San Diego County air pollution regulators are battling California officials over the state’s contention that imported liquefied natural gas (LNG) potentially is raising pollution levels, and they want San Diego Gas and Electric Co. (SDG&E) to do something about it. SDG&E contends that there is no problem and it can’t stop the flow of gas imports anyway.

The San Diego County Air Pollution Control District is particularly concerned about the California Air Resources Board (CARB) allowing these gas supplies to be used in transportation for buses and fleet vehicles using compressed natural gas (CNG).

The debate centers on supplies from Sempra Energy’s LNG terminal along the Pacific Coast of North Baja California, Mexico, at Energia Costa Azul. It is those supplies of “hotter,” higher-Btu gas that the air district officials allege are raising the pollutants released when the gas is burned or used in transportation.

While contending that the county air district has flawed information, SDG&E officials stressed that the Sempra utility is working with the California Energy Commission, CARB, the Lawrence Berkeley National Labs, the Gas Technology Institute and others, including the county pollution district, to address what it contends are “information gaps” in assessing whether pollution levels have been raised under the current standards for gas supplies (domestic and imports) coming into California.

“The district agrees that more research is required,” said Bob Kard, head of the San Diego pollution district, as part of an interview published by the San Diego Union-Tribune. “However, the district estimates of potential emissions are based on the best information available and are sufficiently accurate to identify a potential air quality impact from the use of LNG-derived natural gas in place of our historic domestic supplies.”

SDG&E officials contend that the source of the gas is not relevant; it is the quality as set by state standards that is the issue. “In 2006 the California Public Utilities Commission [CPUC] approved gas quality specifications that were more stringent than they had been, and all interstate and LNG sources of natural gas must meet these requirements,” said SDG&E spokesperson Art Larson, as part of the Union-Tribune interview.

Pollution regulators have reiterated their support for natural gas-powered transportation, but not if the gas comes from what they consider to be more polluting LNG-derived supplies. Larson called the CARB exemption for using the gas in CNG transportation operations “a holding action” to ensure that there are no disruptions to clean transportation fleet operations, primarily local transit buses.

Last year about 118 Bcf of natural gas was delivered to San Diego County, 4.3% from LNG-derived supplies that come through SDG&E’s Otay Mesa receipt point south of San Diego near the Mexican border. LNG-derived gas supplies have been coming into San Diego County since 2008, and the first shipments were tested by the San Diego County air district, Larson said. Those test results were uncertified, however.

SDG&E’s natural gas system can handle a maximum peak load of about 630 MMBtu/d, and on Jan. 4 its demand was 440 MMBtu/d. A cross border pipeline from North Baja has a maximum capacity of 400 MMBtu/d. The LNG is be “richer,” or higher in its heat content, and thus, is dubbed “hot” gas.

“Btu content of some sources of natural gas brought into the state via interstate pipelines from the Rockies, Texas and Canada and many of California’s native gas supplies is the same as that of LNG-sourced natural gas,” Larson said.

While the quality and composition of gas supplies can vary from one region of the United States to another, it can also vary between different areas of the world. The industry has a heat density measure used to determine the interchangeability of supplies, called the Wobbe Index. In California the CPUC-established Wobbe standard is 1,385, and this compares to Indonesian gas supplies that come into Sempra’s North Baja terminal that have a Wobbe of 1,372, well within the California limit.

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