Figure 1. Kaiser Permanente Northern California (KPNC) study region and 2007 1‐year average fine particulate matter <2.5 µm in diameter (PM2.5) levels.
The KPNC study region includes 35 counties: Alameda, Amador, Butte, Calaveras, Colusa, Contra Costa, El Dorado, Fresno, Glenn, Kings, Lake, Madera, Marin, Mariposa, Mendocino, Merced, Monterey, Napa, Nevada, Placer, Sacramento, San Benito, San Francisco, San Joaquin, San Mateo, Santa Clara, Santa Cruz, Solano, Sonoma, Stanislaus, Sutter, Tulare, Tuolumne, Yolo, and Yuba.