Sierra Club petitions the Environmental Appeals Board (“Board”) to review a Clean Air Act prevention of significant deterioration (“PSD”) permit regulating greenhouse gas (“GHG”) emissions that the United States Environmental Protection Agency (“Agency”) Region 6 (“Region”) issued to ExxonMobil Chemical Company (“Exxon”) on November 25, 2013. The Final Permit authorizes Exxon to construct a new natural gas-fired ethylene production unit (“Facility”) at Exxon’s existing Baytown Olefins Plant in Harris County, Texas.