Valley air officials this month asked federal authorities to ignore a massive pollution spike caused this year by Fourth of July fireworks.
Readings in Bakersfield jumped more than six times above the health threshold, said the San Joaquin Valley Air Pollution Control District. The agency is invoking a federal rule on events out of its control -- a rule available to air districts across the country.
The U.S. Environmental Protection Agency is expected to exclude the readings. The last day for public comment on the district's request is Jan. 11.
If the high readings were included in the Valley's monitoring information, the district might have violated the coarse-particle standard for dust, soot and chemical specks. The Valley has achieved clean-air status for the so-called PM-10 standard with no violations since 2003.
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A July 4 violation would move the region back out of the clean-air status. Officials would have to look at new and possibly expensive particle-pollution controls, such as spreading oil on more unpaved roads to hold down dust.
Environmentalists say the July 4 exception appears to be within federal rules, but they said the EPA should not look for more reasons to excuse potential air violations.
The EPA last year disregarded three particle-pollution violations due to high wind that kicked up dust and caused high readings. The agency excludes such readings if the air district can prove there would not have been a violation without the wind.
"How many other types of events will be used?" asked Sarah Jackson, research analyst for Earthjustice, a nonprofit legal watchdog in Oakland.
On July 4 in Bakersfield, high particle readings occurred between 9 and 11 p.m. The readings followed fireworks displays that showered the sky with smoke and metals, such as magnesium, copper and barium.
Such metals can cause health effects ranging from skin irritation to muscle weakness and confusion in people with kidney problems. But air officials say the particles, known as PM-10 and PM-2.5, clear in a matter of hours.
Before the fireworks shows, a Bakersfield PM-10 monitor recorded a healthy 48 micrograms of particle pollution per cubic meter of air. A 150 average over an entire day is the health threshold.
But at 8 p.m., the reading vaulted to 471. An hour later, it was pegged at 943.
By 1 a.m., the monitor dropped to 138 micrograms, meaning it was back in the healthy range.
Valley air officials say the numbers provide evidence that there would have been no particle increase if not for fireworks. Air officials said they do not have authority over Fourth of July fireworks shows.
Said district meteorologist Gary Arcemont: "It's an event that is clearly out of our control."