نگاه تازه در سود و زیان برنامه باران اسیدی آمریکا

The US Acid Rain Program (Title IV of the 1990 Clean Air Act Amendments) has achieved substantial reductions in emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx) from power plants in the United States. We compare new estimates of the benefits and costs of Title IV to those made in 1990. Important changes in our understanding of and ability to quantify the benefits of Title IV have occurred. Benefits to human health now take a much higher profile because the contribution of SO2 and NOx emissions to the formation of fine particulate (PM2.5) is substantial, and evidence of the harmful human health effects of PM2.5 has emerged in the last 15 years. New estimates of the health benefits of PM2.5 reductions are the largest category of quantified health and environmental benefits and total over US$100 billion annually for 2010 when the program is expected to be fully implemented. Although important uncertainties exist in any specific estimate of the benefits, even if the estimates were calculated using more limiting assumptions and interpretations of the literature they would still substantially exceed the costs. Estimates of annualized costs for 2010 are about US$3 billion, which is less than half of what was estimated in 1990. Research since 1990 also suggests that environmental problems associated with acid deposition and nitrogen deposition are more challenging to resolve than originally thought and will require larger reductions in emissions to reverse. The greater than expected benefits to human health, the greater vulnerability of natural resources and ecosystems, and the lower than expected costs all point to the conclusion that further reductions in SO2 and NOx emissions from power plants beyond those currently required by Title IV are warranted.

Title IV of the 1990 Clean Air Act Amendments (CAAA), also known as the Acid Rain Program, has achieved substantial reductions in US electric power industry emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx) at lower costs than originally predicted. New estimates of the human health and environmental benefits of Title IV are calculated and contrasted with the US Environmental Protection Agency's (US EPA's) most recent estimates of the costs of Title IV. The benefits are estimated using the US EPA's most recent projections of emissions of SO2 and NOx from power plants in 2010, after Title IV is fully implemented, in comparison to projections of what emissions would have been in 2010 without the Title IV regulations. Congress passed Title IV of the 1990 CAAA to reduce emissions of SO2 and NOx from fossil fuel-fired power plants. The SO2 program is a departure from previous regulatory approaches because it sets an overall emissions cap and allows trading of emissions allowances between facilities, thereby creating flexibility for the regulated entities to find the lowest cost approach to reducing total emissions. The permanent cap on total annual SO2 emissions to be reached in 2010 is 8.95 million tons, which is about half the amount emitted by power plants in 1980. The Title IV NOx provisions are emission rate limits based on available control technologies. NOx emissions from power plants are also being reduced by Title I, under which the National Ambient Air Quality Standards (NAAQS) are implemented. Since proposals to reduce power plant emissions beyond the Title IV requirements are under consideration by the Administration and by Congress, it is timely to reassess what Title IV has accomplished.

One of the most important uncertainties in the 1990 assessment concerned what emissions would have been by 2010 in the absence of the program. Some projections showed that other requirements of the Clean Air Act (primarily NSR) would have resulted in power plant emissions reductions as large as those required by Title IV by 2010 or soon thereafter. This might have happened if existing power plants gradually retired older equipment and installed new emissions control equipment, but the upgrading or retirement of the older power plants has been slower than the 1990 predictions. Thus US EPA's current estimates are that without Title IV, emissions through 2010 would have increased slightly from 1990 levels. Table 5 summarizes Title IV costs and benefits. Important changes in our understanding of and ability to quantify the benefits of Title IV have occurred since the 1990 assessment. Benefits to human health now take a much higher profile because the contribution of SO2 and NOx emissions to the formation of PM2.5 is substantial, and evidence of the harmful human health effects of PM2.5 has emerged in the last 15 years. The central estimates of quantified benefits exceed costs by two orders of magnitude. Although important uncertainties exist in any specific estimate of the benefits, even if the estimates were calculated using more limiting assumptions and interpretations of the literature they still would substantially exceed the costs.