Document ID: EPA-HQ-OAR-2005-0172-7155
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2008-03-12T04:00Z

Ozone Secondary NAAQS

Options are to set a secondary National Ambient Air Quality Standard
(NAAQS) for ozone:

that accumulates over the course of a season (called a “seasonal
form”) and at a level generally less stringent than the primary
standard or 

that averages over the course of 8 hours and at a level equal to the
primary standard.

Legal Background

The primary ozone standard protects people. The secondary ozone standard
protects welfare such as sensitive ecosystems and forests.

The Clean Air Act requires a secondary NAAQS that, in the
Administrator’s judgment, “is requisite to protect the public
welfare from any known or anticipated adverse effects associated with
the presence of such air pollutant in the ambient air.”

“Welfare” includes effects on soils, water, crops, vegetation,
manmade materials, animals, wildlife, weather, visibility and climate,
damage to and deterioration of property, and hazards to transportation,
as well as effects on economic values and on personal comfort and
well-being.

“Welfare” does not include the consideration of costs. “EPA may
not consider implementation costs in setting primary and secondary
NAAQS.” Whitman v. American Trucking Assns., Inc., 531 U.S. 457, 486
(2001).

EPA must complete its multi-year review of the ozone standard by issuing
a final decision tomorrow.

Criteria Document in March 2006

Staff Paper in January 2007

Proposal in June 2007

Option selection in January 2008



The seasonal form is the most scientifically defensible. Ozone decreases
the ability of plants to produce and store food. The impact of repeated
ozone exposure accumulates over the course of the growing season. Key
scientific uncertainties have been substantially addressed since the
last review in 1997. The new evidence includes a broader array of
vegetative effects and a diverse set of research studies looking at the
effects of ozone in the real world.

The Administrator’s decision is consistent with scientific advice.

The National Academy of Sciences (NRC 2004) stated “[w]hatever the
reason that led EPA to use identical primary and secondary NAAQS in the
past, it is becoming increasingly evident that a new approach will be
needed in the future.  There is growing evidence that the current forms
of the NAAQS are not providing adequate protection to sensitive
ecosystems . . .”

The National Park Service stated there is “abundant evidence that it
is appropriate to establish an alternative cumulative secondary standard
for ozone” and that “a seasonal, cumulative metric is needed to
protect vegetation.”

All 23 members of the Clean Air Scientific Advisory Committee
recommended a form “substantially different from the primary ozone
standard.” (Henderson, 2007)

EPA staff paper recommended that the secondary standard “should be
defined” in terms of a “cumulative seasonal form.”

The USDA Agricultural Air Quality Task Force recognized that “[o]f
particular concern are the chronic effects [on plants].”

The Administrator must decide how best to set the secondary standard and
a seasonal form is the most legally defensible. By definition, the
primary and secondary standards are separate legal actions based on
separate criteria. There is no presumption that the secondary standard
should be the same as the primary standard. EPA has extensive record
support for a seasonal form and lacks scientific support for an 8 hour
form.

The Administrator proposes to establish a secondary standard with a
seasonal form and at a level generally less stringent than the primary
standard. This choice is generally not expected to require additional
controls beyond those required by the primary standard. 

We are seeking legislative amendments to modernize both the primary and
secondary NAAQS programs.

Deliberative and Confidential	

March 11, 2008

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