SACRAMENTO (AP) — While overall air quality in California has improved significantly over the past decade, about a third of the population lives where pollution is in excess of federal health standards, according to state officials.

The California Air Resources Board presented an assessment of smog and soot levels on Thursday in Sacramento, the Los Angeles Times reported.

The board's report said smog fell 15 to 20 percent in urban areas since 2003, yet levels remain above federal health standards in parts of greater Los Angeles, the San Joaquin Valley, Sacramento and San Diego.

In the South Coast region, which includes Los Angeles and Orange counties, the number of high-ozone days has dropped 21 percent since 2003. State officials now estimate about 60 percent of people, including all coastal residents, live where smog meets federal health standards. But 6 million people in inland areas still live with unacceptably smoggy air, officials said.

Of the state's five biggest urban areas, only the San Francisco Bay area meets all federal standards for ozone — the worst component of smog — and fine particulate matter, or soot, according to the assessment.

Air board officials took no action after hearing the staff report.

The evaluation came as exceptionally dry and stagnant weather this winter has worsened air pollution across California and the Southwest, with some of highest levels in the Central Valley, the Times said. Officials said continuing spells of bad air could set the state back.

"I don't think we should be too congratulatory because this year has been a bad year," said board member John Balmes, a professor of medicine at UC San Francisco.

Health studies link ozone and fine-particle pollution to respiratory illness and other health problems, including asthma, heart disease and cancer.

Curbing smog over the next decade will require big cuts in nitrogen oxides and volatile organic compounds, according to the board's report. Those gases — emitted by vehicles, factories and power plants — react in the air to form ozone and fine particles.

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