The United States Environmental Protection Agency (USEPA) has approved a revision request for the Illinois State Implementation Plan (SIP) submitted by the Illinois Environmental Protection Agency (IEPA) to update the definition of Volatile Organic Matter (VOM), also known as Volatile Organic Compounds (VOC). The request pertained to the addition of 2, 3, 3, 3 - Tetrafluoropropene, also known as HFO-1234yf, to the list of excluded compounds that do not qualify as VOM. HFO-1234yf was excluded from the regulatory definition of VOCs per USEPA's final rule, which became effective on November 21, 2013, due to its negligible contribution to photochemical reactivity and contribution to tropospheric ozone. The USEPA has approved the IEPA's request and also published the rulemaking as a proposed and direct final rule which is tentatively set to become effective December 4, 2015 if no adverse comments are received by November 4, 2015.