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There are many types of air pollutants regulated under the Clean Air Act, including six “criteria" or generally pervasive pollutants – carbon monoxide, nitrogen oxides, particulate matter, sulfur dioxide, lead and ozone - as well as 187 hazardous air pollutants specifically listed in the statute. These pollutants are responsible for a wide range of adverse health and environmental effects.

Ozone / Smog

Summary: 

Ozone – the chemical compound O3 – is found both at ground level (i.e., ambient ozone) and in the upper portions of the Earth’s atmosphere (i.e., stratospheric ozone). Ozone in the ambient air - commonly referred to as smog – is not emitted directly by any source. Instead it is formed through a reaction of precursor pollutants in the presence of sunlight.

Ozone – the chemical compound O3 – is found both at ground level (i.e., ambient ozone) and in the upper portions of the Earth’s atmosphere (i.e., stratospheric ozone). In the upper atmosphere, ozone provides a protective layer from the harmful rays of the sun. However, in the ambient air, ozone is what is commonly referred to as smog.

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Particle Pollution

Summary: 

Particle pollution – known as particulate matter (PM) – is a mixture of solid particles and liquid droplets found in the air. Some particles, like soot, are large or dark enough to be visible to the naked eye, while others are so tiny they can only be seen with an electron microscope.

Particle pollution – known as particulate matter (PM) – is a mixture of solid particles and liquid droplets found in the air. Some particles, like soot, are large or dark enough to be visible to the naked eye, while others are so tiny they can only be seen with an electron microscope. Particle pollution includes inhalable coarse particles, referred to as PM10 because they have a diameter greater than 2.5 micrometers and less than 10 micrometers, and fine particles, referred to as PM2.5 because they have a diameter less than 2.5 micrometers.

Nitrogen Oxides

Summary: 

Nitrogen oxides (NOx) consist of a variety of reactive gases composed of different levels of nitrogen and oxygen and are most typically formed from the combustion of certain fuels (oil, coal, gasoline, diesel) at high temperatures.

Nitrogen oxides (NOx) consist of a variety of reactive gases composed of different levels of nitrogen and oxygen and are most typically formed from the combustion of certain fuels (oil, coal, gasoline, diesel) at high temperatures.  Industrial processes, power plants and mobile sources (including passenger cars, trucks, buses, ships, aircraft, locomotives and construction and farm equipment) are among the most significant sources of NOx in the U.S.  As a contributor to ozone (smog), particle pollution, haze, toxic air pollution, global warming, acid rain and

Sulfur Dioxide

Summary: 

Sulfur dioxide (SO2 ) is one of a collection of highly reactive gases known as oxides of sulfur (SOx). Over 90 percent of SO2  emissions come from fossil fuel combustion at power plants and other industrial facilities.

Sulfur dioxide (SO2) is one of a collection of highly reactive gases known as oxides of sulfur (SOX). Over 90 percent of SO2 emissions come from fossil fuel combustion at power plants and other industrial facilities. Smaller sources of SO2 include industrial processes like extracting metal from ore and, to a lesser extent, the burning of high-sulfur fuel by locomotives, marine engines and nonroad engines and equipment, as well as onroad mobile sources, fires, waste disposal, residential wood combustion and solvent use.

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Haze

Summary: 

Regional haze is the result of a number of sources and activities located across a broad geographic area emitting fine particle pollution, known as PM2.5, and its precursors, including sulfur dioxide and oxides of nitrogen. Sources of fine particles and their precursors can be natural or manmade.

Regional haze is the result of a number of sources and activities located across a broad geographic area emitting fine particle pollution, known as PM2.5, and its precursors, including sulfur dioxide (SO2) and oxides of nitrogen (NOx). Sources of fine particles and their precursors can be natural, such as windblown dust and wildfires, as well as manmade, such as power plants, other industrial operations, motor vehicles and forest and agricultural burning.

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Toxic Air Pollutants

Summary: 

Toxic air pollutants, also referred to as hazardous air pollutants, are substances that cause or may cause cancer or other serious health effects, such as reproductive, birth or developmental defects, and neurological, cardiovascular, and respiratory disease. They can be found in gaseous, aerosol, or particulate forms.

Toxic air pollutants, also referred to as hazardous air pollutants, are substances that cause or may cause cancer or other serious health effects, such as reproductive, birth or developmental defects, and neurological, cardiovascular, and respiratory disease. They can be found in gaseous, aerosol, or particulate forms. Some toxic air pollutants (e.g., mercury) are persistent bioaccumulative toxics, which means they are stored indefinitely in the body and increase over time.

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Climate Change is the warming of the earth's atmosphere due to increased concentrations of greenhouse gases emitted from human and other activities.  Human activities have substantially increased the amount of greenhouse gases (e.g., carbon dioxide and methane) in the atmosphere, causing the atmosphere to trap more heat and leading to changes in the Earth’s climate.

Federal

Summary: 

During the 2009 international climate change negotiations in Copenhagen, Denmark, President Barack Obama announced a goal of reducing U.S. greenhouse gas emissions by 17 percent below 2005 levels by 2020. Since that time, the President has proposed and begun implementing a series of measures in order to achieve this reduction target. More recently, on June 25, 2013, the President issued his Climate Action Plan, a multi-pronged approach to address global warming emissions from new and existing power plants.

On June 25, 2013, President Obama announced his Climate Action Plan, a multi-pronged approach to address global warming by reducing U.S. greenhouse gas emissions, adapting to the effects of global warming and participating in international efforts to address global warming. The Climate Action plan includes a commitment to reduce U.S. greenhouse gas emissions to 17 percent below 2005 levels by 2020.

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State/Local

Summary: 

Multi-state oranizations and state and local governmental agencies are implementing their own global warming initiatives to reduce greenhouse gas emissions. For example, the Regional Greenhouse Gas Initiative (RGGI or "ReGGIe") is a cooperative effort among the states of Connecticut, Delaware, Maine, Maryland, Massachusetts, New Hampshire, New York, Rhode Island and Vermont under which the states have capped and will reduce carbon dioxide emissions from the power sector 10 percent by 2018. Thirty four states and D.C. have completed Climate Action Plans.

Multi-state organizations and state and local governmental agencies are implementing their own global warming initiatives to reduce greenhouse gas emissions. For example, the Regional Greenhouse Gas Initiative (RGGI or "ReGGIe") is a cooperative effort among the states of Connecticut, Delaware, Maine, Maryland, Massachusetts, New Hampshire, New York, Rhode Island and Vermont under which the states have capped and will reduce carbon dioxide emissions from the power sector 10 percent by 2018.

International

Summary: 

In 1992, 188 countries negotiated the U.N. Framework Convention on Climate Change (UNFCCC). The UNFCCC went into effect in 1993 after it was ratified by 50 nations, including the United States. The UNFCCC contains voluntary commitments by industrialized nations to reduce their greenhouse gas emissions to 1990 levels by 2000, a target that was not met.

In 1992, 188 countries negotiated the U.N. Framework Convention on Climate Change (UNFCCC). The UNFCCC went into effect in 1993 after it was ratified by 50 nations, including the United States. The UNFCCC contains voluntary commitments by industrialized nations to reduce their greenhouse gas emissions to 1990 levels by 2000, a target that was not met. The ultimate objective of the UNFCCC is to achieve stabilization of GHG concentrations in the atmosphere at a level that would prevent dangerous man-made disruption of the global climate system.

Science

Summary: 

Research on the causes and impacts of global warming is conducted by organizations at all levels of society: academic institutions, nongovernmental groups, the U.S. and other governments, and international institutions. The Intergovernmental Panel on Climate Change (IPCC) is the leading international body for the assessment of climate change.

Research on the causes and impacts of global warming is conducted by organizations at all levels of society: academic institutions, nongovernmental groups, the U.S. and other governments, and international institutions. The Intergovernmental Panel on Climate Change (IPCC) is the leading international body for the assessment of climate change.

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Enforcement is a critical component of regulatory air quality programs that helps ensure a level playing field across all companies in an industrial sector. Appropriate methods of enforcement ensure compliance with regulations which helps improve human health and the environment by ensuring that required reductions in air pollution actually occur.

Enforcement and Compliance

Summary: 

Air quality agencies carry out enforcement and compliance programs to ensure that sources meet the applicable federal, state and local air pollution control requirements in their jurisdictions. There are several aspects of an agency’s enforcement and compliance program. EPA and state and local air agencies often provide compliance assistance to help the regulated community understand and comply with regulations.

Air quality agencies carry out enforcement and compliance programs to ensure that sources meet the applicable federal, state and local air pollution control requirements in their jurisdictions. There are several aspects of an agency’s enforcement and compliance program.  EPA and state and local air agencies often provide compliance assistance to help the regulated community understand and comply with regulations.

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Training

Summary: 

State and local air quality officials receive training on air pollution from a number of training providers. EPA provides training to state and local air agencies via self-instructional courses, webinars and through classroom course materials (known as the Air Pollution Training Institute, APTI). Regional state organizations focusing on air quality issues develop and hold training courses, through classroom courses, workshops, conference and webinars.

State and local air quality officials receive training on air pollution from a number of training providers. EPA provides training to state and local air agencies via self-instructional courses, webinars and through classroom course materials (known as the Air Pollution Training Institute, APTI). Regional state organizations focusing on air quality issues develop and hold training courses, through classroom courses, workshops, conference and webinars. California’s Air Resources Board is a major training provider and has developed its own curriculum of courses.

Funding

Summary: 

State and local air pollution control programs in the United State are funded through a variety of sources. These include federal, state and local appropriations; the federal permit fee program under Title V of the Clean Air Act; state and local permit and emissions fee programs; and other funding programs that individual agencies operate.

State and local air pollution control programs in the United State are funded through a variety of sources. These include federal, state and local appropriations; the federal permit fee program under Title V of the Clean Air Act; state and local permit and emissions fee programs; and other funding programs that individual agencies operate. Federal grants are provided under two provisions of the Clean Air Act:  Sections 103 and 105.

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Industrial sources of air pollution, including power plants, manufacturing facilities and agricultural operations, emit a variety of pollutants that cause or contribute to substantial health and environmental problems throughout the country.

Power Plants

Summary: 

Power plants are currently the dominant emitters of mercury (50 percent), sulfur dioxide (60 percent), acid gases (over 75 percent) and arsenic (62 percent) in the United States. They are also a significant source of emissions of greenhouse gases (34 percent) and nitrogen oxides (13 percent). Most of these emissions come from coal- and oil-fired power plants.

Power plants are currently the dominant emitters of mercury, sulfur dioxide, acid gases and arsenic in the United States, and they are major sources of nitrogen dioxide emissions. In addition, about one third of the nation’s greenhouse gas emissions come from power plants.

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Manufacturing Facilities

Summary: 

Manufacturing facilities are among the industries in the United States that are responsible for emissions of air pollution. These include factories and other operations, large and small, that produce goods that will be used by individual consumers (e.g., automobiles, appliances, clothing, food). They also include facilities that make intermediate goods that are destined for other manufacturing plants, such as building materials and parts to be used in the creation of end-use items.

Manufacturing facilities are among the industries in the United States that are responsible for emissions of air pollution. These include factories and other operations, large and small, that produce goods that will be used by individual consumers (e.g., automobiles, appliances, clothing, food). They also include facilities that make intermediate goods that are destined for other manufacturing plants, such as building materials and parts to be used in the creation of end-use items.

Agriculture

Summary: 

Agriculture comprises many types of activities, from crop production to raising animals for food. Agricultural activities contribute directly to emissions of air pollutants through a variety of processes: enteric fermentation in domestic livestock (i.e., methane gas produced during digestion), manure management, rice cultivation, agricultural soil management, machines used in agricultural operation (e.g., diesel irrigation pumps) and burning of agricultural residues.

Agriculture comprises many types of activities, from crop production to raising animals for food. Agricultural activities contribute directly to emissions of air pollutants through a variety of processes: enteric fermentation in domestic livestock (i.e., methane gas produced during digestion), manure management, rice cultivation, agricultural soil management, machines used in agricultural operation (e.g., diesel irrigation pumps) and burning of agricultural residues.

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As state and local air pollution control agencies work to achieve their clean air goals, they must, among many other things, measure levels of pollution in the air, issue "permits" for facilities to operate, inspect sources to ensure they comply with clean air regulations, hire and train staff to carry out these activities and seek adequate funding to run clean air programs.

Measuring Air Pollution

Summary: 

An important aspect of air quality control is measuring air pollution. This involves two types of measurements. First, air quality control agencies measure the ambient air to determine whether or not an area is meeting EPA’s health-based air quality standards. Ambient air monitoring is conducted via a network of monitors throughout the country that measure actual concentrations of various air pollutants, including sulfur dioxide, nitrogen dioxide, ozone, lead, particulate matter, carbon monoxide, and several toxic air pollutants.

Air quality control agencies measure pollutants in the ambient air to determine whether an area is meeting EPA’s air quality standards. Ambient air monitoring is conducted via networks of monitors located throughout the country that measure actual concentrations of various air pollutants, including sulfur dioxide, nitrogen dioxide, ozone, lead, particulate matter, carbon monoxide, and several toxic air pollutants.

Enforcement and Compliance

Summary: 

Air quality agencies carry out enforcement and compliance programs to ensure that sources meet the applicable federal, state and local air pollution control requirements in their jurisdictions. There are several aspects of an agency’s enforcement and compliance program. EPA and state and local air agencies often provide compliance assistance to help the regulated community understand and comply with regulations.

Air quality agencies carry out enforcement and compliance programs to ensure that sources meet the applicable federal, state and local air pollution control requirements in their jurisdictions. There are several aspects of an agency’s enforcement and compliance program.  EPA and state and local air agencies often provide compliance assistance to help the regulated community understand and comply with regulations.

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Permitting

Summary: 

All major facilities, ranging from power plants to refineries, are required under the Clean Air Act to obtain a permit. There are two main types of air pollution permits: preconstruction permits and operating permits. Sources must apply for preconstruction permits before building a new facility, or beginning major modifications to an existing facility, if the facility is expected to increase its emissions of regulated air pollutants by significant amounts.

Air quality control agencies determine the pollution control technologies, emission limits and other requirements applicable to stationary sources, such as power plants, through the permitting process. All major facilities, ranging from power plants to refineries, are required under the Clean Air Act to obtain a permit. There are two main types of air pollution permits: preconstruction permits and operating permits.

Training

Summary: 

State and local air quality officials receive training on air pollution from a number of training providers. EPA provides training to state and local air agencies via self-instructional courses, webinars and through classroom course materials (known as the Air Pollution Training Institute, APTI). Regional state organizations focusing on air quality issues develop and hold training courses, through classroom courses, workshops, conference and webinars.

State and local air quality officials receive training on air pollution from a number of training providers. EPA provides training to state and local air agencies via self-instructional courses, webinars and through classroom course materials (known as the Air Pollution Training Institute, APTI). Regional state organizations focusing on air quality issues develop and hold training courses, through classroom courses, workshops, conference and webinars. California’s Air Resources Board is a major training provider and has developed its own curriculum of courses.

Funding

Summary: 

State and local air pollution control programs in the United State are funded through a variety of sources. These include federal, state and local appropriations; the federal permit fee program under Title V of the Clean Air Act; state and local permit and emissions fee programs; and other funding programs that individual agencies operate.

State and local air pollution control programs in the United State are funded through a variety of sources. These include federal, state and local appropriations; the federal permit fee program under Title V of the Clean Air Act; state and local permit and emissions fee programs; and other funding programs that individual agencies operate. Federal grants are provided under two provisions of the Clean Air Act:  Sections 103 and 105.

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State and Local Stringency

Summary: 

The Clean Air Act allows state and local air pollution control agencies to adopt programs more stringent than those of the federal government.  In reality, most state agencies are still not able to adopt more stringent programs, due to state or local law, regulation, policy or other restrictions.  NACAA conducted a survey of state and local air agencies in September and October 2014 and discovered that over one-half of state respondents are precluded from adopting measures more stringent than federal requirements, or may do so only under special circumstances. Read Restrictions on the Stringency of State and Local Air Quality Programs (December 8, 2014) for details on the survey results.

The Clean Air Act allows state and local air pollution control agencies to adopt programs more stringent than those of the federal government.  In reality, most state agencies are still not able to adopt more stringent programs, due to state or local law, regulation, policy or other restrictions.  NACAA conducted a survey of state and local air agencies in September and October 2014 and discovered that over one-half of state respondents are precluded from adopting measures more stringent than federal requirements, or may do so only under special circumstances.

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Passenger cars, trucks, buses, ships, locomotives, aircraft and other vehicles and engines, as well as the fuel that run them, represent a principal source of air pollution in the U.S. contributing to serious air quality and environmental problems, such as elevated levels of smog, soot, toxic air pollutants, climate change and acid rain.

Passenger Cars

Summary: 

The U.S. passenger car fleet consists of more than 200 million cars and light-duty trucks (referred to collectively as light-duty vehicles). Forty years ago almost all personal vehicles were cars. Today, at least half of all vehicle sales for personal use are sport utility vehicles (SUVs), vans and pickup trucks. Title II of the Clean Air Act required EPA to promulgate a series of rules to reduce passenger car tailpipe emissions, as well as emissions from refueling and the evaporation of gasoline in the tank.

The U.S. passenger car fleet consists of more than 200 million cars and light-duty trucks (referred to collectively as light-duty vehicles). When the Clean Air Act was enacted in 1970, almost all personal vehicles were cars. Today, at least half of all vehicle sales for personal use are sport utility vehicles (SUVs), vans and pickup trucks. Title II of the Clean Air Act required EPA to promulgate a series of rules to reduce passenger car tailpipe emissions, as well as emissions from refueling and the evaporation of gasoline in the tank.

Trucks and Buses

Summary: 

Diesel-fueled trucks and buses have served the nation’s freight and transportation needs for over half a century because of their reliability, durability and relative efficiency. This source category includes a wide variety of vehicles from 18-wheel tractor-trailer combinations, to school and transit buses to dump trucks and refuse haulers. These vehicles can be found in large numbers on major highway, urban streets and rural roads.

Diesel-fueled trucks and buses have served the nation’s freight and transportation needs for over half a century because of their reliability, durability and relative efficiency. This source category includes a wide variety of vehicles from 18-wheel tractor-trailer combinations, to school and transit buses to dump trucks and refuse haulers. These vehicles can be found in large numbers on major highways, urban streets and rural roads.

Fuels

Summary: 

Controlling the content and properties of transportation fuels can offer great benefits in terms of protecting public health and the environment, particularly when cleaner fuels are combined with vehicle and engine emission standards. In 1974, EPA put in place a program to gradually reduce lead in gasoline. Lead in gasoline has been banned entirely since 1996. More recently, federal programs have required "reformulation" of gasoline and significant reductions in sulfur levels of gasoline, allowing the pollution control equipment to work more efficiently.

Controlling the content and properties of transportation fuels can offer great benefits in terms of protecting public health and the environment, particularly when cleaner fuels are combined with vehicle and engine emission standards. In 1974, EPA put in place a program to gradually reduce lead in gasoline. Lead in gasoline has been banned entirely since 1996.

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Ships, Trains and Aviation

Summary: 

Large ships, locomotives and aircraft are all considered “nonroad” vehicles or engines. Ocean-going ships – such as diesel-fueled container ships, cruise ships, tankers and bulk carriers – travel around the world and contribute significantly to air pollution in many of our nation’s cities and ports, as well as inland areas. Likewise, locomotive engines, which power trains that transport vast quantities of goods and also serve as a mode of transportation, run on diesel fuel and play a role in air pollution levels across the country. Meanwhile, the rapid growth in worldwide air travel has heightened concerns over the influence of aviation on air quality while piston-engine aircraft, used for general aviation, are fueled with leaded aviation gasoline and are a significant source of lead emissions.
 

Large ships, locomotives and aircraft are all considered “nonroad” vehicles or engines. Ocean-going ships, often referred to as Category 3 (C3) marine engines, are the largest ships on the water and include container ships, cruise ships, tankers and bulk carriers. These large, diesel-fueled vessels travel around the world and contribute significantly to air pollution in many of our nation’s cities and ports, as well as inland areas.