Ground-level ozone is created by chemical reactions between emissions of nitrogen oxides (NOx) and volatile organic compounds (VOCs) in the presence of sunlight.

Motor vehicles, industrial facilities, electric companies, construction equipment, locomotives and ships are some of the major sources of NOx and VOCs. Currently, electric companies emit only about 5 percent of the nation’s combined emissions of NOx and VOCs.  The power sector has reduced emissions of the NOx “precursor” to ozone by 88 percent since 1990.​

Air Quality Standards for Ozone

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 ozone.
EPA reviewed its ozone standards in 1997 and set a tighter limit of 0.08 parts per million (ppm) for a new measuring time period, the 8-hour average (with rounding, the standard actually was 0.084). The CAA requires EPA to complete a review of each NAAQS, including ozone, at five-year intervals and make any necessary revisions. In 2008, EPA tightened the standard again to 0.075 ppm and in 2015 the Agency further lowered the ozone NAAQS to 0.070 ppm. In December 2020, EPA retained the 2015 standards.​

The Energy Industry is Reducing NOx Emissions that Help to Reduce Ozone

The electric power industry nationally has reduced its national total NOx emissions by 88 percent since 1990. NOx emissions are one of two man-made chemicals that contribute to ozone formation; electric power sources emit very little of the other, called volatile organic compounds (VOCs) or hydrocarbons. NOx reductions from electric companies have been achieved by installation of control technologies as a result of environmental regulations – such as the ozone NAAQS; the 2012 and earlier fine particulate matter NAAQS; the Acid Rain Program; the “NOx SIP Call;" the Clean Air Interstate Rule (CAIR); the Cross-State Air Pollution Rule (CSAPR) and CSAPR Update; the Mercury and Air Toxics Standards (MATS); and regional haze requirements – and advancements in clean fuels and renewables.
The industry will achieve greater NOx reductions in the future due to new regulations, using cleaner fuels, and increased electric generation from renewables like solar and wind.


Learn more at EPA’s Ozone site.