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An Important Issue: Relating Vegetation Experiments
with Real-World Exposures

 

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.

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