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Axel Koester/The New York Times

Susan James, 50, of Bakersfield, using her inhaler at Beach Park near Interstate 99 in Bakersfield, June 29, 2007. James says she has developed lung problems from years of running in polluted air.

The San Joaquin Valley Air Pollution Control District has always had a difficult story to tell.

Each year district officials assert that significant progress has been made in improving the valley's air quality. And each year, Bakersfield is listed among cities with the worst air in the nation.

It's a dichotomy that is not immediately apparent in the air district's annual "Report to the Community" released Tuesday.

The report documents the eight-county district's successes and acknowledges the "challenges" the valley continues to face in controlling particulate pollution -- a winter malady -- and ozone pollution, or smog, the scourge of the hot summers.

"The progress we've made together over the past two decades is unmistakable," wrote Seyed Sadredin, the district's executive director. He cited an 80 percent reduction in air pollution from businesses and "the cleanest winters and summers on record" as victories that should be celebrated.

The district, which extends from San Joaquin County in the north to Kern County in the south, has charted significant reductions in the number of days with unhealthy air quality, and is "closer than ever to meeting tough new health standards for ozone," Sadredin said.

But critics see things differently.

"We still have the worst air in the country," said Gordon Nipp, a longtime volunteer with the Sierra Club. "One in six children in the valley has asthma. This is a major public health issue."

Nipp said there have been improvements in air quality but most gains have come from "low-hanging fruit," such as pollution controls on refineries.

"Business needs to kick in," he said of efforts to reduce pollution, "not just poor people who pay an additional vehicle license fee."

But Sadredin says valley businesses have invested billions in reducing air pollution since 1992, when the district was formed.

According to the report:

Limitations placed on wood-burning fireplaces have been both cost-effective and health-protective. Look for directives in 2014 that will tighten the rules even further.

Legislative action is needed to update the federal Clean Air Act, in part because it creates "standards and deadlines that are impossible to meet" and enormous costs to state and local governments, businesses and individuals "without any corresponding benefit to air quality."

Since 1992, the district has provided nearly $500 million in incentives for strategies to voluntarily reduce emissions. These efforts have resulted in a reduction of more than 98,000 tons of harmful emissions.