District 3 covers a jurisdictional region of eleven counties within the Sacramento Valley and Sierra Nevada Mountains. Within this region various elements play an important role in respect to regional air quality. Population and growth, transportation, industry and agriculture, as well as seasonal temperatures and topography are all elements that contribute to the regions air quality.

The major pollutants in the atmosphere that contribute to poor or unhealthy air quality originate from sources such as cars, boats, trains, aircraft, farm and construction equipment, fireplaces, and industrial facilities, just to name a few. The major pollutants of concern that come from these sources are: 1) Ozone, 2) Particulate Matter, and 3) Carbon Monoxide.

• Ozone (O3) an odorless and colorless gas that is the main componenet of smog. Ozone forms through reactions involving nitrogen oxides (NOx) and reactive organic gases (ROG) in the presence of heat and sunlight. Ozone is most commonly at its peak levels during the summer months.

• Particulate Matter (PM) dust, soot, smoke and liquid droplets directly emitted into the air by transportation sources, factories, power plants, construction activity, fires and windblown dust. Particulate Matter is commonly referred as PM 10 (coarse) and PM 2.5 (fine) dust particles.

• Carbon Monoxide (CO) a colorless gas emitted when fuels are burned in engines, fireplaces and other combustion sources.

In transportation planning, air quality and transportation go hand in hand. In order for transportation projects to move forward, regional agencies such as the Butte County Association of Governments (BCAG), Sacramento Area Council of Governments (SACOG), and the Tahoe Regional Planning Agency (TRPA), must have "conforming" Regional Transportation Plans (RTP) and Transportation Improvement Programs (TIP). Conformity is a process that ensures that a RTP, or its funding source which is commonly referred to as the TIP, are not exceeding air quality standards that are set forth in the regional air quality planning documents which is known as the State Implementation Plan (SIP). If a region is exceeding set standards for the sources listed above then that region is said to be in non-attainment.

Much of the District is designated as non-attainment areas. A complex structure of jurisdictions and planning organizations are continuing to work together to formulate workable air quality attainment plans and are contributing to the State Implementation Plan (SIP), while simultaneously producing and implementing transportation plans and programs which further regional, statewide, and Federal transportation goals.

The District is a principal participant in this process primarily based on the following:

• Owner and operator of the State Highway System (SHS). Maintenance, operation, and expansion of the State Highway System are all impacted by air quality plans and programs.

• Pursuant to Federal Highway Administration (FHWA) direction, Caltrans reviews, comments and, when appropriate, recommends approval for the air quality conformity determinatios for the Metropolitan Transportation Plan (MTP), MTP amendments, the Metropolitan Transportation Improvement Program (MTIP), and MTIP amendments.