PM10 Nonattainment Area

The U.S. Environmental Protection Agency (EPA) designated Missoula, Montana as a moderate nonattainment area for the 24-hour NAAQS for particulate matter with an aerodynamic diameter less than or equal to a nominal 10 micrometers (PM10) upon enactment of the federal Clean Air Act Amendments of 1990 (56 FR 56694, November 6, 1991).

The nonattainment classification was based on violations of the 24-hour standard that occurred throughout the 1980s. The EPA fully approved Montana’s moderate PM10 nonattainment area plan as a State Implementation Plan (SIP) revision for the Missoula PM10 nonattainment area in 1995 (60 FR 45051).

There has been no measured violation of EPA’s PM10 standard since 1989.

The boundary for the Missoula County PM10 nonattainment area is defined as follows:

T13N, R19W, Sections 2, 8, 11, 14, 15, 16,17, 19, 20, 21, 22, 23, 24, 27, 28, 29, 30, 31, 32, 33, and 34; T12N, R19W, Sections 4, 5, 6, and 7; T13N, R20W, Sections 23, 24, 25, 26, 35, and 36.

This area essentially includes the City of Missoula and surrounding area in Missoula County.


CO Maintenance Area

As a result of the 1977 amendments to the Clean Air Act (CAA), Missoula was designated nonattainment for carbon monoxide (CO) by the U.S. Environmental Protection Agency (EPA) in the Federal Register (FR) notice (43 FR 9010) on March 3, 1978.  The National Ambient Air Quality Standard (NAAQS) for CO is 9 parts per million (ppm) for an 8-hour average concentration, not to be exceeded more than once per calendar year.  Missoula’s violations of the CO NAAQS were attributed primarily to motor vehicle emissions and residential wood combustion.  The community took several steps to reduce the ambient levels of CO, including reconfiguring traffic intersections to relieve congestion and implementing rules to limit emissions from residential wood combustion and outdoor burning.  Missoula continued to violate the NAAQS until the early 1990s. 

Following the promulgation of the Clean Air Act Amendments of 1990, EPA classified Missoula as a moderate nonattainment area for CO (56 FR 56694) based on a design value of 9.7 for 1987 through 1989.  This designation required Missoula to develop a new base year inventory for 1990 and establish an oxygenated fuel program by November 1992.  In June 1992, Missoula incorporated an oxygenated fuels program into the Missoula City-County Air Pollution Control Program.  It was approved by the Montana Board of Environmental Review (BER) in September 1992, and implemented that November.  On November 6, 1992, the Governor of Montana submitted the oxygenated fuels program to EPA for approval.  Since implementing the oxygenated fuels program, Missoula has not violated the CO NAAQS. 

There have been several SIP updates since Missoula was first declared nonattainment for CO.  The EPA approved the Missoula CO nonattainment area plan on January 16, 1986 (51 FR 2397). Subsequent revisions were approved on November 8, 1994 (59 FR 55585) regarding the oxygenated gasoline program in Missoula; December 13, 1994 (59 FR 64133) regarding CO contingency measures; December 6, 1999 (64 FR 68034) regarding an update to the SIP narrative; and November 15, 2001 (66 FR 57391) regarding revisions to the Missoula Air Pollution Control Program that included extensive renumbering, reorganization and rule revisions. 

In 2005, the Missoula City-County Health Department developed a redesignation request and maintenance plan for CO with guidance based on the 1990 amendments to the CAA and a September 4, 1992 EPA memo from John Calgani to the EPA Regional Air Directors.  The Governor of Montana submitted the redesignation request to EPA on May 27, 2005, and EPA approved it in an FR notice on August 17, 2007 (72 FR 46158).  The redesignation request addressed the five criteria required by Section 107(d)(3)(E) of the CAA, as follows:

 Criterion 1:  Attainment of the Applicable National Ambient Air Quality Standard

Criterion 2:  State Implementation Plan Approval

Criterion 3:   Permanent and Enforceable Improvements in Air Quality

Criterion 4:  Fulfillment of CAA Section 110 and Part D Requirements

Criterion 5:  Fully Approved Maintenance Plan under CAA Section 175A

The 2005 Missoula CO Redesignation Request included a full maintenance plan as required by the CAA for moderate nonattainment areas.  However, CO levels in Missoula have dropped precipitously since the area was classified as a “moderate” nonattainment area.  Between 2006 and 2011 (the most recent 5 years of CO data), the maximum CO 8-hour concentration was 4.1 ppm – well below the NAAQS. 

The Missoula CO maintenance area includes the following (Range and Township) sections: R19W T14N – sections: 29 and 32; R19W T13N – sections: 2, 5, 7, 8, 11, 14 through 24, and 26 through 34; R19W T12N – sections: 4 through 7; R20W T13N – sections: 23 through 26, 35 and 36. 

This area essentially includes the City of Missoula and some surrounding area in Missoula County.