(a) The Governor of the State of Montana submitted the 1990 carbon monoxide base year emission inventories for Missoula and Billings on July 18, 1995, as a revision to the State Implementation Plan (SIP). The Governor submitted the 1990 carbon monoxide base year emission inventory for Great Falls on April 23, 1997, as a revision to the SIP. The inventories address emissions from point, area, on-road mobile, and non-road sources. These 1990 base year carbon monoxide inventories satisfy the nonattainment area requirements of the Clean Air Act of section 187(a)(1) for Missoula and section 172(c)(3) for Billings and Great Falls.

(b) As part of the Thompson Falls Air Pollution Control Plan (approved at § 52.1370(c)(60)), the Governor of Montana submitted a PM-10 emission inventory for the Thompson Falls area as a SIP revision. The PM-10 emission inventory covers the time period of July 1, 1990 through June 30, 1991.