The EPA is taking final action to revise the regulatory definition of volatile organic compounds (VOCs) for purposes of preparing state implementation plans (SIPs) to attain the national ambient air quality standards (NAAQS) for ozone under title I of the Clean Air Act (CAA). This final action adds 2,3,3,3-tetrafluoropropene (also known as HFO-1234yf) to the list of compounds excluded from the regulatory definition of VOCs on the basis that this compound makes a negligible contribution to tropospheric ozone formation. As a result, if you are subject to certain federal regulations limiting emissions of VOCs, your emissions of HFO-1234yf may not be regulated for some purposes. This action may also affect whether HFO-1234yf is considered a VOC for state regulatory purposes, depending on whether the state relies on the EPA's regulatory definition of VOCs.