Local authorities and environmentalists are protesting construction of a $1 billion natural gas terminal in Mexico about 50 miles south of the U.S. border.

The Sempra Energy terminal, now in the final phases of construction, will receive liquefied natural gas from overseas via tanker, and inject it into existing natural gas pipelines, The San Diego Union-Tribune reported Sunday.

But the gas that will be processed at the new terminal contains higher levels of chemicals that produce nitrous oxide, which contributes to ozone pollution, the newspaper said. Once the gas is imported to the United States, it could considerably worsen air quality in Southern California.

The technology to make the gas cleaner exists, the Union-Tribune said, but regulator are not requiring it be used, and Sempra does not want to assume the additional cost.

Sempra has said the connection between gas that has not been cleaned and higher levels of air pollution has not been scientifically proven.

Copyright 2007 by United Press International