The U.S. EPA originally proposed a separate ozone standard (i.e., SUM06) to protect vegetation. In July 1997, the Agency decided not to adopt such a standard. The EPA believed that the 8-hour ozone standard adopted to protect human health would be adequate to protect vegetation. The important question to answer is whether achieving the 8-hour standard will protect adequately crops and trees. Using 1993-1995 data, we estimated that 55 out of 186 areas (approximately 30%) would have violated the SUM06 vegetation standard but not violate the 8-hour ozone standard. A map describing the violating areas for the SUM06 exposure index can be viewed. Thus, approximately 70% of the areas that would violate the SUM06 proposed vegetation standard would have violated the 8-hour standard. Further analysis is showing that the relationship between the form of the 8-hour standard and biologically relevant exposure indices used to predict possible vegetation effects is not statistically strong.

Do we need a separate standard to protect vegetation? Is the 8-hour ozone standard protective enough for vegetation? Our research is continuing in this important area. Several federal agencies are using the W126 exposure index on a national level to protect vegetation from injury and damage. In 2000, the Federal Land Managers Air Quality Related Values Workgroup (FLAG) adopted the use of the W126 exposure index. Many of the federal air quality experts in the U.S. Forest Service are applying the index for assessing the possible deleterious effects associated with ozone exposures. In June 2007, the EPA Administrator proposed the W126 exposure index as the secondary ozone standard. 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. EPA decided not to adopt the W126 exposure index. 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). For more information about the W126 exposure index, please click here.