New major and modified existing stationary sources require air permits prior to beginning construction. Where increases of criteria pollutants such as sulfur dioxide, nitrogen dioxide, carbon monoxide, particulate and volatile organic compounds exceed a “significance” threshold, the permittee is required to analyze available and technically feasible control technology with the goal of selecting the best available control technology (BACT) for new or modified emissions units. With agency agreement, the selection of BACT becomes an enforceable part of the permit.
We now have a new “pollutant,” greenhouse gas (“GHG”) equivalents for the six regulated greenhouse gases (carbon dioxide, methane, nitrous oxide, sulfur hexafluoride, perfluorocabons, and hydrofluorocarbons). GHGs are measured as equivalents to carbon dioxide, the most common GHG (CO2e). Starting January 2, 2011, permits issued for facilities that otherwise trigger PSD (as above) and have a new or increased potential to emit (PTE) of CO2e of 75,000 TPY, must address GHG emissions. Following July 1, 2011, a PSD permit may be required for significant increases in GHGs alone (100,000 tpy for a new source or 75,000 tpy for` a modification), even where there is no significant increase of any other regulated criteria pollutant.
As with other pollutants, once PSD is triggered for GHGs, the permittee must evaluate and propose that which constitutes BACT to control the CO2e. Although the general scheme for selecting BACT is familiar, a top down ranking of available and technical feasible technologies, the available options are not. There are no conventional CO2e scrubbers or waste heat boilers, or filter traps to capture CO2e. While some technologies are emerging, the process of determining BACT for CO2 control is a new frontier, and lack of guidance can cause permitting delays. To address some of the uncertainties, EPA issued guidance on November 10, 2010 concerning permitting GHGs explaining the process for determining the required emission control technology – BACT.