Under the federal Clean Air Act, EPA has identified six major air pollutants that have adverse effects on public health and the environment called "criteria air pollutants": ozone, carbon monoxide, nitrogen dioxide, sulfur dioxide, particulate matter, and lead. EPA has set National Ambient Air Quality Standards for each of these criteria pollutants to protect public health and the environment. In addition to the criteria pollutants, other air pollutants of concern include toxic air pollutants, persistent bioaccumulative toxics, such as mercury and dioxin, and greenhouse gases.
This page provides general information about the criteria pollutants and toxic air pollutants. Clicking on the pollutant link will lead to further information, such as specific issues, rules, fact sheets, and reports that are available about these pollutants.
Ozone(O3)
(ground-level) - A colorless gas that is the major constituent of photochemical
smog.
Formed as a result of chemical reactions between
oxygen, volatile organic compounds (VOCs), and oxides of nitrogen (NOx).
Sources include vehicles, factories, landfills, industrial solvents, and
miscellaneous small sources such as gas stations, lawn equipment, etc.
Irritates the respiratory tract; produces impaired
lung function such as inability to take a deep breath; causes throat irritation,
chest pain, cough, lung inflammation, and possibly susceptibility to lung
infection; aggravates existing respiratory conditions like asthma in certain
individuals; may reduce yield of agricultural crops and injure forest and
other vegetation.
Carbon Monoxide(CO) - An odorless, colorless gas resulting from incomplete fossil
fuel combustion.
Automobiles, buses, trucks, small engines, boilers
and some industrial processes. High concentrations can be found in confined
spaces like parking garages, poorly ventilated tunnels, or traffic intersections,
especially during peak hours.
Reduces the ability of blood to deliver oxygen
to vital tissues affecting the cardiovascular and nervous systems. Symptons
include dizziness, headaches, nausea, fatigue, memory and visual impairment,
and decreased muscular control and ability to exercise.
Nitrogen Dioxide(NO2) - Causes respiratory illnesses and lung disease
and is an important component of smog.
A component of NOx (a smog-forming
chemical). Result of burning fuels in utilities, industrial boilers, automobiles,
and trucks.
Major pollutant that causes smog and acid rain.
Can harm humans and vegetation when concentrations are sufficiently high.
May cause lung damage and illnesses of breathing passages and lungs.
Particulate
Matter(PM) - Solid matter or liquid droplets from smoke,
dust, fly ash, and condensing vapors.
Result of burning of wood, diesel and other
fuels; industrial plants; agriculture (plowing, burning off fields); unpaved
roads and construction.
Causes nose and throat irritation, lung damage,
bronchitis, and possibly premature death. Children, the elderly, and people
suffering from heart or lung disease are especially at risk. Also damages
paint, soils clothing and furniture, and reduces visibility.
Sulfur Dioxide(SO2) - A colorless gas, odorless at low concentrations
but pungent at very high concentrations.
Emitted from industrial, institutional and utility
boilers; petroleum refineries, smelters, paper mills, and chemical plants.
May cause breathing problems and permanent damage
to lungs; an ingredient in acid rain which can damage trees, lakes, and
metals and reduce visibility.
Lead(Pb)
- A heavy metal which can cause adverse health effects either through ingestion
or direct inhalation.
Lead-contaminated soil, dust, paint, etc.; transportation
sources using lead in their fuels; coal combustion, smelters, car battery
plants, and combustion of garbage containing lead products.
Elevated levels can cause brain and other nervous
system damage and adversely affect kidney function, blood chemistry, and
digestion. Children are at special risk. Lead can also harm wildlife.
REGULATED TOXIC AIR POLLUTANTS (RTAPs)
Pollutant
Sources
Effects
RTAP - Includes
several volatile and non-volatile compounds with varying effects of human
health.
Emitted by a variety of industrial and
manufacturing sources
A variety of acute and chronic health effects
depending on the specific compound.
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