In 2001, the four-county South Coast Air Basin experienced 36 days exceeding the federal one-hour ozone standard, followed by 45 days in 2002 and 64 days in 2003.
Although air quality may be improving, Southern California is still failing to meet federal standards, which are becoming tougher due to growing knowledge about the dangers of air pollution, critics note.
The Environmental Protection Agency this year announced that by 2021 cities will have to meet the ozone standard that measures the pollutant in the air over an eight-hour span. It requires levels to remain below .08 ppm.
So far this year, the South Coast area has violated that standard on 86 days -- roughly a third of the time. The San Joaquin Valley, which is expected to have a harder time meeting the eight-hour standard because its pollution lingers longer, has exceeded it on 97 days so far this year.
Although ozone has been the barometer used to measure air pollution in California, air-quality experts are increasingly concluding that particulate matter -- microscopic specks commonly released into the air by car, truck and ship exhaust -- may be more dangerous.
A recent USC study that tracked Southern California children from fourth grade until they graduated from high school found that children growing up in polluted areas were more likely to have underdeveloped lungs, leading to a lifetime of possible health problems.