Air Quality Frequently Asked Questions


 How Bad is the Region's Air Quality?

The U.S. Environmental Protection Agency has designated the Sacramento region as a "severe ozone non-attainment area," including all of Sacramento County and parts of El Dorado, Placer, Solano, Sutter, and Yolo counties. During the summer, our region often fails to meet both the state and federal health-based standards for ozone.

What Causes Poor Air Quality?

Nestled between the mountains, the Sacramento Valley is shaped like a long, oval bowl. When an inversion layer traps pollutants close to the ground, air quality becomes unhealthy.

What is "Conformity"?

In order for a transportation plan to be approved by the federal government, the plan must be consistent with the state's obligation to meet federal air quality standards. The Sacramento region is currently designated as a "non-attainment" area by the U.S. Environmental Protection Agency (EPA), meaning that our geographic area does not meet the National Ambient Area Quality Standards for one or more regulated pollutants.

The 1990 Clean Air Act requires a "transportation conformity" provision to ensure that a state does not undertake federally-funded or approved transportation projects, plans, or programs that could prevent the region from meeting federal air quality standards. This conformity regulation states that in order to gain federal approval for plans, metropolitan planning organizations such as SACOG, in non-attainment areas must develop forecasts of traffic and emissions for a 20-year horizon. The forecasts of emissions must be no greater than the amount of emissions allowed by federal law.