM2.5
The U.S. electric power sector has reduced air emissions substantially under existing programs. Since 1990, the industry has cut its two primary types of emissions that contribute to formation of particulate matter—sulfur dioxide (SO2) by 91 percent and nitrogen oxides (NOx) by 82 percent.
SO2 emissions reductions from electric utilities have been achieved by installation of control technologies as a result of environmental regulations such as the 1997, 2006 and 2012 PM2.5 NAAQS, the Acid Rain Program, the Clean Air Interstate Rule (CAIR), the Cross-State Air Pollution Rule (CSAPR), the Mercury and Air Toxics Standards (MATS) and regional haze requirements. The industry will achieve greater SO2 reductions in the future due to EPA visibility rules.
NOx reductions from electric companies have been achieved by installation of control technologies as a result of environmental regulations—such as the 1997 and 2008 ozone national ambient air quality standards (NAAQS); the 1997, 2006 and 2012 PM2.5 NAAQS; the Acid Rain Program; the “NOx SIP Call;" the Clean Air Interstate Rule (CAIR); the Cross-State Air Pollution Rule (CSAPR); the Mercury and Air Toxics Standards (MATS); and regional haze requirements. The industry will achieve greater NOx reductions in the future due to regulations like EPA's 2015 ozone NAAQS, the CSAPR Update rule and visibility rules.
In addition, advancements in clean fuels and renewables will continue to help the industry reduce SO2 and NOx emissions.