Understanding the EPA’s National Emissions Inventory (NEI)

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The National Emissions Inventory is one of the many ways the Environmental Protection Agency (EPA) helps improve the nation’s air quality. This report helps the agency formulate action plans when an air quality problem raises its ugly head.

This article will cover the pollutants the report tracks, the negative impact of air pollution on health, and what you need to know about emissions inventories.

Criteria pollutants

The most common air pollutants in the US are something the EPA calls “criteria pollutants.” These are the atmospheric contaminants that cause the worst health effects and property damage and have a massive negative environmental impact.

Here are the current ones:

  • Carbon Monoxide (CO)
  • Lead (Pb)
  • Nitrogen Dioxide (NO2)
  • Ozone (O3)
  • Particulate matter (PM)
  •  Sulfur Dioxide (SO2)

Air pollution and its adverse effects

Air pollution is an ever-present environmental health hazard. When the government established the National Ambient Air Quality Standards in 1970, most experts considered air pollution to only harm respiratory health. However, over the decades, researchers have found that it also contributes to the following conditions:

  •  Cardiovascular disease
  •  Diabetes mellitus
  • Obesity
  • Reproductive, neurological, and immune system disorders

A study of over 57,000 women found that living near high-traffic highways could significantly increase a female’s chances of contracting breast cancer. Another study found that airborne toxic substances like methylene chloride are associated with an increased risk of this disease. Exposure to benzene (an industrial chemical and component of gasoline) has been shown to cause leukemia and is associated with non-Hodgkin’s Lymphoma.

Furthermore, exposure to air pollution causes inflammation and oxidative stress, which is associated with cancer and other chronic diseases. In 2020, the combination of massive air contamination from raging wildfires across the western part of the country and the COVID-19 pandemic proved to be a significant respiratory health challenge.

Traffic-related air pollution (TRAP)

This form of airborne contamination consists of carbon, ozone, nitrogen oxides, sulfur oxides, polycyclic aromatic hydrocarbons, and other compounds. Some older Americans exposed to TRAP suffer from reduced levels of high-density lipoprotein, otherwise known as good cholesterol. This increases their risk of heart disease.

TRAP also raises the risk of pregnant women contracting hypertensive disorders, which are dangerous changes in blood pressure. This is a leading cause of preterm birth, maternal and fetal illness and death, and low birth weight.


Ozone, an atmospheric gas, is called smog when it’s at ground level. Pollutants emitted by cars, power plants, industrial boilers, refineries, and other sources create ozone when they chemically interact with sunlight.

Ozone reacts with molecules in our airway lining, which causes acute inflammation. This may lead to shortness of breath, dry cough, pain when taking a deep breath, and wheezing. Prolonged ozone exposure can cause our airway lining to lose its ability to serve as a protective barrier to microbes and harmful chemicals.

Ozone triggers asthma and might worsen other respiratory conditions (such as pneumonia and bronchitis). High ozone concentrations make the muscles that control breathing more sensitive to dust and dry air.

Particulate matter

Chemicals such as nitrates, carbon, and mineral dust are all part of particulate matter. Concentrations are highest next to the source of emissions, such as power plants and highways.

Particulate matter doesn’t respect geographical boundaries and can freely move from one country to another. Because it’s more than 30 times thinner than human hair, it ends up in lung tissue, where it triggers severe breathing problems, impairs blood vessel function, and accelerates artery calcification.

However, particulate matter doesn’t only impact negatively on human health—it also significantly contributes to climate change because of its role in cloud formation.

Volatile organic compounds (VOCs)

These atmospheric contaminants are made up of carbon and hydrogen and vaporize at or near room temperature (hence the name). Paints, pesticides, cleaning supplies, gasoline, and other chemicals give off these toxic compounds.

VOCs typically give off a potent smell when they evaporate, making it easy to detect them. Besides giving off a disagreeable odor, VOCs can have a long-term adverse impact on your health. These effects include:

  • Eye, nose, and throat irritation
  • Chronic headaches
  • Chronic nausea
  • Loss of coordination
  • Liver, kidney, and central nervous system damage
  • Cancer

How does the EPA establish air quality standards?

The EPA is a federal agency with a mission to protect the environment so that everyone can breathe pristine air. By doing so, it protects the American public from significant health risks.

It administers all kinds of programs to accomplish this objective, including those that promote energy efficiency, sustainable growth, and pollution reduction. President Richard Milhous Nixon established the Environmental Protection Agency (EPA) in December 1970 through an executive order.

The Office of Air Quality Planning and Standards is the part of the EPA tasked with improving the quality of the country’s air. OAQPS manages programs to boost air quality in places where current conditions are significantly below acceptable standards. They also monitor air quality in areas where it’s relatively good to prevent it from deteriorating.

To do all that, they evaluate the current environmental status against established clean air standards and historical data. One of these standards is the National Ambient Air Quality Standard (NAAQS) for critical pollutants.

There are two types of standards—primary and secondary. Primary standards are those created to protect people from pollution-related health problems, such as cardiovascular disease. Secondary standards are in place to safeguard buildings, crops, and other nonhuman things from getting damaged.

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Air quality trends reports

To ensure air quality, the EPA publishes something it calls the National Air Quality and Emissions Trends Report, which looks at the air pollution trends of each of the six principal pollutants every year. Also included in the report is a summary of current air pollution levels.

What’s an emissions inventory?

An emissions inventory lists all the pollutants discharged into the atmosphere in a specified geographic region and predetermined period. The inventory includes air pollutants, such as sulfur dioxide (SO2), nitrogen oxides (NOx), and ammonia (NH3). It also includes greenhouse gasses like carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O).

The inventory lists the activities that cause emissions and the methodology used to collect the data. Researchers estimate emissions for each pollutant in the inventory by quantifying the intensity of each relevant activity in the geographical area within a specific period, otherwise known as the “activity rate.” This number is multiplied by a pollutant-dependent proportionality constant, which scientists call the “emission factor.”

All sources of pollutants must be identified to compile an emissions inventory. Clear distinctions must be made between sources related to the combustion of fossil fuels and those not caused by combustion.

Why are emissions inventories so crucial?

Emission inventory reports are crucial because environmental emissions are the source of many ecological problems. By looking at the data, scientists can understand pollution-related issues and develop action plans for solving them.

Policymakers rely on this information to track progress towards emission reduction targets. Scientists use this data to develop air quality models, mathematical simulations of how air pollutants disperse and react in the atmosphere and affect air quality. Individual facilities publish emission reports when they’ve violated EPA rules and need to ensure they’re in compliance.

Sometimes, annual reporting of the total amount of pollutants emitted by a particular country is necessary to monitor progress towards meeting agreed-upon emission reduction targets under international protocols and conventions. An example of this would be the annual emission inventories reported to the United Nations Framework Convention on Climate Change (UNFCCC) for greenhouse gasses and the UNECE Convention on Long-Range Transboundary Air Pollution (LRTAP) for air pollutants. 

What’s the EPA’s national emissions inventory (NEI)?

 In the US, the EPA compiles an annual National Emissions Inventory. This comprehensive and detailed estimate of emissions that contribute to air pollution is published every three years based on data provided by local, state, and tribal agencies.

Like all other emissions inventories, the purpose of the NEI is to help restore and preserve air quality, something that’ll also have a positive effect on climate change. States need this data to evaluate emissions trends and to compare these trends among states. The NEI is used in EPA modeling and regulatory analyses. It’s also used to produce the National Air Pollutant Emission Trends report.

The report contains emissions estimates for stationary locations. These include large industrial facilities, electric power plants, airports, and smaller industrial, non-industrial, and commercial facilities. Some states also voluntarily provide data on facilities such as gas stations, dry cleaners, and livestock operations.

Because of how stakeholders use the data, the NEI must be accurate and timely.

Positively impact the planet with Aspiration

For over 50 years, the EPA has been safeguarding the nation’s air quality, positively impacting the environment in the process. Their National Emissions Inventory is a big part of that success.

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