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EPA Advances Cooperative Federalism Through Designation Process for Sulfur Dioxide and Ozone Standards

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WASHINGTON (December 22, 2017) – The U.S. Environmental Protection Agency (EPA) is taking the next steps in the Clean Air Act process to determine which areas of the country meet national air quality standards for ground-level ozone and sulfur dioxide. In November 2017, the Agency designated the vast majority of U.S. counties as meeting the air quality standards set by EPA’s 2015 National Ambient Air Quality Standards (NAAQS) for ozone. EPA is responding to state and tribal recommendations for ozone designations for the remaining areas and providing additional opportunities for state, tribal, and public input on those areas’ designations. The Agency is also finalizing designations for certain areas for the 2010 sulfur dioxide NAAQS.

“Cooperative federalism is key to maintaining clean air,” said EPA Administrator Scott Pruitt. “Largely due to work by the states and new technological advances by the private sector, monitored levels of SO2 have dropped 85 percent and levels of ozone have decreased 22 percent nationwide since 1990. I am encouraged by the progress we’ve made and will continue working alongside states, tribes, and localities to determine the best methods to meet air quality standards.”

This action on sulfur dioxide is the third of four rounds of final designations. These designations reflect progress for sulfur dioxide, as only six areas have been designated “nonattainment” with the 2010 standard. Only 50 areas remain to be designated for sulfur dioxide in the fourth and final round. For these areas, EPA is supporting the decision by states to install and operate new monitors, so they can gather three full calendar years of data to inform a designation by the end of 2020. Additional information on this action is available at:

With respect to ozone standards last updated in 2015, EPA today, in accordance with the Clean Air Act, sent letters to states to start a 120-day period for states and tribes to provide more information with regard to their suggested designations of certain areas where further analysis and dialogue may be needed. While not required to seek public comment during the 120-day period, EPA will also be opening a 30-day comment period for the public to provide input on these designations before they are finalized. The Agency acknowledges the importance of background ozone outside the control of state and tribal air agencies. These designations employ the limited tools for regulatory relief for state and tribal air agencies to address background ozone, including: the exclusion of data that result from ‘exceptional events,’ the use of rural transport areas, and appropriately tailored nonattainment area boundaries for sites minimally impacted by nearby sources. EPA looks forward to working with its state, local, and tribal government partners to fulfill the Congressional design of protecting public health through cooperative federalism. Additional information on this action is available at: