Data indicates that approximately 27 percent of the total air pollution in the northern portion of the District comes from the Bay Area. In the central portion of the District, the percentage drops to eleven and in the southern area, transport air pollution constitutes nine percent of the total air pollution inventory. The Valley is particularly vulnerable to air pollution formation because of its topography, climate, and growing population. Surrounding mountains trap airborne pollutants near the Valley floor where people live and breathe. Finally, as population levels increase, so does air pollution.
More people equals more cars and more activities that contribute to poor air quality.
The program works by notifying Valley residents in advance of days when air quality is forecast to reach unhealthy levels. These are designated Spare the Air days. The District notifies the public via television, radio, newspaper, and at participating worksites. When a Spare the Air day has been called, residents are asked to reduce or avoid activities that cause air pollution for the following 24 hours. Based on previous years, there are about 25 Spare the Air days per season.