The East Bay communities actually experienced a reduction in ozone pollution from 1991. The Bay Area has had persistently better air quality than other regions in the state, despite a significant increase in the number of days in which pollutants have exceeded federal and state standards starting in 1995. Air currents carry much of the pollution away from the Bay Area and recent El Nino and La Nina weather patterns have helped reduce ozone concentrations.
Air pollution is caused largely by motor vehicles.
The problem is magnified by the increasing distances that people are commuting each day. Although public transit systems are gaining popularity, automobile traffic congestion continues to increase.