SAN DIEGO -- The Palomar Energy power plant in Escondido got a one-year break on emission rules from air pollution regulators Thursday for the times that its two gas-fueled turbines are firing up.

However, plant operator San Diego Gas & Electric Co. agreed to a restriction it said would limit its per-hour production of smog-generating chemicals: Only one turbine can start up at a time.

The San Diego Air Pollution Control District's hearing board also asked that the utility study installing additional pollution control technology and report back every three months on its progress.

Ray Kelly, a compliance manager from SDG&E's corporate cousin Sempra Global, said the power plant's operators had asked for "reasonable changes" that would allow the plant, which started full commercial operations a month ago, to keep running.

The variance granted by the board Thursday allows Palomar to produce 225 pounds of nitrogen oxides per turbine per hour during start-up time, rather than the originally permitted limit of 100 pounds per turbine per hour.

The variance also allows extra start-up time: three hours instead of two if the plant has been inactive for less than 48 hours, and six if the plant has been inactive for more than 48 hours.

The plant uses a catalytic converter -- like a car's, but much larger -- to reduce the amount of nitrogen oxides in its exhaust. However, that process doesn't work well when the turbines are cold, according to Dan Baerman, the plant's director of electricity generation.

When one of the turbines is already hot, the other turbine's start-up should be cleaner than both at once, he told district officials at the meeting.

During steady operation, the turbines are allowed to generate 13.4 pounds of nitrogen oxides each, district compliance manager Heidi Gabriel-Pack said. The air pollution district did not change those limits.

Kelly said Palomar has been running continuously for the last month but one turbine is shut down at night. The plant's daily operations are controlled by the Independent System Operator, the manager of the state power grid.

Nitrogen oxides are byproducts of burning both natural gas to drive steam turbines and burning gasoline in car engines. They form ozone, the main lung irritant in smog, in the presence of sunlight.

Cars and trucks are by far the largest sources of nitrogen oxides in San Diego County, producing more than 170 tons a day. Palomar has permission from the California Energy Commission to make a total of 124 tons of nitrogen oxides per year.

SDG&E officials said that limit would not be broken as a result of the variance.

Palomar operators have already sought six shorter variances in the last year as they were testing the plant, starting last October.

At the meeting, Ruth V. Rodriguez, vice chairwoman of the hearing board, gently chided Sempra and SDG&E officials for delays in reporting some of the emissions data.

"By the seventh (variance request), we should have our act together," she said.

Rodriguez said Sempra should have anticipated that Palomar would require longer start-up times because it has experience with similar power plants such as the Elk Hills Energy Project in Kern County.

Most modern "combined-cycle" power plants such as Palomar and Elk Hills, which use both gas-fueled and steam-driven turbines, take more than two hours to start up, according to California Energy Commission records.

Contact staff writer Quinn Eastman at (760) 740-5412 or qeastman@nctimes.com.