Global Effects on Cities’ Smog Cited in Study

Global warming and further deterioration of the upper atmosphere’s protective ozone layer can be expected to accelerate the formation of smog in major cities throughout the United States and increase its severity in areas like Los Angeles, a new study for the U.S. Environmental Protection Agency has found.

The study is believed to mark the first time that the impact on urban air pollution of such global environmental changes has been examined and could point to new complications as the nation’s smoggiest cities struggle to clean up their air.

Depleted Ozone Shield

Based on a yearlong examination, researchers said that smog would be formed earlier in the day under conditions of global warming and a depleted upper atmospheric ozone shield. In the most polluted cities, the global effects would also increase maximum ozone concentrations.

At ground level, ozone is a toxic air pollutant that causes respiratory problems and damage to trees and crops. But at high altitudes, ozone acts as a screen to protect life on Earth from the harmful effects of ultraviolet radiation, including skin cancer and damage to crops.

Over the last several years, scientists and policy makers have become increasingly concerned about the impact of increasing global warming, known as the greenhouse effect, and the depletion of ozone in the upper atmosphere, particularly since the discovery in 1985 of a “hole” in the ozone layer above Antarctica.

There is concern that a increase in the Earth’s average temperature of up to 8 degrees Fahrenheit could precipitate partial melting of the polar ice caps and raise sea levels 10 to 12 inches, flooding low-lying coastal cities. Such climatic changes, brought on by rising levels of carbon dioxide and other so-called greenhouse gases, would also have a major impact on agriculture by shifting crop growing regions.

At the same time, sharp declines in the stratospheric ozone layer, like those observed over Antarctica, would allow more of the sun’s ultraviolet radiation to reach the Earth’s surface, increasing skin cancers, eye damage, impairing immune systems and retarding crop growth, according to the National Academy of Sciences.

But little attention has been paid to the potential impact that global environmental changes may have on air pollution.

First of Its Kind

“I think this is probably the first study that indicates that there could be an impact,” said atmospheric chemist Michael W. Gery of Systems Applications, Inc. of San Rafael, which undertook the $100,000 study for the EPA. Gery was joined by two other SAI scientists in the study, R.D. Edmond and Gary Z. Whitten. The study has been reviewed by EPA scientists and approved as an official EPA document.

The study may be controversial. Although there appears to be little disagreement that global environmental changes would have an impact on urban smog, there could be a divergence of opinion on how big the impact would be.

The study based its estimates of increased urban air pollution on far more pessimistic assumptions about the extent of global changes in the upper atmospheric ozone layer than are generally accepted.

The issue of how depleted the upper atmospheric ozone layer will be in the future is important because the ozone prevents much of the sun’s ultraviolet radiation from reaching the surface, where it drives smog production. The more ultraviolet radiation, the more urban smog. Smog is formed when hydrocarbons and oxides of nitrogen react in the presence of sunlight. Examples of hydrocarbons would be gasoline or paint vapors. Oxides of nitrogen are the products of burning fossil fuel and are emitted from such sources as vehicle tailpipes and oil refinery stacks.

The SAI study assumed in its “moderate” case that the upper atmospheric ozone shield will be thinned by 16.7% sometime between the years 2010 and 2030. However, other scientists have said they did not expect more than a 10% decrease before the middle of the next century. More recently, even that estimate has been revised downward after 47 nations in September signed a treaty in Montreal limiting the production of ozone-depleting chlorofluorocarbons (CFCs), which are used as refrigerants, propellant for aerosol spray cans and in the manufacturer of foam products. Under the agreement, production would be held at 1986 levels until Jan. 1, 1990, and then reduced by 50% by 1999.

Doubts on Severity

In Washington, EPA spokesman Chris Rice said the study was undertaken at a time when it was assumed that the use of CFCs would continue to grow annually. But, he said, in view of the Montreal protocol the depletion of the ozone layer is expected to be far less severe that the study assumed.

But Gery said he was comfortable in basing his moderate case scenario on a 16.7% depletion of the ozone layer. He said no one knows how beneficial the treaty may be. In the nation’s smoggiest cities, air pollution increases could range from 23% to 45%, depending upon how high world temperatures rise and, more important, how thin the upper atmosphere’s ozone layer becomes, the report said.

But Rice said, “If you look at the scenarios of decreasing stratospheric ozone of 3% to 5%, which is much more probable over the next 75 years, the differences in urban ozone are in the neighborhood of 2% to 5%.”

Meteorological and air pollution data were gathered for the SAI study from representative cities for specific days. Assuming a 16.7% decrease in the protective upper atmosphere ozone shield and a two degree centigrade (3.6 degrees Fahrenheit) increase in temperature, air pollution in the Los Angeles basin on the day studied would increase by 15.2%. If global warming went up five degrees centigrade and the ozone layer was reduced by 33%, air pollution would jump nearly 50%.

Similar increases were postulated for other cities for specific days studied. They were 25.6% in New York, 23.7% in Philadelphia, 26.1% in Washington, 10% in Phoenix and 1.6% in Tulsa.

Concern Over Compliance

In each case, the global environmental effects would have thrown those cities out of compliance with federal clean air standards if they otherwise had been in compliance.

For millions of residents in the most populated coastal and central areas of the South Coast Air Basin, the formation of smog earlier in the day would mean that they may no longer escape air pollution episodes that often have been restricted to eastern areas of the basin such as Pasadena, Fontana and Riverside, Whitten said in an interview.

“With increases in ultraviolet radiation we’d expect smog to form earlier in the day and be with us a long time. The smog would form closer to the emission sources where more people are. More people would be exposed to higher levels. In some cities the sun sets before smog has a chance to get worse. Those cities would get worse,’ Whitten explained. The worldwide environmental changes could seriously hamper plans to bring the four-county South Coast Air Basin into compliance with national clean air standards within 20 years. “We’re liable to have to double that in terms of the global effect,” Whitten said. The basin includes the counties of Los Angeles, Orange, Riverside and San Bernardino.

“It’s a frustrating situation,” Whitten said. “We’ve had air pollution controls in our cities and autos for a couple of decades and we still have a smog problem. This seems to indicate that it’s going to be even harder in the future to keep the smog levels down.”

“Assuming all other factors are equal, areas with additional radiant energy input would most likely be required to implement more hydrocarbon emission controls to attain the same air quality,” the report said.

James M. Lents, executive officer of the South Coast Air Quality Management District, said the study’s findings would be “disheartening” if they turn out to be true.

“Hopefully we’ll solve this CFC problem and not have to face that issue,” he said.