Acid Fog Could Peril San Joaquin Valley, Study Says

Acid fog could envelop the southern San Joaquin Valley, one of the nation’s major farm areas if ammonia from cow manure becomes inadequate to neutralize acid from oil industry pollutants, a study says.

“At present, there is a close balance between emissions of ammonia and acidic compounds in the valley during air stagnation episodes,” said Daniel Jacob, a Harvard University atmospheric chemist and main author of the study financed by California’s Air Resources Board.

“Alteration of this balance could lead to a serious, widespread acid fog problem in the southern end of the San Joaquin Valley” during winter air inversion periods, said Jacob, who conducted the study for his doctoral thesis at Caltech.

Acid fog can be up to 100 times stronger than acid rain and more than 10 times stronger than vinegar, experts say. Acid fog, rain and dry acid fallout are created when nitrogen oxide and sulfur dioxide pollutants from fossil-fuel combustion undergo chemical reactions in the air to form nitric and sulfuric acids.

In the southern San Joaquin--the Kern County portion of the valley--acid-forming pollutants are produced largely by oil-burning steam boilers used to inject steam underground to ease crude oil extraction, Jacob said, adding that the exhaust from cars, trucks and farm equipment also contributes.

Acid fog can be neutralized by ammonia gas. About 60% of the ammonia in southern valley air comes from cow manure, while about 30% is emitted by fertilizers and soil bacteria, Jacob’s study estimated.

The study, published recently in the Journal of Geophysical Research, found that fog on the western edge of Kern County near McKittrick was consistently acidic when winter air inversions trap pollutants and foster formation of dense fog known locally as “tule fog.” The fog averaged about 10 times weaker than vinegar, but occasionally was stronger than vinegar.

“On the east side (of the valley near Bakersfield), we usually did not have acid fog because there was enough ammonia to neutralize the acid,” Jacob said. “If the ammonia emissions decrease a little bit so there wouldn’t be enough ammonia to decrease the acid, then right away you would have a serious acid fog problem.”

That has already happened on rare occasions when the study found that fog near Bakersfield was more acidic than near McKittrick, he added.

Acid fog is a known lung irritant, but no one knows exactly how harmful it is to human health, crops or buildings. The Air Resources Board is sponsoring a four-year, $18-million research program to find answers, spokesman Bill Sessa said.

Strong acid was present in the so-called “killer fog” that shrouded London in 1952 and was blamed for about 4,000 more pollution-related deaths than might have been expected.

The San Joaquin’s acid fog “certainly isn’t any sort of London fog,” said William Munger, a Caltech researcher and study co-author. “But people who are sensitive, who have asthma, may find acids in fog may aggravate the (lung) conditions they have.”

In recent years, the Caltech research group has found acid fog in coastal areas of Los Angeles, Orange and San Diego counties, mountain slopes above Santa Barbara and in Riverside and San Francisco, Munger said.

People with lung ailments should stay indoors and avoid strenuous exercise during foggy periods, said Stan Dawson, chief of the Air Resources Board’s biological effects branch.

Greenhouse studies have shown that crops can tolerate a lot of acidity. But acid fog in the southern San Joaquin Valley has been measured at levels strong enough to injure plant leaves, which reduces the value of leafy crops, said Robert Musselman, a plant physiologist at UC Riverside.

Some farm experts say it’s possible that acid fog, rain and dry fallout may benefit San Joaquin farmers, since some soils there are too alkaline for crops and now are treated with acids.

California’s Department of Food and Agriculture ranked Kern County as the state’s third-largest county in terms of agricultural production in 1984. The 1982 federal farm census, the latest available, ranked Kern third in farm output among all counties nationally. Kern’s major crops include cotton, grapes, almonds, carrots, alfalfa and potatoes.

Pollutants Reduced

Pollutants that spur acid fog in the valley have been reduced in recent years because of greater use of natural gas for the oil industry’s steam generators, and because of more stringent government pollution rules, said Stephen Ziman, a senior environmental engineer for Chevron U.S.A.

However, the recent sharp fall in oil prices means that for the short term, oil companies are more likely to use oil than natural gas to power the generators, said Bill Brommelsiek, a Chevron environmental manager.

The oil-price drop recently prompted oil companies to take numerous wells out of production. But few pollution-emitting steam generators will be turned off because oil companies want to maintain the underground heat that makes it easier to extract oil, he said.

Sharp Drops Predicted

K. C. Bishop, an environmental coordinator for Chevron, said a recent study by a San Rafael consulting firm predicted sharp drops from 1980 to 1995 in pollutants that form acids in the valley’s air.

Jacob agreed that acid-forming pollutants are likely to diminish in the future but he said a sharp drop in the number of cattle in the valley in recent years probably is reducing the ammonia available to neutralize acid fog.

Any increase in population and traffic in the valley also could lead to more acid fog, Caltech’s Munger said.