As of the completion of the first report to Congress, several observations have been made regarding the success of Title IV It appears that the market-based approach has lowered compliance costs. Costs are lower than expected, probably due to a number of factors such as railroad deregulation, technological innovation, and lower operating costs for scrubbers. In addition, all affected utilities have fulfilled the compliance requirements of Title IV In the first annual reconciliation of allowances and emissions, S02 allowances matched or exceeded S02 emissions. NOr reductions have not been as dramatic. This is expected since mandates on NOr reductions are not in place yet. However, NOr emissions from all sources in 1995 were 1.5 million tons below 1980 levels. Utilities were responsible for 53% of that reduction.
Statistically significant reductions in acidity and sulfate in precipitation were reported at monitoring sites in the Midwest, mid-Atlantic, and northeastern United States. There is no real evidence of statistically significant decreases in nitrate concentration. Changes in aquatic ecosystems have not yet been detected. However, over the last 15 years, lakes and streams throughout many areas of the United States have experienced decreases in sulfate concentration in response to decreased emissions. While there is some evidence of recovery from acidification in New England, Adirondack lakes continue to acidify, suggesting that additional reductions may be needed in these areas (NAPAP, 1998).
Sulfur and nitrogen deposition has caused adverse impacts on certain sensitive forest ecosystems in the United States, with high-elevation spruce in the eastern United States being most sensitive. Other sensitive forests are apparently not experiencing the same effects in mortality and growth, at least for now, but some of the same processes appear to be slowly occurring.
The leaching of soil nutrients by continued acidic deposition is a gradual process that will eventually impact forest nutrition and growth in many areas. The recent reductions in sulfur should result in some small immediate improvements in sensitive forests, but large improvements will be slow to occur.
Reduced emissions of sulfur oxides are expected to reduce sulfate concentration and its contribution to haze. It is difficult to assess the extent to which recent reductions have contributed to changes in visibility over the past few years since meteorological and other factors determine the overall changes in visibility. Information is needed over the long term.
The recent reductions in SOx and NOr emissions are expected to reduce fine particulates and, as a result, lead to improved human health. It is suggested that reduced emissions will lead to a reduction in premature mortality from cardiovascular and respiratory causes and to a dramatic reduction in the number of asthma symptom days.
One difficulty in determining effects at this time is that many impacts have a response times that are longer than the few years since the passage of Title IV Visibility and acute health effects can be detected on the order of hours to days. Episodic aquatic effects and soil and plant processes in the forest ecosystem respond on the order of days and weeks to months. Chronic human health, chronic aquatic effects, and forest health, on the other hand, indicate response times on the order of years to decades. Effects on forest solid nutrient reserves and effects on materials begin to show up on the order of decades to centuries. These latter effects are more on the order of climate change impacts response times.
The difference in response times, of course, makes an evaluation of actions taken in the early 1990s difficult to quantify. Improvements in health and visibility can serve as indicators of positive change. However, as already noted, even changes in visibility cannot be directly attributed to sulfate reductions alone, since other factors such as meteorological variability play a role in determining visibility changes especially in the humid part of the eastern United States.
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