Clearing the Air

Power plants and industrial facilities fueled by natural gas contribute hugely to several types of air pollution that damage our environment, exacerbate climate change, and pose a serious risk to people's health. But major pollutants from gas-fired combustion turbines — namely, nitrogen oxides (NOx), greenhouse gases (GHGs), and hazardous air pollutants – are not yet subject to comprehensive, protective federal clean air safeguards. Recently, the Environmental Protection Agency (EPA) unveiled a proposal to strengthen pollution limits for NOx. By law, the public has the opportunity to comment on the proposal and EPA must consider these comments when shaping the final standards. This process provides the public with the opportunity to shape these protections to ensure healthy, clean air for all.

The Clean Air Act requires the EPA to set air quality standards that limit the amount of pollution that can be in the air and limit the level of emissions coming from specific sources, including gas-fired combustion turbines – the engines that burn fuel to produce electricity or mechanical power at power plants and industrial facilities, and release pollution into the air as a result. EPA has an obligation to limit this pollution at the federal level and states can impose even stronger standards at the state-level.

Currently, there is a need to strengthen each major category of pollution emitted by gas-fired turbines:

Strengthened NOx Standards: Strengthened standards are needed to protect the public from NOx pollution emitted by the power sector and industrial sector. EPA has not updated the NOx standards for gas-fired turbines since 2006. Today, gas-fired turbines can produce power at emissions rates 87 percent lower than EPA's 2006 standard through use of common pollution controls.

New Greenhouse Gas Standards: Comprehensive GHG standards are needed to protect people from greenhouse gas pollution emitted by existing gas-fired combustion turbines in the power sector. While EPA has set GHG standards for new gas-fired combustion turbines, there are currently no GHG standards for such existing plants.

Strengthened Hazardous Air Pollutant Standards: Strengthened standards are needed to protect people from toxic air pollution emitted by gas-fired stationary combustion turbines in the power and industrial sector. EPA has not updated these standards since 2004. Currently, the standards do not require that turbines install any controls, leaving threats to public health wide open. Moreover, emissions estimates for hazardous air pollutants are likely only a fraction of actual pollution from facilities. We need more and better data about these pollutants, and we need standards to reduce them and keep us all safe

So, what exactly is a gas-fired combustion turbine?

A gas-fired combustion turbine is a type of engine that burns gas to create mechanical power. There are two common types of combustion turbine configurations: combined-cycle units and simple-cycle units. Combined-cycle units combine a stationary combustion turbine with a heat-recovery steam generator that captures and uses exhaust waste heat from the first cycle to generate additional power. These are typically larger, more fuel-efficient units that run more often.

Simple-cycle units are typically smaller, less fuel-efficient units that run less often. This fuel-inefficiency means simple-cycle units produce more pollution per unit of electricity generated than combined-cycle units.

Both types of combustion turbines are used in the power sector, to create electricity, as well in the industrial sector to drive operations used in glass manufacturing, plastics production, steel mill operations, chemical manufacturing and more.

Check out our glossary of terms for more information on the technical aspects of combustion turbine operations.

Nitrogen Oxides Harms

Exposure to NOx emissions from combustion turbines can contribute to a range of serious health problems – such as heart disease, permanent lung damage, strokes, or aggravation of asthma – and premature deaths.

One of the primary pollutants resulting from natural gas combustion is a class of pollutants known as NOx. Exposure to NOx can cause numerous health issues. NOx is a particularly dangerous pollutant because it is a precursor for both smog (ozone) and soot (particulate matter) pollution. Ground-level ozone and particulate matter are linked to cardiovascular illnesses, respiratory problems, and premature death, both in the short term and over a longer duration.

Exposure to ozone and particulate matter is particularly harmful for vulnerable groups, like children (four million of whom have asthma in the US), people with respiratory diseases or asthma, older adults, and outdoor workers. Study of air pollution and the Medicare population shows a significant association between ozone exposure and mortality, with effects strongest in communities of color and lower socioeconomic communities.

EPA's recent proposal presents the opportunity to revise federal NOx pollution standards and ensure that the standards sufficiently protect the environment and people's health. Notably, EPA has not updated the NOx standards since 2006. Today, gas-fired power plants are achieving rates that are 87 percent lower than EPA's 2006 standard through use of a widely available control technology known as selective-catalytic reduction or "SCR."

Greenhouse gas harms

Fossil fuel-fired power plants, including those using gas turbines, are responsible for about one-quarter of our nation's total greenhouse gas pollution.

Power plants are responsible for 1.4 billion tons of emissions a year, one of the largest sources in the world. Greenhouse gases are a group of pollutants, including carbon dioxide, that trap heat in the atmosphere and contribute to climate change. Emissions of carbon dioxide from gas-fired power plants in the United States have almost doubled between 2005 and 2021.

Greenhouse gas pollution threatens public health and safety and the environment. As the climate changes due to greenhouse gas pollution, more people are exposed to dangerous and potentially deadly extreme weather events and climate disasters have been increasing in frequency and intensity: since 1980, there have been 376 weather and climate disasters in the U.S. costing more than $1 billion, with more than one-quarter of these events occurring in the past five years, according to NOAA.

Although the EPA issued greenhouse gas standards for new gas power plants, existing gas power plants are not subject to any current greenhouse gas standards - but the Clean Air Act requires that EPA promulgate technology-based emissions standards for harmful climate pollution from existing gas-fired power plants. These standards would allow power companies to achieve required pollution reductions through an array of available low and zero-emitting solutions. Clean, renewable energy options are emission-free, more affordable than ever, reliable, and the leading source of new electricity generation being deployed.

In addition to federal standards, states can mandate strong pollution limits and clean energy solutions. For example, eleven Northeastern states are part of the Regional Greenhouse Gas Initiative, where each state has established individual carbon pollution budgets as part of a regional cap and trade program. In addition, 24 states and the District of Columbia have enacted 100% clean energy goals.

Hazardous air pollutant harms

Gas turbines emit other highly toxic pollutants that can cause cancer and developmental harms.

Gas turbines also emit hazardous air pollutants, which are a particularly harmful class of pollutants linked to cancer, reproductive harms, developmental harms, among other negative impacts.

Hazardous air pollutants emitted by gas turbines include formaldehyde, polycyclic aromatic hydrocarbons (PAH), benzene, toluene, xylenes, and others. EPA's toxicology review of one of those pollutants, formaldehyde, notes that inhaling it can cause cancer in humans (PDF) and that exposure can lead to effects ranging from wheezing and bronchitis to reproductive and developmental toxicity and worse. The agency's National Air Toxics Assessment notes that about half of the nationwide average cancer risk (PDF) from breathing air toxics comes from formaldehyde.

EPA has not updated the Hazardous Air Pollution standards since 2004. Currently, the standards do not require that turbines install protective controls. In addition, the emissions factors – values used to represent emissions based on associated activity – used to calculate hazardous air pollution allow for industry and EPA to underestimate emissions. EPA can update emissions factors to ensure emissions are more accurately calculated. EPA can also issue protective standards based on use of oxidation catalyst and dual-oxidation catalyst – controls that limit hazardous air pollution – and continuous emissions monitoring, or CEMS, to monitor emissions and ensure proper operation of controls.

States can also provide important protections by imposing more stringent standards at the state-level. For example, Massachusetts has more stringent standards for certain hazardous pollutants. In addition, Louisiana regulates additional pollutants that are not subject to federal standards.

Communities near power plants are more likely to have higher populations of people of color, and higher poverty rates

The public health and environmental burden of air pollution often falls disproportionately on people of color and those with lower-incomes. Numerous studies show correlations between power plant locations or emissions and lower-income communities of color. The EPA identifies environmental justice (EJ) populations as the highest intersection of low-income populations, people of color, and a given environmental indicator, such as ozone level in the air. A larger share of EJ populations live near electric power plants, according to an analysis of Regional Greenhouse Gases Initiative data. Specifically, 42.6% of EJ communities in this study had between two and five power plants in their community, whereas only 28% of non-EJ communities had the same amount.

Differences in people's health depending on their racial or ethnic group or socioeconomic status can be linked to environmental factors and increased exposure to environmental hazards. For this reason, areas with particularly high levels of pollution are sometimes called "sacrifice zones," referring to the low-income and racial and ethnic minority populations whose health gets sacrificed.

Some areas with already-dense concentrations of turbines could be at risk of worsening pollution in the coming years. Researchers expect an increase in gas-fired power plant construction to support data centers due to the rise in electricity demand spurred by artificial intelligence. Where these facilities are built is largely determined by state regulatory conditions, and researchers expect that Texas, Oklahoma, and Louisiana are likely host states for additional gas-fired power plants. Analysts forecast that Texas, in particular, could see nearly a quarter of all load growth in the U.S. over the next decade because of its regulatory environment, land availability, and natural gas resources.

Figure 1 below illustrates where existing turbines are located and show clusters in regions with historically overburdened communities, including in the Houston-Galveston region in Texas, Long Beach-Bakersfield region in California, New York City, and southern Louisiana.

Which U.S. states and Congressional districts have the highest emissions?

Certain regions across the US have particularly high emissions of carbon dioxide, nitrogen oxide, and formaldehyde.

Where are the highest levels of carbon dioxide pollution?

Texas (91,547,909 short tons), Florida (77,892,798 short tons), and Pennsylvania (51,154,770 short tons) had the highest carbon dioxide emissions nationwide, according to 2022 data.

On the Congressional district level, Florida's 18th district in south-central Florida recorded the highest carbon dioxide emissions in the country at 17,931,996 short tons in 2022. Ohio's sixth Congressional district on the state's eastern border, followed at 11,016,472 short tons. And Florida's 20th Congressional district in the southeastern part of the state had the third-highest measure of carbon dioxide emissions in the country at 10,633,288 short tons.

Where are the highest levels of NOx pollution?

Texas (18,913 short tons), Florida (12,269 short tons), and Michigan (5,877 short tons) had the highest NOx pollution, according to 2022 data.

The highest nitrogen oxide emissions in a Congressional district were seen in Michigan's eighth district, which includes the city of Flint, at 3,021 short tons in 2022. Florida's 18th district followed with 2,530 short tons, and Florida's 12th district, on the state's west coast, had the third-highest NOx emissions in the country at 2,247 short tons.

Where is the highest potential for uncontrolled formaldehyde pollution?

Texas (2,031 short tons), Florida (1,633 short tons), and California (888 short tons) had the highest potential for uncontrolled formaldehyde pollution in 2022.

The top three Congressional districts with the highest uncontrolled formaldehyde emissions in 2022 were Florida's 18th district with 286 short tons, Texas's 36th district with 256, and Arizona's ninth district with 254 short tons.

Uncontrolled measures refer to situations where emission sources have no controls and represent the worst case scenario of emissions. These emissions are estimations calculated through use of emissions factors, which can also allow for underestimates of emissions.

Take Action

Despite the damaging impact of these pollutants, we can take action to limit these emissions. EPA's recent proposal for strengthened NOx standards presents a unique opportunity for the public to help shape these protections. Pollution from gas-fired power plants harms millions across the country – take action now by commenting on EPA's proposal and letting EPA know we need protective standards.