In the past, DEQ managed air quality based on political boundaries. We looked at the impact of air pollution on public health within particular cities or counties. Today, DEQ is working toward managing air quality consistently across entire airsheds, which may encompass several cities and counties.

An airshed is an area covered by a volume of air that has similar characteristics and is separated from other volumes of air by weather patterns or topography.

Air pollution is not contained within political jurisdictions. Air pollution that is emitted in one area can spread out across political boundaries into adjacent cities and counties within the airshed. For this reason, air pollution levels are generally similar across a given airshed.

Airshed management has two basic components. One is to collect accurate data and develop a good scientific understanding of the air pollution dynamics in each airshed. This will ensure that any proposed strategies to manage pollution will be effective. The other is to engage the community, residents, and businesses of the airshed in decisions about the best course for protecting air quality. The communities in an airshed will be involved in establishing an air quality vision and goals for their area.

DEQ bases the boundaries of local airsheds on meteorological data from time periods when air is least able to mix and air pollution levels are expected to be highest. Monitoring and modeling data scientifically document that the Treasure Valley is a single airshed consisting of Ada and Canyon Counties; portions of Owyhee, Elmore, Gem, and Payette Counties; and portions of Oregon. To facilitate development of the airshed management approach, DEQ has limited its initial definition of the Treasure Valley to Ada and Canyon Counties. As additional data become available and outreach efforts are expanded, this definition may be modified.

In September 2001, DEQ published the Strategy for the Development of an Airshed Management Program for the Treasure Valley, which provides an overview of DEQ's airshed management initiative for managing air pollution. It explains the basic tenets of airshed management, describes the reasons why DEQ believes the airshed management approach is necessary in the Treasure Valley, and provides a framework for the development of a comprehensive airshed management program. In addition, it includes a five-year schedule for developing a document to fully detail the Treasure Valley Airshed Management Program.