The federal government sets standards for the maximum amounts of different types of pollution that can be in the air before it is considered unhealthy to breathe. If an area has violated the standards, then it must have a plan in place to reduce air pollution to below the standards, and keep it there.
Northern Ada County violated the standards for coarse particulate matter (airborne dust and other particles; referred to as “PM10”) and carbon monoxide in the 1980s and early 1990s, and has been in compliance ever since. The Idaho Department of Environmental Quality has developed the required “maintenance plans” that show how Northern Ada County will maintain compliance with the standards for PM10 and carbon monoxide.
As part of that process, transportation projects that use federal funds or are “regionally significant” in areas that have violated air quality standards, such as Northern Ada County, must be part of an air quality conformity demonstration to verify that they will not degrade air quality beyond limits set in the plans.
For PM10, the maintenance plan includes pollution “budgets” for PM10 itself, as well as for pollutants that can combine to create PM10. The conformity demonstration must show that the transportation projects will not cause the region to exceed those pollution budgets. For carbon monoxide, the process is different – COMPASS compares the emissions that would be emitted if the projects were built against emissions that would be emitted if they were not.
It is important to note that Communities in Motion only plans for ground transportation; it does not include air transportation. Therefore, emissions related to air travel are not part of this demonstration.