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Coarse Particle Standards <br />24-hour standards <br />• EPA is retaining the current 24-hour PM10 standards to protect against health and welfare <br />effects associated with exposure to some types of coarse particles. Short-term exposure to <br />coarse particles in urban and industrial areas is associated with serious health effects. <br />Retaining this standard will provide protection in all areas of the country against the <br />effects of short-term exposure to such coarse particles. <br />Scientific evidence links health problems to coarse particle exposure in urban and <br />industrial areas, but evidence about exposure in rural areas is limited. The Agency is <br />recommending that States focus their control programs on urban and industrial sources <br />that are contributing to air quality violations. <br />• The Agency intends to characterize uncertainties in the currently available information on <br />coarse particles as part of the Agency's ongoing PM research program. <br />Annual standards <br />• EPA is revoking the annual PM10 standards, because there is insufficient evidence linking <br />health problems to long-term exposure to inhalable coarse particle pollution. <br />THE FORM OF THE STANDARDS <br />When EPA sets air quality standards, it also must specify the air quality statistics that the <br />Agency will use to determine whether an area is meeting the standards. These statistics are <br />known as the "form of the standard" and are derived separately for each standard. <br />Fine particles —form of the 24-hour standard <br />• An area will meet the 24-hour standard if the 98th percentile of 24-hour PM2.5 <br />concentrations in a year, averaged over three years, is less than or equal to the level of the <br />standard of 35 gg/m3. This is the same form as the current 24-hour standard. <br />Fine particles —form of the annual standard <br />• An area will meet the annual PM2.5 standard when the three-year average of the annual <br />average PM2.5 concentration is less than or equal to 15 gg/m3. This is the same form as <br />the current annual standard. <br />The revisions limit the conditions under which some areas may average measurements <br />from multiple community -oriented monitors to determine compliance with the annual <br />standard. <br />