This rule promulgates national emission standards for hazardous air pollutants (NESHAP) for new and existing plant sites that manufacture polyether polyols. The hazardous air pollutants (HAP) emitted by the facilities covered by this rule include ethylene oxide (EO), propylene oxide (PO), hexane, toluene, and incidental emissions of several other HAP. Some of these pollutants are considered to be probable human carcinogens when inhaled, and all can cause toxic effects following exposure. The rule is estimated to reduce emissions of these pollutants by 1,810 Megagrams per year (Mg/yr) (2,000 tons per year (tons/yr)). Because all of the pollutants are also volatile organic compounds (VOC), which are precursors to ambient ozone, the promulgated rule will also aid in the reduction of tropospheric ozone.