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The San Joaquin Valley Air Pollution Control District calls no burn days.

The number of wood-burning curtailments in the San Joaquin Valley's eight-county air basin more that doubled this winter compared to last winter, the valley air district said in a news release Thursday.

The news should come as no surprise to anyone who experienced -- especially in December and January -- the worst winter air pollution levels in the valley's history.

During the season, which began Nov. 1 and ends Friday, the San Joaquin Valley Air Pollution Control District declared 376 curtailments -- days in all counties when wood burning was prohibited. Last winter, 186 no-burn days were declared.

Violations issued for noncompliance were also up this winter, from 384 in 2012-13 to 569 this season.

"This was an unusual winter not only for the valley but for the entire state," Jaime Holt, the air district's chief communications officer, said in the release. "Without these extreme conditions, this winter would have been the cleanest on record for the valley."

Check Before You Burn, enacted more than a decade ago, requires wood-burning curtailments on days when levels of fine-particulate matter, known as PM2.5, are forecast to exceed the federal health standard. Wood-burning forecasts are issued daily for each county.

PM2.5, microscopic soot and aerosol particles measuring 2.5 micrometers or smaller, is a particularly harmful type of air pollution that is linked to chronic lung disease, respiratory illness, heart attacks and premature death.

This year, the "historically abnormal" high-pressure system that settled over much of California was responsible for trapping particulate matter at ground level, the air district said. Many schools restrict students' physical activities when pollution levels reach dangerous levels.

The picture was the same throughout California, as even coastal areas recorded high particulate levels. For example, San Luis Obispo saw its highest PM2.5 levels on record, and other air basins experienced multiple days of exceedances and curtailments.

The valley portion of Kern County saw 51 no-burn days this winter, compared to 36 last winter.

"Despite our experience this winter, it's important for people to remember that overall we have experienced significant, long-term improvement in winter air quality, thanks to valley residents embracing Check Before You Burn and refraining from wood burning," Holt said.