Forests in Decline

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No one can say just how many trees could be saved by further emission controls. For example, it's possible that cutting sulfur dioxide emissions by, say, 20 or 30% would not reduce acid precipitation at all, because there's evidence that the relationship between sulfur dioxide in the air and low-pH rainfall isn't linear. (See the sidebar for more discussion of this point.) On the other hand, reducing emissions by 90% would be almost certain to yield an improvement.

Since the Clean Air Act was passed, sulfur dioxide emissions have leveled of and are expected to remain fairly constant through the end of the century—even without new controls. Nitrogen oxides, on the other hand, have doubled since the early 1950's and are continuing to rise. As of 1980, NO x contributed about 30% of the acid precipitation problem, but its share is expected to rise over the next 15 years.

Most current legislative proposals suggest that coal-burning utilities should further reduce sulfur dioxide emissions by about 10 to 12 million tons per year. Various experts estimate that the cost of these improvements would increase electrical rates between 4 and 15% on the average. But customers of particularly dirty utilities, such as those in the Ohio Valley, would be hardest hit.

Nitrogen oxide emissions could be reduced by about 50% through combustion modification practices . . . and at a cost of only about a 1% rate increase. Beyond that point, however, more complex techniques would be needed. Selective catalytic reductions could cut power plant emissions of NO x by 90% while causing a rate increase of 5 to 8%. Of course, though power plants are the single largest source of NO x today, they produce less than half of the total nitrogen oxide emissions in the U.S. For effective control, industry NO x emissions would also have to be controlled, and the transportation sector—despite dramatic reductions already made through the use of catalytic converters—would have to make still further improvements. (Yes, your car's catalytic converter is here to stay.)

With reductions in NO x and hydrocarbon emissions (through the use of catalysts, for example) come concomitant cuts in ozone levels, because the concentrations of the first two compounds (along with sunlight levels) affect the formation of 03. This emphasizes the importance of regulating nitrogen oxide emissions, and suggests that further improvements may have to be made on emitters of hydrocarbons, such as cars and residential heating systems.

Lead emissions from automobiles are slated for further reductions as leaded gasoline is phased out in 1986. Control of other heavy metals, however, is more problematic. Industrial processes (and particularly smelters) would need innovative controls to achieve major emission reductions.

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