付録5
MTBE関連資料
* Oxygenerated Fuel Program and Reformulated Gasoline Program Transportation Statistics Annual Perort 1997抜粋 DOT
* MTBE: Concern or Crisis for U.S. Drinking Water Ark Institute
* Boating and MTBE NMMA
* Shore Residents sue over MTBE Pollution Star Ledger, Aug. 25, 2000
reused. Those that cannot be reused are sold as landscape materials, parking bumpers, fence posts, and retaining walls, or sold to power-plants. Only the worst ties are placed in landfills. Like wooden ties, treated timber from bridges and other structures are either reused or disposed of. Used concrete ties and most plastic rail-tie components are placed in landfills. Fine materials removed from cleaning ballasts are occasionally reused on roads. (TRB 1996, 28-31)
New Strategies for Reducing Air Pollution
Increasingly stringent emissions standards for light-duty highway vehicles have been instrumental in reducing transportation-related air pollutants. Several efforts to reduce emissions further have been or will soon be implemented. Discussed here are four that resulted from the CAAA:
■ oxygenated fuels and reformulated gasoline programs in areas with persistent air quality problems;
■ new emissions standards for heavy-duty high-way and nonhighway vehicles;
■ revised Federal Test Procedures (FTP) for measuring emissions from newly manufactured vehicles; and
■ measures to ensure that in-use vehicles meet emissions standards, such as inspection and maintenance (I/M) programs and onboard diagnostic systems.
● Oxygenated Fuels Programs
The CAAA required 31 metropolitan areas that exceeded NAAQS for carbon monoxide to implement oxygenated fuels programs. (Other areas with CO problems may "opt-in" to the program.) During the winter months, gasoline sold within these areas must contain a minimum of 2.7 percent oxygen. This is accomplished by adding oxygenates, such as ethanol or MTBE, to conventional gasoline.
As noted earlier, oxygenated fuels reduce CO emissions, a product of incomplete combustion, by helping fuel burn more efficiently. At temperatures above 50｡?, results from dynamometer tests suggest that there could be a 5.4 to 27 percent reduction in CO for fuels with the required levels of oxygenate. An exhaust CO emissions model developed by EPA predicted reductions of 7 to 15 percent for oxygenated fuels containing required levels of MTBE and ethanol. (Rao 1996, table 8) A number of tunnel and remote-sensing studies also reported similar emissions reductions under real-world conditions, although others have not observed significant reductions.
EPA and other agencies conducted studies to determine how these emissions reductions affect air quality levels. An EPA analysis of CO concentrations from 1986 to 1994 concluded that the oxygenated, fuels program implemented in 1992 reduced average CO concentrations by 3.1 to 13.6 percent, or an average of about 8 percent. (Cook et al 1996) Other studies showed similar results. (Dolislager 1993; Mannino and Etzel 1996)
In spite of emissions reductions observed in controlled tests and apparent air quality improvements due to the oxygenated fuels program, reservations exist about the benefits of oxyfuels and there are some concerns regarding the potential adverse effects of some oxygenates. Criticisms include:
■ Actual CO reductions are uncertain. There is only limited test data on CO emissions from vehicles using oxyfuels at temperatures below 20°F, even though many cities in the program experience winter temperatures this cold. Most emissions tests have been performed under an ambient temperature of 75°F. (NRC 1996, 34-35) Also, large reductions in ambient CO concentrations have been observed in some areas without oxyfuels programs, while increases have been observed in some areas with these programs. (NRC 1996, 37-40)
