WASHINGTON — California cities, including Merced, Modesto and Fresno, continue to have some of the worst air in the United States, according to the American Lung Association's "State of the Air 2013" report.
The annual report, which tracks air pollution across the country, ranked Bakersfield as the sootiest city in the country, followed by Merced and Fresno. Modesto was No. 6. Many California cities also ranked high in ozone pollution, particularly in the summer.
Air pollution remains a pervasive public health threat across the United States, said Harold Wimmer, national president and chief executive officer of the American Lung Association.
More than 131.8 million Americans, about 42 percent of the population, live in counties that have unhealthy levels of ozone or particle pollution, the report found.
However, Jaime Holt, chief communications officer for the San Joaquin Valley Air Pollution Control District, said ranking Merced at the top of the list for particle pollution isn't accurate and was based on partial data.
"Merced is not the worst offender," she said, adding that the monitor from which the data were taken was operational for only part of the year -- in the winter when the worst particulate matter is recorded. It didn't include months with cleaner air.
"It was just a small snapshot of the year," Holt said.
She said she thought the American Lung Association should have included an explanation in its report.
The air quality isn't the best in the Merced area, Holt said, but it's far better than what was presented in the American Lung Association's report.
"We don't have pristine air quality -- we understand that," she said. "It's a really complex issue here in the valley."
Most of the particle pollution comes from cars, diesel trucks and residential wood burning.
Holt said businesses and industry have invested about $40 billion toward cleaning up the air. That investment has led to an 80 percent reduction in pollution from those sources over the past 20 years.
Merced Mayor Stan Thurston said much of the local pollution blows in from the Bay Area and settles in the valley because of its bowl shape.
Local leaders encourage healthy living that promotes a cleaner environment, such as riding bicycles, but major improvements in air quality often come from advancements in some of the more notorious polluters, Thurston said.
Diesel trucks and farm equipment have gotten more efficient through the years, resulting in less pollution, he noted.
The American Lung Association's report also shows that air quality nationwide continues in a long-term trend toward much healthier air.
"Even in parts of the country that experienced increases in unhealthy days of high ozone and short-term particle pollution, they still have better air quality compared to a decade ago," Wimmer said in a statement.
The report found that compared with last year, many places made strong progress in lower year-round levels of particle pollution.
The report suggests that's a direct result of transitioning to cleaner diesel fuels and engines and reduced emissions from coal-fired power plants, especially in the eastern United States.
The association will urge the Obama administration to take action in the next year, including establishing standards to reduce tailpipe and smokestack pollution.
The American Lung Association report came out the same day the California Environmental Protection Agency released the nation's first comprehensive statewide environmental health screening tool.
Known as CalEnviroScreen 1.0, the tool allows people to see how much pollution they have in their communities and who is most vulnerable to its effects.
The tool uses data from about 11 types of pollution and environmental factors and seven population characteristics and socioeconomic factors to create scores for each ZIP code in California.
The agency says it will help state decision-makers figure out which communities need target grants, investments, cleanup efforts and enforcement actions, particularly in the state's most disadvantaged communities.