Air Pollution: Epa's List Of Identified Toxins

The United States Environmental Protection Agency (EPA) has identified six criteria air pollutants: carbon monoxide, lead, ground-level ozone, particulate matter, nitrogen dioxide, and sulfur dioxide. These pollutants are harmful to human health and the environment, and they can also cause property damage. The EPA has been monitoring air quality and working to reduce emissions of these pollutants, and air quality has improved nationally since 1980. Despite this progress, in 2023, about 66 million tons of pollution were emitted into the US atmosphere, and approximately 140 million people lived in counties with pollution levels above the primary National Ambient Air Quality Standards (NAAQS).

The six criteria air pollutants

The United States Environmental Protection Agency (EPA) has identified six common air pollutants, known as criteria air pollutants, which are found all over the country. These pollutants can harm human health, the environment, and cause property damage. The Clean Air Act requires the EPA to set National Ambient Air Quality Standards (NAAQS) for these six pollutants, in collaboration with state, tribal, and local air agencies.

Particle Pollution

Particle pollution, also known as particulate matter (PM), refers to a mixture of solid particles and liquid droplets in the air. These particles can include dust, dirt, smoke, soot, and aerosols. Particle pollution is a major concern as it can be inhaled and accumulate in the respiratory system, leading to respiratory and cardiovascular health issues.

Ground-level Ozone

Ground-level ozone is a harmful pollutant formed by the reaction of volatile organic compounds (VOCs) and nitrogen oxides (NOx) in the presence of sunlight. It is a key component of smog and can irritate the respiratory system, causing coughing, throat irritation, and chest tightness. Ground-level ozone is particularly harmful to children, the elderly, and individuals with pre-existing respiratory conditions.

Carbon Monoxide

Carbon monoxide (CO) is a colorless, odorless, and toxic gas produced by the incomplete combustion of fossil fuels. It poses a significant health risk as it binds to haemoglobin in the blood, reducing oxygen delivery to the body's tissues and organs. Exposure to carbon monoxide can lead to headaches, dizziness, nausea, and even death in extreme cases.

Sulfur Dioxide

Sulfur dioxide (SO2) is released into the atmosphere primarily during the burning of fossil fuels containing sulfur, such as coal and oil. It can also be emitted from industrial processes, such as smelting and paper milling. Sulfur dioxide contributes to acid rain, which damages ecosystems and infrastructure. Additionally, it irritates the eyes, nose, and throat, exacerbating respiratory conditions.

Nitrogen Dioxide

Nitrogen dioxide (NO2) is a highly reactive gas formed during the combustion of fossil fuels, particularly in high-temperature processes like vehicle engines and power generation. It is a major contributor to the formation of ground-level ozone and fine particulate matter. Nitrogen dioxide exposure is linked to respiratory problems, including asthma and bronchitis, and can reduce lung function.

Lead

Lead (Pb) is a toxic heavy metal that, when released into the atmosphere, can have detrimental effects on human health and the environment. Lead in the air primarily comes from industrial activities, such as metal smelting and waste incineration. Exposure to lead can cause neurological damage, especially in children, and is associated with behavioural problems, learning difficulties, and impaired cognitive development.

To address these criteria air pollutants, the EPA develops human health-based and environmentally based criteria, setting permissible levels to protect the public and the environment. These standards aim to mitigate the harmful impacts of air pollution and improve overall air quality across the United States.

Air pollution sources

Air pollution is generally categorised into four types of sources: mobile, stationary, area, and natural. Mobile sources include vehicles such as cars, buses, planes, trucks, and trains. These mobile sources account for more than half of the air pollution in the United States, with automobiles being the primary contributor. Stationary sources, on the other hand, refer to fixed locations like power plants, oil refineries, industrial facilities, and factories. While these sources emit large amounts of pollution, they are often concentrated in a single area.

Area sources encompass a range of smaller pollution sources that collectively have a significant impact. This includes agricultural areas, cities, and residential areas where activities such as heating, cooking, and the use of gas-powered equipment contribute to air pollution. Natural sources, such as wind-blown dust, wildfires, and volcanic eruptions, can also impact air quality, although they typically do not create ongoing pollution issues like the other sources.

Within these categories, there are various specific sources of air pollution. Vehicles, for instance, are a significant contributor, with tailpipe emissions from cars, trucks, and other diesel engines releasing harmful pollutants into the atmosphere. Industrial processes and power generation are another major source, including oil and gas development, iron and steel manufacturing, and the combustion of fossil fuels, which release a range of noxious gases and particulate matter. Residential and commercial activities also play a role, with heating and cooling equipment, wood fires, and gas-powered equipment contributing to local air pollution.

Additionally, certain compounds and chemicals further exacerbate air pollution. Volatile organic compounds (VOCs), for example, are found in paints, cleaning supplies, and even craft materials, and can vaporize at room temperature. Polycyclic aromatic hydrocarbons (PAHs), another type of organic compound, are widespread in the environment due to combustion and industrial processes, and are also found in particulate matter. The Clean Air Act, implemented by the EPA, aims to address these issues by setting National Ambient Air Quality Standards (NAAQS) for six commonly found air pollutants, known as criteria air pollutants.

Air quality trends

The U.S. Environmental Protection Agency (EPA) has been working to protect public health and improve air quality by reducing pollutant emissions for over 50 years. The Clean Air Act, in place for half a century, has resulted in cleaner air and reduced health risks for Americans.

The EPA produces annual reports on the nation's air quality status and trends. These reports include data on air quality concentrations, which can vary from year to year due to pollution emissions, natural events such as dust storms and wildfires, and weather variations. The EPA also provides Air Quality Trends summaries, which reflect actual air quality and include concentrations impacted by episodic events.

The EPA's work is focused on six commonly found air pollutants, known as criteria air pollutants. These include sulfur dioxide (SO2), oxides of nitrogen (NOx), ozone (O3), carbon monoxide (CO), volatile organic compounds (VOCs), and certain toxic air pollutants. From 1990 to 2017, emissions of air toxics declined by 74%, thanks to federal and state regulations and technological advancements. Overall, national air quality concentration averages for these criteria air pollutants have been on a decline from 1990 to 2021.

In addition to the criteria air pollutants, particle pollution (PM2.5 and PM10) is another area of concern. This type of pollution includes compounds such as sulfates, nitrates, elemental (black) carbon, organic carbon, and crustal material. The EPA's Air Quality Design Values exclude concentrations impacted by exceptional events, which are defined as unusual or naturally occurring events that affect air quality but are beyond the control of state or local agencies. By classifying non-attainment areas based on these values, the EPA can work towards attaining National Ambient Air Quality Standards (NAAQS) throughout the country.

Air toxics

Hazardous air pollutants, also known as air toxics, are substances that are known or suspected to cause cancer, birth defects, and other serious health issues. These pollutants come from a variety of sources, including emissions from coal-fired power plants, industries, refineries, vehicles, and certain industrial processes. The Clean Air Act mandates the EPA to regulate these hazardous air pollutants from specific categories of industrial facilities in two phases.

The EPA has classified 188 pollutants as hazardous, with 33 of them rated as the greatest threat to public health in urban areas. These air toxics are monitored through the National Air Toxics Assessment, which provides maps and lists of these pollutants by state or county. Additionally, the Toxics Release Inventory allows individuals to learn about releases of toxic chemicals into the environment through air, water, and land from manufacturing facilities.

The EPA has introduced the Air Toxics Screening Assessment (AirToxScreen), a new tool that provides communities with updated data and risk analyses on air toxics annually. This tool assists state, local, and tribal air agencies, the EPA, and the public in identifying existing and emerging air toxics issues. It is part of the EPA's proactive approach to addressing air toxics and improving air quality.

Major sources of outdoor air toxics include emissions from coal-fired power plants, industries, and refineries. Certain industries, such as medical equipment sterilization facilities, may release ethylene oxide, contributing to air toxicity. Indoor air can also contain hazardous pollutants from tobacco smoke, building materials like asbestos, and consumer products such as cleaning supplies and air fresheners.

Reducing emissions of urban air toxics has been a priority for the EPA since the Clean Air Act Amendments in 1990. The EPA utilizes hazardous air pollutant emissions and ambient monitoring data to develop regulatory programs aimed at limiting emissions from stationary sources. These efforts contribute to the overall goal of improving air quality and protecting public health.

Air quality standards

The United States Environmental Protection Agency (EPA) has established the National Ambient Air Quality Standards (NAAQS) for six principal pollutants, also known as "criteria pollutants". These pollutants are common in outdoor air and are harmful to public health and the environment. The Clean Air Act, last amended in 1990, requires the EPA to set these standards and review them periodically, along with the science behind them, to determine if changes are needed.

The six criteria pollutants are:

• SO2
• NO2
• O3
• Pb
• Particle pollution
• One other pollutant that is yet to be identified

The NAAQS are designed to protect public health and welfare. Primary standards aim to protect public health, including sensitive populations such as asthmatics, children, and the elderly, by ensuring an adequate margin of safety. Secondary standards aim to protect public welfare, including soils, water, crops, vegetation, animals, wildlife, weather, visibility, and climate. They also aim to prevent damage to property, transportation hazards, and adverse effects on economic values, personal comfort, and well-being.

The EPA also establishes an Air Quality Index (AQI) for five major air pollutants regulated by the Clean Air Act. The AQI is a scale from 0 to 500, with higher values indicating greater levels of air pollution and health concerns. An AQI value of 50 or below represents good air quality, while a value over 300 indicates hazardous air quality.

Air quality trends summaries reflect actual air quality and include concentrations impacted by events like wildfires and dust storms. Air Quality Design Values are used to classify non-attainment areas, indicating air quality unaffected by exceptional events. Exceptional events are defined as unusual or naturally occurring events that affect air quality but cannot be reasonably controlled by tribal, state, or local air agencies.

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