FRESNO -- In a grim announcement Wednesday, state officials said airborne soot prematurely kills up to 3,000 San Joaquin Valley residents each year, nearly triple the previous estimate.
The California Air Resources Board said a two-year public health study showed that PM-2.5, or fine-particle pollution, is 70 percent more lethal than scientists had suspected.
The study will be presented today at the state board's meeting in Fresno, where governing board members will consider approving a controversial new PM-2.5 cleanup plan for the valley.
Activists said the study is further proof that the state should delay the San Joaquin Valley Air Pollution Control District plan, which they say is not nearly aggressive enough. They said the plan should be made much tougher to protect human life.
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"Do they value 3,000 lives a year?" asked Mary-Michal Rawling, program manager of the Merced-Mariposa County Asthma Coalition. "I'm sick of hearing all the rules and excuses."
PM-2.5 specks -- about one-thirtieth the width of a human hair -- come from fires, vehicles and chemicals that combine in the air. The specks are considered more dangerous than ozone or smog.
The valley has some of the worst levels in the state, ranking alongside the South Coast Air Basin in federal PM-2.5 violations each year.
The debris is inhaled deep into the lungs, triggering asthma and other lung problems as well as contributing to heart disease. In the past decade, state officials had estimated it caused the premature deaths of more than 1,000 valley residents each year.
Based on the old estimates, a researcher at California State University, Fullerton, said the valley's annual health-related costs for PM-2.5 exceed $3 billion. Much of the cost was associated with the economic effect of losing so many people.
The new study reflects advances in medical research that have allowed scientists to better gauge the health effects of pollution.
In its study, the air resources board revised the statewide PM-2.5 mortality estimate from 8,200 annually to as many as 24,000.
Bart Croes, chief of the state air agency's research division, said the study probably could be used to help push for lower PM-2.5 health thresholds. The federal level is 15 micrograms per cubic meter.
Many scientists believe people would be safer at half that level, but it will take more research to establish a lower figure.
"We really don't know what the health-protection level is," Croes said.
In the valley, most of the PM-2.5 is created when chemicals combine in the air.
Oxides of nitrogen -- NOx -- from vehicles combine with plumes of ammonia coming mostly from dairies to form a chemical speck called ammonium nitrate, which accounts for nearly half of the region's PM-2.5.
Regional air district officials are counting on state diesel rules to reduce NOx dramati- cally by 2014, the same year the new PM-2.5 cleanup would be finished.
Diesel trucks, over which the district has little authority, are the valley's biggest source of NOx. The same pollutant helps form ozone in summer.
The district plans to tighten fireplace-burning regulations in the next two years.
Activists have suggested many other tweaks in the rules, such as replacing diesel farm water pumps with electric pumps. Officials said the suggestions are either impractical or simply do not work.