The Biden-Harris administration introduced a proposal aimed at cutting nitrogen oxide (NOx) emissions from both new and existing gas-powered power plants, as well as other industrial facilities. However, this rule will not be finalized before President Trump assumes office. According to the Environmental Protection Agency (EPA) under Biden-Harris, the proposed regulation could lower nitrogen oxide emissions by up to 198 tons in 2027 and 2,659 tons by 2032. During his campaign, President-elect Trump pledged to roll back regulations to boost the economy and reduce costs in the electricity sector, but this new rule could lead to higher energy prices. Environmental groups intend to hold the Trump administration to a court-mandated deadline to finalize the rule by November 2025. A 2023 legal settlement between the EPA and environmental organizations that had sued the agency stipulates that the EPA must either strengthen the standards or formally decide against doing so by November 12, 2025. This appears to be a “sue and settle” lawsuit where a government agency agrees to a legal settlement from special interest groups, to create priorities and rules outside of the normal rulemaking process.
Nitrogen is a colorless, odorless gas that constitutes approximately 78% of the Earth’s atmosphere. During the combustion process—such as the burning of fuels at power plants—atmospheric nitrogen reacts with oxygen and water vapor to form various NOx compounds. The most significant of these is nitrogen dioxide, which contributes to the yellowish-brown color of photochemical smog. While only about 10% of nitrogen compounds in the air are due to human activities, the majority are produced by natural processes like the decomposition of organic matter. The formation of NOx is more influenced by the combustion conditions than by the type of fuel used. In addition to the nitrogen content of the fuel itself, the amount of nitrogen oxide formed is mainly determined by the temperature at which the combustion occurs.
The utility industry has made great strides in reducing nitrogen oxide emissions from power plants. Between 1989 and 2023, nitrogen oxide emissions from power plants have been reduced by 86 percent. As discussed below, nitrogen oxide is a criteria pollutant and is controlled by the Clean Air Act which sets a cap on how much nitrogen oxide emissions can be released into the atmosphere. Unlike other Biden-Harris EPA regulations such as the “power plant rule,” technology does exist to reduce NOx emissions, but adding that technology will raise costs for generators and consumers.
Control of Criteria Pollutants
The Clean Air Act mandates that the EPA establish National Ambient Air Quality Standards (NAAQS) to regulate pollutants deemed harmful to public health or the environment. These pollutants, known as “criteria pollutants,” include carbon monoxide, lead, sulfur dioxide (SO2), nitrogen oxides (NOx), ground-level ozone, and particulate matter (PM). They are referred to as “criteria” pollutants because the EPA sets the guidelines for their permissible levels, primarily to protect public health. Among these, SO2 and NOx are the main contributors to acid precipitation, commonly known as acid rain. When emitted into the atmosphere, SO2 and NOx react with water vapor and other airborne chemicals to form acids, which then fall back to the Earth as acid rain.
In 1971, EPA established New Source Performance Standards (NSPS) that provided allowable limits for NOx ranging from 0.2 pounds per million Btu to 0.8 pounds per million Btu, depending on the type of fuel burned and the combustion device used. The Clean Air Act was modified in 1990 and introduced a cap on the total amount of SO2 and NOx emissions that may be emitted by electric power plants nationwide. The primary goals of the Clean Air Act Amendments were a 10-million-ton reduction in SO2 emissions and a 2-million-ton reduction in NOx emissions from 1980 levels for electric generators. The compliance strategy employed is a cap-and-trade system, where electric utilities can buy permits from other utilities that have exceeded the required emission reductions under the cap. This approach allowed for more efficient decision-making regarding capital investments and construction timelines for utilities working to meet compliance standards. Additionally, utilities could reduce their emissions by installing environmental control technologies, such as Selective Catalytic Reduction (SCR), which is designed to remove nitrogen oxides (NOx) from exhaust gases.
Other rules also affect NOx emissions. The Cross-State Air Pollution Rule (CSAPR), for instance, requires 27 states to restrict emissions of sulfur dioxide and/or nitrogen oxide, which are precursors to the formation of fine particulate matter (PM2.5) and ozone. CSAPR establishes four distinct allowance trading programs for SO2 and NOx composed of different member states based upon the contribution of each state to downwind non-attainment of National Ambient Air Quality Standards.
Between 1970 and 2023, emissions from the six criteria pollutants declined by 78 percent even while economic indicators increased, including a tripling of GDP. The figure below shows increases in gross domestic product (321 percent), vehicle miles traveled (194 percent), energy consumption (42 percent) and population (63 percent) since 1970, and it compares them to the decline in the aggregate emissions of criteria pollutants of 78 percent. Today, we produce and consume more energy, drive further, and live more comfortably than we did in the past while enjoying a much cleaner environment.
The New Proposed Rule
The proposed New Source Performance Standards (NSPS) are based on the application of combustion controls and selective catalytic reduction (SCR). According to EPA, the proposed standards would ensure that new turbines built at natural gas-fired plants or industrial facilities, especially large ones, would be among the lowest-emitting turbines ever built.
According to Power Engineering, to strengthen the NOx performance standards for new stationary combustion turbines, EPA is specifically proposing:
- To determine that combustion controls with the addition of post-combustion SCR is the best system of emission reduction (BSER) for most combustion turbines. Post-combustion SCR is already widely used in the power sector.
- To lower the NOx standards of performance for affected sources based on the application of the BSER.
- To establish more protective NOx standards for affected new sources that plan to fire or co-fire hydrogen, ensuring that these units have the same level of control for NOx emissions as sources firing natural gas or non-natural gas fuels.
The proposed standards would establish size-based categories based on base load heat input that include:
- Large combustion turbines — facilities with a base load heat input rating of > 850 MMBtu/h (> ~ 85 MW).
- Medium combustion turbines — facilities with a base load heat input rating of > 250 and ≤ 850 MMBtu/h (> ~ 25 MW and ≤ ~ 85 MW).
- Small combustion turbines — facilities with a base load heat input rating of ≤ 250 MMBtu/h (≤ ~ 25 MW).
EPA is proposing to further subcategorize sources based on whether they operate at high, intermediate, or low loads, as well as whether they burn natural gas or non-natural gas fuels. When classifying low, intermediate, or base load units, EPA will consider the 12-calendar-month capacity factor of these combustion turbines.
- High load — capacity factor greater than 40% (i.e., base load).
- Intermediate load — capacity factor greater than 20% and less than or equal to 40%.
- Low load — capacity factor of less than or equal to 20%.
As Power Engineering notes, EPA acknowledged that SCR technology becomes less cost-effective and efficient at smaller scales or variable operating levels. Therefore, the agency is proposing standards for certain combustion turbines relying on combustion controls instead of SCR. This applies to small turbines at low or intermediate loads, and medium and large turbines at low loads.
EPA is accepting comments for 90 days after the proposal is published in the Federal Register.
Conclusion
The Biden-Harris EPA proposed to strengthen limits on nitrogen oxide emissions from most new and existing combustion turbines affecting natural gas power plants that will not be finalized by the time President-elect Trump takes office. This rule tightens new source performance standards for these plants. A 2023 legal agreement between the EPA and environmental groups that sued the agency requires the EPA to either tighten the standards or issue a formal decision not to do so no later than November 12, 2025. Trump campaigned on removing regulations not adding to them. This is yet another regulation that is being left for the incoming president by the Biden-Harris administration in fulfillment of Biden’s pledge to “end fossil fuels.”
