Natural gas has been spewing from a ruptured well near Porter Ranch for a month, and the state Air Resources Board estimates the leak is so large that it's increasing California's atmospheric load of methane — the primary component of natural gas — by 25 percent.

Air quality officials say there is no immediate threat to human health because the methane quickly dissipates once it hits the air, but in a state whose governor has made reducing greenhouse gases a priority, it's a setback to California's environmental health.

Methane is a potent greenhouse gas that absorbs about twice as much heat as carbon dioxide.

"The leak was putting between 44,000 an 50,000 kilograms of methane into the air per hour," said California Air Resources Board spokesman Dave Clegern.

The estimate comes from samples taken by airplanes flying through the plume of methane in early November. The board also used satellites and other methods to estimate the amount of methane leaking into the atmosphere.

Caption: This chart compares the amount of methane released in California with the amount coming from a ruptured natural gas well near Porter Ranch. It's listed as "this result." Source: California Air Resources Board

The leak was first reported Oct. 23 in a natural gas field in Aliso Canyon operated by Southern California Gas Co. A 7-inch diameter well pipe surrounded by an 11-inch metal casing was leaking somewhere between the surface of the field and a few hundred feet below, spokesman Javier Mendoza said.

Initial attempts to plug the pipe by pumping brine and gravel into the well failed. Now, the company is drilling a relief well alongside at an angle to intersect the ruptured well some 8,700 feet below the surface. More brine and gravel would be put into the relief well with the goal of permanently plugging the leaking pipe. That work could take up to 90 days, Mendoza said.

Mendoza said it was too early to confirm the Air Resources Board's estimate of the methane released. The company is working on its own estimates, he said.

Methane is lighter than air and goes skyward as soon as it's released, but the chemical odorizer added to natural gas is heavier and hugs the ground. Natural gas has no odor so a "rotten egg" smell is added to aid leak detection.

The Los Angeles County Department of Public Health ordered the gas company to offer free temporary relocation to families in the area. Some 30 Porter Ranch families have been relocated after complaining of the smell, said Mendoza. The relocations are voluntary.

Paula Cracium, president of the Porter Ranch Neighborhood Council said she was still smelling the rotten-egg odor on Sunday while she worked at Shepherd of the Hills Church.

"The wind was blowing and I was at work for five hours," she said. "I got headache-y and nauseous."

The neighborhood council plans a meeting Dec. 2 that would bring together community residents and representatives of the various public agencies responding to the leak, including Los Angeles city and county officials, air quality and energy officials and some local legislators. She said they already had a location that could accommodate 300 people but were looking for a bigger venue.

Another local group, Save Porter Ranch, accused the gas company of misleading local residents about the cause of the leak and dragging its feet in offering relocation to families affected by the smell.

Mendoza responded saying the gas company has provided frequent updates about the leaks on its website and has assigned some 200 workers to try to stop the leak.

The Los Angeles City Council and county Board of Supervisors have each called on Southern California Gas Co. officials to appear before them to explain the leak and plans to correct it.

Supervisor Mike Antonovich, whose north L.A. County district includes Porter Ranch, said the South Coast Air Quality Management District would issue a notice of violation to Southern California Gas Company. Antonovich sits on the Air Quality board.

Correction: An earlier version of this story misstated the increase in emissions; it is methane emissions that are increasing by 25 percent, not California's overall greenhouse gases. The story also previously misidentified Southern California Gas Co. spokesman Javier Mendoza. KPCC regrets the errors.