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Agency was aware of new science before setting the final standards. That assessment did not <br />materially change EPA's understanding of PM. EPA did not base its decision on these new <br />studies, however, because they have not been through as rigorous a level of review as the <br />science on which the Agency based its December 2005 proposal. EPA will consider these <br />new studies during the next review of the PM standards. <br />EPA has issued rules that will help states meet the standards by making significant strides <br />toward reducing fine particles. These rules include the Clean Air Interstate Rule to <br />dramatically reduce and cap particle pollution -forming emissions from power plants in the <br />eastern United States, the Clean Diesel Program to dramatically reduce emissions from <br />highway, nonroad and stationary diesel engines, and the Clean Air Visibility rule, which will <br />reduce emissions affecting air quality in national parks. <br />THE FINAL STANDARDS <br />For both fine and coarse particles, EPA sets two types of standards: primary standards, to <br />protect public health; and secondary standards, to protect the public welfare from effects <br />including visibility impairment, damage to building and national monuments, and damage to <br />ecosystems. <br />Fine Particle Standards <br />• EPA has two primary standards for fine particles: an annual standard, designed to protect <br />against health effects caused by exposures ranging from days to years; and a 24-hour <br />standard, designed to provide additional protection on days with high peak PM2.5 <br />concentrations. <br />24-hour standards <br />o Primary -- EPA has substantially strengthened the primary 24-hour fine particle standard, <br />lowering it from the current level of 65 micrograms per cubic meter (gg/m3) to 35µg/m3. <br />EPA based this decision on an assessment of a significantly expanded body of scientific <br />information. The assessment concluded that the standard should be strengthened to better <br />protect the public from the health effects associated with short-term fine particle <br />exposures. <br />o Secondary -- The Agency has set the secondary standard at the same level as the primary <br />standard (35µg/m3). <br />Annual standards <br />o Primary -- EPA is retaining the primary annual standard at 15µg/m3 based on its <br />assessment of several expanded, re -analyzed and new studies that have increased the <br />Agency's confidence in associations between long-term PM2.5 exposure and serious <br />health effects that were documented in the prior review. The assessment concluded that <br />this standard continues to be appropriate to protect the public from heath effects <br />associated with long-term fine particle exposures. <br />Secondary -- The Agency has set the secondary standard at the same level as the primary <br />standard (15µg/m). <br />2 <br />