One of the most controversial aspects of permitting as it relates to regulation of GHGs is the
number of sources that might be affected. The CAA identifies specific threshold emission
quantities (tons per year), but GHG pollutants typically are emitted in greater quantities than
‘‘traditional’’ pollutants already regulated under the CAA. So it appears that a much larger
class of emitters would be included. Tens of thousands of large office and apartment buildings,
hospitals, commercial facilities, and other emitters could exceed this threshold every
year, raising costs for sources and creating an administrative dilemma for regulators. EPA
sought to address this issue in its ‘‘Tailoring Rule,’’ which restricts permit requirements,