RICHMOND (CBS SF) — In the Bay Area, residents are constantly reminded to ‘spare the air’, but air quality managers may be letting some of the worst polluters off the hook.

Chevron runs the Bay Area’s biggest, and busiest oil refinery, and they are mandated to keep careful tabs on air emissions.

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“We’ve been working since the 1970’s to reduce emissions, and we have reduced them by over 87 percent,” Nicole Barber of Chevron said.

But, deep in a 2,000-plus page environmental impact report for Chevron’s proposed modernization project, there’s an emissions inventory that shows test results from the refinery’s main gasoline making unit in 2009.  That test revealed that the unit was releasing 343-tons in emissions per year, more than three times higher than the permit limit of 92.

“The monitoring shows that they are emitting this stuff,” Greg Karras of Communities for a better Environment said.

Karras says the numbers are higher because they include the finest particulates coming out of the stack, which are 20-times smaller than a strand of hair called PM 2.5. Most of these particulates can only be detected using a condensing device, something Chevron doesn’t use.

“This is really a killer pollutant, they are letting it continue, and they have for five years now,” Karras said.

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But, the practice is perfectly legal, because the air district doesn’t place a limit on what are called condensable PM’s, even though some experts say those fine particles are the most dangerous part of air pollution.

“It can make its way down to the air sacks of the lungs, where it can lead to inflammation,” UCSF Doctor John Balmes said.

But, the method used to test Chevron’s unit is no longer valid, according to the air quality district.

“The belief is that they over-estimate the condensable portion of particulate matter,” Bay Area Air Quality Management District staff member Eric Stevenson said.

Chevron says their hands are tied.

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“Because there is no endorsed or accurate methodology for monitoring for fine PM, there isn’t anything we can do at this time,” Barber said.