It is important to relate experimental
conditions with those experienced under real-world conditions.
The exposure regimes experienced under actual ambient conditions
did not match those that elicited growth reduction in the controlled
vegetation experiments on which the 1996 proposed secondary SUM06
standard was based. The data on which the 1996 proposed secondary
standard was based were derived from experiments associated with
the National Crop Loss Assessment Network (NCLAN). It was pointed
out in the peer-review literature, and acknowledged in the EPA
Criteria Document (U.S. EPA, 1996; U.S. EPA, 2006), Staff Paper,
December 13, 1996, and July 18, 1997 Federal Notices that these
experiments contained numerous hourly average concentrations
greater than or equal to 0.10 ppm near the 10% yield reduction
level, the level at which the standard was proposed. Many of
the locations across the United States that would violate the
1996 proposed vegetation standard did not experience numerous
occurrences of hourly average concentrations greater than or
equal to 0.10 ppm. This observation has been carefully integrated
into the vegetation effects projections made by A.S.L. &
Associates for the Southern Appalachian Mountain area. The Phase
I report describing the projections is available from the Southern
Appalachian Mountain Initiative (SAMI) program. Please call A.S.L.
& Associates for details on how to receive a copy of the
report.
In 2006, the EPA's Ozone
Staff Paper (EPA, 2006) recommended that the W126
exposure index be considered as a possible secondary ozone standard.
Following EPA's recommendation, in August 2006, EPA's Clean Air
Scientific Advisory Committee (CASAC) recommended that the W126
be adopted as a standard to protect vegetation from ozone exposure.
The scientific consensus was that the cumulative W126 exposure index was a more relevant metric to use
to protect vegetation than the 8-hour average health-related
exposure index. In June 2007, the EPA Administrator recommended
the W126 exposure index as a secondary standard to protect vegetation
from ozone exposure. On March 12, 2008, the EPA Administrator
made the final decision on the human health and vegetation ozone
standards. EPA revised the 8-hour "primary" ozone standard,
designed to protect public health, to a level of 0.075 parts
per million (ppm). The previous standard, set in 1997, was 0.08
ppm. Although the EPA Administrator recommended the W126 as the
secondary ozone standard, based on advice from the White
House (Washington
Post, April 8, 2008; Page D02), the EPA Administrator made the
secondary ozone standard the same as the primary 8-hour average
standard (0.075 ppm).
References
U.S. Environmental Protection Agency (1996)
Air quality criteria for ozone and related photochemical oxidants.
Environmental Protection Agency, Office of Air Quality Planning
and Standards, Research Triangle Park, NC. U.S. EPA report no.
EPA/600/P-93/004bF.
U.S. Environmental Protection
Agency (2006) Review of National Ambient Air Quality Standards
for Ozone-Assessment of Scientific and Technical Information.
Office of Air Quality Planning and Standards, Research Triangle
Park, NC. EPA/600/R-05/004af.
Washington Post (2008)
It's Not a Backroom Deal If the Call Is Made in the Oval Office
by Cindy Skrzycki. Tuesday, April 8, 2008; Page D02.
