Testing of air samples from locations in the Inland Empire and around the Salton Sea appear to have revealed the cause of a sulfur odor that fouled the air in areas of Southern California Monday.
As suspected, the culprit was likely the Salton Sea, a large saltwater lake about 150 miles east of Los Angeles that often has decaying fish and algae on its shores.
The South Coast Air Quality Management District said it had taken samples from 10 locations in the Inland Empire, Coachella Valley and near the Salton Sea. The samples showed a progression of hydrogen sulfide levels that were strongest near the sea.
"We now have solid evidence that clearly points to the Salton Sea as the source of a very large and unusual odor event," said Barry Wallerstein, executive director of the district, which oversees air quality in much of Southern California.
AQMD had suspected the 376-square-mile body of water as the source of the smell, but air district officials said late Monday that more investigation was needed to be certain about the cause of the rotten-egg odor.
Inspectors were in the field Monday in the San Fernando Valley, Long Beach, Colton, San Bernardino, Riverside, Perris, Temecula, Banning, Palm Springs, La Quinta and the Salton Sea, the agency said.
They found decreasing concentrations of hydrogen sulfide as distance grew from the Salton Sea.
The chemical compound, which is a product of organic decay such as that which occurs at the sea, has an "unmistakable rotten-egg odor," according to a press release issued by AQMD Tuesday evening.
The Salton Sea has regular massive fish kills in its waters, which are often polluted with pesticide runoff from nearby agricultural operations.
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The agency said it ruled out other potential sources of the smell such as landfills and oil refineries. An examination of recent weather patterns showed the smelly air could have traveled such a long distances, the air district said.
AQMD had received about 235 complaints about the odor Monday, and just about a dozen overnight and Tuesday morning. The strong stench, however, could be easily detected in some parts of central Los Angeles late Tuesday night.
Thunderstorms around the Salton Sea and high winds could have stirred up bacteria-laden water from the bottom of the sea, pushing the odor more than 100 miles to the Los Angeles region, the air district said.
"Winds from the southeast of at least 50 mph pushed odors from the Salton Sea to the northwest – across the Coachella Valley, through the Banning Pass and across the Los Angeles Basin," the AQMD said in a statement.
An onshore breeze from the west has since kept odors at bay.
Late Monday, Wallerstein said it was "highly unusual for odors to remain strong up to 150 miles from their source."
The agency said the high concentrations of hydrogen sulfide were not enough to cause "irreversible harm to human health."
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