Science Policy & Funding Opinion

Affordable Clean Energy Rule Threatens Progress of Clean Air Act

The scientific community must act to minimize the adverse air quality and health impacts of relaxed EPA regulation.

By and Melissa Fiffer

Last year, the U.S. EPA finalized the Affordable Clean Energy (ACE) rule, a dramatic relaxing in air pollution standards. ACE effectively rolls back the Obama administration’s Clean Power Plan (CPP), policy that aimed to reduce carbon emissions from U.S. electrical power generation—in particular, from coal-burning power plants—through the first national standards. ACE instead allows states to decide their own standards and makes major changes to the way the EPA calculates the health risks of air pollution.

As an atmospheric scientist in Maryland focused on air pollution and a policy wonk turned environmental epidemiologist, we argue that ACE does not adequately address the emission reductions needed in the United States and that it is imperative the government address the serious air quality–related repercussions it will have on public health.

Better Than Nothing Is Not Good Enough

The Clean Air Act was the first comprehensive federal law regulating air pollution emissions. In Massachusetts v. EPA, the U.S. Supreme Court found in 2007 that the EPA has statutory authority and is, in fact, required by the Clean Air Act to regulate greenhouse gases, including carbon dioxide (CO2). That’s the precedent under which 22 states and seven cities are suing the EPA in federal appeals court, asserting that ACE fails to take the necessary steps to regulate greenhouse gas emissions.

Although ACE is projected to decrease emissions of CO2 and copollutants compared to no action, ACE and the CPP differ dramatically in the magnitude of reduction they would achieve. According to the EPA, the CPP would have reduced CO2 emissions by 415 million tons by 2030, whereas the ACE rule is projected to reduce emissions by 11 million tons. That amounts to a 0.7% contribution to overall reduction, with much of the decrease due to ongoing market and industry trends. Compared to the CPP, the ACE rule will allow an increase of CO2 emissions by 3% and sulfur dioxide (SO2) and nitrogen oxide (NOx) emissions by 5%–6% by 2030, although these increases are challenging to estimate because of the range of measures that states might apply.

The weaker emission reductions under ACE are due to the rule’s far less stringent control strategies. All emission policies like ACE and CPP are required under Section 111(d) of the Clean Air Act to establish the “best system of emission reduction” for the pollutant and the source. Under ACE, that system is defined as heat rate improvements (HRI), essentially energy efficiency measures, at coal-fired electricity-generating units. By contrast, the CPP established a set of emission reduction measures, including utilizing lower-emitting natural gas units and transitioning from fossil fuels to renewable energy, in addition to the energy efficiency measures included in ACE. When establishing ACE, the EPA argued that the CPP exceeded the agency’s authority to define the best system of emission reduction.

This limited approach may also result in increased SO2 and NOx emissions through a phenomenon known as the rebound effect. If coal power plants become more efficient through HRI investments, dependence on coal-generated power could rise, increasing emissions overall [Keyes et al., 2019].

A Problem Downwind

Coal power generation has been on the decline in the United States, a trend the COVID-19 pandemic has accelerated. The coal plants still in operation are running at lower capacity—some at just 30% to 40%. But because those plants are producing less energy and thus fewer emissions overall, they don’t need to use pollution control measures to meet annual caps. Modern technologies can remove 80% to 90% of the NOx and SO2 under optimized conditions; however, about 30% of the nation’s coal-burning power plants do not have scrubbers, and 22% do not have advanced nitrogen controls.

Maryland is one state that has substantially reduced its production of emissions, as a result of the Greenhouse Gas Emissions Reduction Act of 2009 and its membership in the Regional Greenhouse Gas Initiative. Yet in 2016, the state of Maryland filed a 126 Petition to the EPA arguing it could not meet its own state standards for air quality because of coal plants in Indiana, Kentucky, Ohio, Pennsylvania, and West Virginia that were not using pollution control technologies. ACE’s allowance for states to create their own emission standards may further exacerbate air quality nonattainment concerns in downwind states.

Health Consequences of ACE

The increase in emissions that ACE will allow translates into significant public health impacts. Even the analysis of the rule does not treat these impacts adequately. When ACE was proposed in 2017, an initial analysis of the new rule used the existing CPP and its more stringent standards as a baseline scenario. By the time the rule was finalized in June 2019, new analyses compared ACE to a world that wasn’t implementing the CPP.

Accordingly, the initial analysis showed that ACE would increase premature deaths by 470–1,400 and asthma attacks by 48,000 in the United States by 2030, whereas the final analysis found a modest reduction in premature deaths (50–122) and asthma attacks (14,000). For context, the CPP would have prevented 3,600 premature deaths and 90,000 asthma attacks each year, making the final ACE rule pale in comparison. Given the pushback that EPA received about the projected increases in premature deaths cited in the initial analysis, the change in baseline approaches is likely an effort to conceal scientific evidence.

The projected health impacts are based on established environmental epidemiology literature linking fine particulate matter (PM2.5) and ozone exposure to adverse respiratory and cardiovascular outcomes. The EPA did not quantify the health effects associated with changes in emissions of SO2, NOx, and mercury, which include asthma cases, emergency room visits, and damage to the developing nervous system [e.g., Kampa and Castanas, 2008]. If these effects were taken into account, the public health toll of the ACE rule would rise even higher.

An architect of ACE (and former coal industry lobbyist) has said the “collateral effects” of the rule on copollutant levels can be addressed through established regulations under the Clean Air Act, such as criteria air pollutant reviews. However, the EPA’s own actions demonstrate how adamant the agency is about doing just the opposite. The Strengthening Transparency in Regulatory Science rule would discount studies that rely on confidential health information. If finalized, the EPA would devalue research that forms the basis for criteria air quality standards unless the personal medical records used in the study were made public.

The EPA has also undermined its own authority to regulate hazardous air pollutants under the Mercury and Air Toxics Standards by determining that it is neither appropriate nor necessary to regulate mercury emissions from power plants. Further, the EPA recently proposed to maintain the PM2.5 standard, contrary to advice from independent scientists, who were intentionally excluded from the rule-making process. The timing could not be worse, as early research indicates counties with a 1-unit increase in long-term PM2.5 exposure suffer 8% higher COVID-19 death rates. (In light of the long history of racial and ethnic injustices in U.S. pollution levels and the fact that Black Americans are dying from COVID-19 at more than twice the rate of white Americans, a new study will assess whether air quality disparities contribute to increased COVID risks among communities of color.)

Scientists and the Public Need to Insist on Science-Based Policy

The ACE rule is part of a larger effort to relax and reinterpret Clean Air Act standards that will hamper the effectiveness of future policies to protect human health. As scientists, we understand the importance of providing accurate and reliable information to inform decisionmaking. However, the purposeful tactics to misguide the public, including changing the way costs and benefits are balanced, removing experts from EPA advisory boards, and ignoring the health benefits of reducing pollution, will have substantial consequences for future EPA operations.

We call on the science community and all U.S. residents to hold the EPA to a better standard. Check the docket regularly to monitor proposed EPA actions and comment whenever possible. Seek opportunities to partner with state policymakers who are pushing back against unfounded EPA rules. Vote for government representatives who care about the health of their constituencies. And insist that the agency with authority to keep our air clean and breathable commit to environmental rule making anchored in the best available science.


Kampa, M., and E. Castanas (2008), Human health effects of air pollution, Environ. Pollut., 151(2), 362–367,

Keyes, A. T., et al. (2019), The Affordable Clean Energy rule and the impact of emissions rebound on carbon dioxide and criteria air pollutant emissions, Environ. Res. Lett., 14(4), 044018,

Author Information

Sarah Benish ([email protected]), University of Maryland, College Park; and Melissa Fiffer, Harvard School of Public Health, Boston, Mass.

Citation: Benish, S., and M. Fiffer (2020), Affordable Clean Energy rule threatens progress of Clean Air Act, Eos, 101, Published on 18 November 2020.
Text © 2020. The authors. CC BY-NC-ND 3.0
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