Modesto and Merced still are among the 25 cities in the United States with the most smog. But the brown stuff wasn't as thick from 2004-06, which moved the two cities down the national list.
Modesto went from 13th to 21st on the list, according to the American Lung Association's State of the Air 2008 report, released today. Merced dropped from sixth to 17th.
The Los Angeles area was the smoggiest, followed by Bakersfield, Visalia and Houston. Fresno and Sacramento were fifth and sixth, respectively.
The nation's oldest voluntary health organization issues the report card every year to call attention to the health hazards of breathing dirty air and to let people know which places in the United States have the least pollution.
Air pollution is known to cause serious health effects, especially in children, seniors and people with asthma, chronic bronchitis, emphysema, heart disease and diabetes. Ozone pollution, or smog, has a corrosive effect on the lungs and causes irritation leading to coughing, wheezing and chest pain.
A second type of air pollution consists of soot, ash and chemicals that come from diesel- engine exhausts, residential fireplaces and agricultural burning. Breathing in the tiny particles over time, lungs become clogged like a home air filter that hasn't been cleaned in years, said Dr. Tony Gerber, an association volunteer and pulmonary specialist with the University of California at San Francisco Medical Center.
Cities and counties in California usually dominate the lung association's bad air lists. But there are exceptions. Santa Barbara and the counties of San Luis Obispo, Santa Cruz, Santa Mateo and San Francisco are given credit for having some of the freshest air in the country.
Pittsburgh became the first city outside California to top one of the "most-polluted" lists in the annual report. It overtook Los Angeles as the place with the worst short-term particle pollution.
"We see improvements in some areas of the state, but the levels of ozone and particle pollution in California remain dangerously high," said Gwendolyn Young, board chairwoman of the American Lung Association. "Improvements don't mean the problem is solved."
Stanislaus, Merced and San Joaquin counties still received failing grades for smog and pollution caused by tiny soot particles.
According to the report, which looked at data from 2004 to 2006, the air quality in the Sierra foothills depended on where you live. The report gave Tuolumne County a "B" grade for ozone. Calaveras County got an "A" for having particle-free air, but an "F" for smog.
The 2008 report says efforts to clean the air appeared to achieve results in cities in Southern California and the San Joaquin Valley. But it says more measures are needed to improve air quality scores in those areas.
On Wednesday, the San Joaquin Valley Air Pollution Control District board approved a cleanup plan for the tiniest soot particles, called PM 2.5. The specks are so small that they can pass through the lungs and into the bloodstream, triggering asthma attacks and heart problems.
During a lengthy public hearing, clean air activists urged the board to include tougher measures in the plan, such as restricting truck trips, farm engines and other industrial activities on bad air days.
The board rejected the proposals because of federal laws preventing the restriction of interstate commerce, said district Executive Director Seyed Sadredin.
The plan will tighten fireplace-burning regulations in the next two years, meaning no-burn days probably will triple for Northern San Joaquin Valley residents in average years.
Sadredin said he expects the tighter rules will ban residential wood burning in the Modesto area 10 to 15 days a year. The district usually imposes the wood burning bans on bad-air days from late December through February.
"What we are finding out is that during the worst particulate season, when we look at our (monitoring), about 30 percent of the pollution comes from fireplace smoke," he said.
Another measure will require employers to encourage their employees to telecommute, carpool or use alternative transportation. Employers will be given targets to meet, Sadredin said.
Diesel trucks, over which the district has little authority, are the valley's biggest source of the PM 2.5 pollution. District officials are counting on the state to adopt diesel rules to dramatically reduce the pollution.
The plan forecasts full cleanup of PM 2.5 by 2014.
The Fresno Bee contributed to this report.
Bee staff writer Ken Carlson can be reached at email@example.com or 578-2321.