Products, Services, and Data

Air Quality

Program Overview

Note: Several air quality terms in this text are linked to their definitions on the glossary page of the air quality section.

COMPASS is involved in various studies, public education, and technical assistance to our member agencies to address the air quality issues in the Treasure Valley. For more information contact: MaryAnn Waldinger, (208) 475-2242.

The Idaho Department of Environmental Quality (DEQ) has been monitoring for the pollutant ozone (O3) since Spring 2001. In that time the Treasure Valley has had multiple exceedances of the National Ambient Air Quality Standards (NAAQS). COMPASS is working in conjunction with DEQ to educate the community on the health problems associated with ozone and with elected officials on actions that can be taken to mitigate the problem.

Air Quality Conformity Demonstration for Northern Ada County

Amendments to the Federal Clean Air Act (CAA) mandate that any future transportation projects that use federal funds and/or are deemed to be “regionally significant” in nonattainment and maintenance areas cannot contribute to a degradation of air quality (40CFR93). Thus, transportation plans must “conform” to air quality plans. Transportation conformity is demonstrated when a nonattainment or maintenance area can show, within the applicable guidelines and regulations, that planned transportation projects listed in a transportation program or plan will not cause or contribute to exceedances of the Environmental Protection Agency’s (EPA’s) health based air quality standards. A finding of nonconformance of a transportation improvement program (TIP) or plan would prevent the implementation of certain federally funded and/or regionally significant transportation projects in the TIP and/or plan. The air quality program of the Community Planning Association of Southwest Idaho (COMPASS) ensures this requirement is met.

Northern Ada County was designated as a PM10 nonattainment area in 1991. On March 12, 1999, the Environmental Protection Agency (EPA) Administrator signed a revocation of Northern Ada County’s PM10 nonattainment designation. This ruling was challenged in the Ninth District Circuit Court. On January 31, 2001, the U.S. Department of Justice approved a settlement agreement for the Idaho Clean Air Force et al. v. EPA et al. lawsuit. A major component of the settlement agreement required an update to Northern Ada County’s PM 10 State Implementation Plan (SIP). In September of 2003, the EPA approved the Northern Ada County PM 10 SIP Maintenance Plan and Redesignation. Thus, Northern Ada County is currently a maintenance area in attainment of the PM 10 NAAQS.

Northern Ada County was designated as a carbon monoxide (CO) nonattainment area in 1978. On December 27, 2002 the EPA redesignated Northern Ada County as a maintenance area for CO with the approval of a limited maintenance plan. As a result, conformity tests are not required. However, to facilitate good air quality planning and state air quality requirements, COMPASS completes a CO Planning Analysis of current transportation plans and TIPs to determine their impacts on the air quality of the region.

Learn more about air quality in an "Air Quality Conformity 101" guide.

Project Level or Hot-spot Analysis

Project level analysis assesses air quality impacts on a scale smaller than the entire non-attainment or maintenance area (for example, congested roadway intersections and highways or transit terminals), and use an air quality dispersion model to determine the effects of emissions on air quality (40 CFR 93.101). These project level studies contain estimates of likely future localized CO and PM10 pollutant concentrations and a comparison of those concentrations to the NAAQS.

The Idaho Transportation Department (ITD) currently assesses all Federal-aid transportation projects for potential impacts due to carbon monoxide. The procedures and criteria used to conduct these assessments are referred to as the “Project Level Air Quality Screening, Analysis and Documentation for Roadway Projects in Idaho” or PLAQ. The PLAQ procedures, which were developed by ITD in cooperation with the Federal Highway Administration (FHWA) and Department of Environmental Quality, were formally adopted and implemented by the State and are available on the ITD website at: