Regulating Air Pollution under the Clean Air Act
The Clean Air Act requires EPA to protect air quality and directs different approaches to
address different types of air pollution. Here we will look at "hazardous" and "common" air
pollutants.
Hazardous (or Toxic) Air Pollutants
Ethylene oxide is a hazardous air pollutant, which is also referred to as a toxic air pollutant.
There are 187 different toxic air pollutants regulated by EPA. They are known to cause
cancer and other serious health impacts such as reproductive effects or birth defects. EPA
does not set ambient standards for these pollutants, but rather develops standards
specifically for those industrial facilities that emit them in two phases.
•	The first phase is "technology-based." EPA develops emissions standards for
controlling air toxics from sources in an industry group (or "source category").
These emissions standards, called maximum achievable control technology (MACT)
standards, are based on emissions levels that are already being achieved by the
best-controlled and lowest-emitting sources in an industry. EPA has completed this
initial phase of emission limitations for almost all listed source categories.
•	The second phase is "risk-based." Within 8 years of setting the MACT standards, the
Clean Air Act directs EPA to assess the remaining health risks from each source
category to determine whether the MACT standards protect public health with an
ample margin of safety and protect against adverse environmental effects. In this
phase, called residual risk, the EPA must determine whether more health-protective
standards are necessary.
o Also, every 8 years after setting the MACT standards, the Clean Air Act
requires that the EPA review and revise the MACT standards, if necessary, to
account for improvements in air pollution controls and/or pollution
prevention.
EPA is reviewing Clean Air Act regulations for facilities that emit ethylene oxide:
•	EPA has begun reviewing its emissions standards for miscellaneous organic
chemical manufacturing facilities, some of which emit ethylene oxide.
•	The Agency also plans to take a closer look at its rules for other types of facilities
that emit ethylene oxide, beginning with its emissions standards for commercial
sterilizers.
EPA is also getting additional information on ethylene oxide emissions
•	EPA is gathering additional information on industrial emissions of ethylene
oxide, which may include data from testing at facilities.
•	This information will help EPA as it looks for opportunities to reduce ethylene
oxide emissions as part of its regulations review.
•	It also will help us determine whether more immediate emission reduction steps
are necessary in any particular locations.

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Common Air Pollutants
EPA takes a different approach for regulating common air pollutants. The Agency sets
health-based outdoor air quality standards known as National Ambient Air Quality
Standards (NAAQS) for six common air pollutants. These pollutants, also known as criteria
pollutants include ozone, particle pollution, oxides of nitrogen, sulfur dioxide, lead and
carbon monoxide. They are found all over the U.S. and can harm your health and the
environment, and cause property damage. EPA works closely with state, local and tribal
environmental agencies to monitor outdoor air quality for these pollutants, and limit
emissions as needed to assure these standards are not exceeded.
Compliance with Air Pollution Controls
Sources must get Clean Air Act operating permits from the appropriate permitting
authority, which is generally the state air agency. These permits list requirements to
control air pollution that apply to a source. Sources must comply with these permits or
face penalties.
How can I submit questions?
Email your questions to: eto@epa.gov
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