SACRAMENTO -- Southern Californians are breathing significantly cleaner, healthier air than ten years ago because of the state's aggressive anti-smog program, according to an Air Resources Board (ARB) review of monitoring data.

According to the ARB analysis, the annual amount of unhealthy air pollution-declined 50 percent in the South Coast Air Basin, home to one-third of the state's population, between 1981 and 1991. During the same time, the highest, peak urban smog (ozone) levels were reduced 25 percent.

The ARB analysis also noted that the air quality improvements were not confined to any one area, but were documented throughout the basin from the coast to the desert.

"Contrary to trends in some other parts of the country, these figures speak for themselves and show that California's effort to improve air quality is well-founded scientifically and is making more progress than other regions of the country," said James D. Boyd, ARB executive officer in releasing the study.

Boyd noted that the ARB reviewed air quality data over a decade to isolate the real effect of the state's anti-smog program from meteorology that can strongly influence smog levels from one year to another.

An average of top hourly ozone readings dropped from 0.33 parts per million (ppm) to 0.25 ppm compared to a decade ago and a state health standard of 0.09 ppm. A composite look at smog levels throughout the coastal cities found they experienced about 200-400 hours a year of ozone levels above that health standard, about 50 percent less than a decade ago. Inland areas ranged from 600-800 hours per year of excessive ozone, down about 50 percent over the last ten years and reduced even more from a peak of about 1,800 hours in 1984.

Boyd noted that the ARB's program not only requires the world's cleanest cars and fuels -- while local air pollution control districts adopt the nation's strictest emission limits for industrial facilities -- but also attacks both of the basic chemical compounds that form urban smog by setting standards for both hydrocarbon and nitrogen oxides.

"A National Research Council report earlier this year that faulted anti-smog programs in other states and called for more control of nitrogen oxide emissions actually endorsed the philosophies that we have had in California for decades," said Boyd. "While we have a ways to go before we meet health standards in Southern California, this marks the second strong report card we've had in the last five years and shows that we are on the right track toward significantly cleaner air in the area with the nation's biggest urban smog problem."

The ARB's review of smog trends comes on the eve of a technical conference to review findings of the largest air quality research project ever conducted in Southern California. The Southern California Air Quality Study, of which the ARB was a major sponsor, used 50 teams of researchers to study emission patterns, meteorology, and the chemistry of urban smog formation to upgrade understanding of the region's complex pollution problem.

After five years of evaluating billions of pieces of scientific information, researchers will present some of their findings during a series of technical discussions to be conducted July 21-23, at the Sunset Village Conference Center on the campus of UCLA.