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AQMD's Smog Predictions: How Clear Is the Vision?

Environment: Critics say agency's new computer modeling is too optimistic.


Fast forward to an August afternoon in Los Angeles, a decade into the 21st century. Do the skyline and mountains sparkle in a sea of blue, or is the region still cloaked by a filthy, lung-stinging layer of smog?

The ability of the South Coast Air Quality Management District to accurately predict the future has become a focal point in the controversy over a new plan that will guide Southern California's effort to combat pollution.

The AQMD's latest clean-air plan relies upon computer-generated scenarios of what smog will be like in the year 2010 that entail as much speculation as fact. The scenarios have triggered the suspicions of scientists, environmentalists and other critics because the AQMD switched to much rosier predictions without having its methods scrutinized by independent experts or its own advisory council.

The new forecast is such a dramatic departure from predictions made in a 1994 plan that some critics are questioning whether the AQMD engineered its computer modeling in order to appease politicians and businesses that want smog rules eased. Because the new models found that fewer emissions must be eliminated to achieve healthful air, future clean-air remedies can be less painful and less expensive.

"Because I'm a modeler, I know how uncertain the exercise is," said Akula Venkatram, a UC Riverside engineer who was one of nine members of the AQMD's scientific advisory council who resigned Aug. 8 in protest. "In science, one assumes the modeling practices are bad unless there is proof they are good."

The computer modeling is the compass navigating the tortuous path toward cleaner air. It directs the range and scope of all future smog rules in Los Angeles, Orange, Riverside and San Bernardino counties, an area of 13 million people. The AQMD's new, more optimistic predictions could save businesses millions of dollars annually in an anti-smog bill estimated in 1994 to exceed $5 billion per year.

The Environmental Protection Agency and the state are reviewing the new computer modeling to see if it was technically sound, but AQMD executives say their analytical team is sheltered from the political fray and followed the latest, scientifically sound practices.

"There has been political pressure, but that did not influence any decisions on the modeling," said AQMD Executive Officer James Lents. "We stand by the work."

After a series of public workshops to detail the plan's methods beginning next week, the agency's governing board expects to vote on the new air quality plan--based on the more optimistic computer models--on Nov. 8.

In predicting smog into the 21st century, the AQMD has factored in hundreds of assumptions about the future--from the miles driven by cars to the wind flow on summer days, the reactivity of various chemicals and the volume of manure excreted by dairy cows.

The modeling process is so complex that only a handful of people outside the agency understand it. Yet if a single factor is off, it can skew the entire outcome, forecasting skies that are cleaner or dirtier than reality and yielding an attack on smog too weak or too vigorous.

In their resignation letter, the AQMD's advisors from USC, UCLA and other institutions said the agency "is embarked on a course that will not lead to attainment" of federal health standards. They cited as a major reason the "large uncertainties in the models, data and assumptions used to predict air quality" and a lack of external review.

"The model they are relying on is extremely sensitive to changes in information, and there is a lack of confidence about their predictions," said Jane Hall, a Cal State Fullerton economist who quit the advisory council.

"Various members of the council have worked with staff and have not been able to effect change as far as how the databases were assembled," she said. "The district is not looking for external advise."

Mel Zeldin and Henry Hogo, the AQMD managers who led the analysis, said they reached the more optimistic predictions after a two-year, $1.4-million overhaul of the data plugged into the model. The study provided more reliable and updated estimates of the volumes and sources of particulate pollution, especially in Riverside and San Bernardino counties, they said.

"The 1994 data was a crude approximation at best," said Zeldin, project manager for the clean air plan. "We have a much better way now of simulating it."

The AQMD has been renowned for its technical expertise, and the analysts for the plan collectively have 200 years experience in modeling air quality, said AQMD deputy executive officer Barry Wallerstein. The models were checked for accuracy by seeing how well they would have predicted past years' smog, and they performed well, Zeldin said.

Still, the AQMD analysts concede that some assumptions they plugged in are arguable, and that approximating such a complex chemical and meteorological process 14 years into the future is precarious. The plan is scheduled to be revised again in 2000.

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