There are environmental benefits and drawbacks associated with using diesel fuel. The benefits of diesel fuel include better fuel economy than regular gas and less emissions from a cold start.
However, vehicles that use diesel fuel also produce more fine particles (particulate matter). These particles pose a threat to human health being linked to aggravating and sometimes causing respiratory illnesses such as asthma.
Diesel engines power most of the nation's trucks, buses, trains, ships, and off-road machinery. But each diesel engine can produce tons of air pollutants over its lifetime. With mounting evidence that diesel exhaust poses major health hazards, reducing diesel pollution has become a public priority.
Most diesel engines used today power heavy vehicles
such as freight trucks, buses, construction and agricultural equipment,
trains, and barges. Diesel passenger vehicles make up only a small share
of the current US market, but automakers are working to reintroduce diesel
engines into sport utility vehicles, pickups, and passenger cars. While
diesel cars are more efficient than their gasoline counterparts, regulations
permit them to emit far more pollutants. Such a tradeoff between efficiency
and clean air is both unwise and unnecessary.
Particulates irritate the eyes and nose and aggravate
respiratory problems, including asthma, which afflicts 13 million Americans.
Very small particles, called fine particulates, have also been directly
associated with an increased risk of premature death. One recent landmark
study found that the risk of premature death in areas with high levels
of fine particulates was 26 percent greater than in areas with lower levels.
Researchers estimate that, nationwide, tens of thousands of people die
prematurely each year as a result of particulate pollution. Diesel engines
contribute to the problem by releasing particulates directly into the
air and by emitting nitrogen oxides and sulfur oxides, which transform
into "secondary" particulates in the atmosphere.
In addition to contributing to mainstream air pollution problems, public health agencies consider diesel exhaust a potential human carcinogen. Exposure to high levels of diesel exhaust causes lung tumors in rats, and studies of humans routinely exposed to diesel fumes indicate a greater risk of lung cancer. For example, occupational health studies of railroad, dock, trucking, and bus garage workers exposed to high levels of diesel exhaust over many years consistently demonstrate a 20 to 50 percent increase in the risk of lung cancer or mortality. The International Agency for Research on Cancer classifies diesel exhaust as a probable human carcinogen, and the US Environmental Protection Agency has proposed the same classification. The California EPA estimates that 450 out of every million Californians are at risk of developing cancer due to diesel exhaust exposure.
The public-health problems associated with diesel emissions
have intensified efforts to develop viable solutions. But while improvements
to existing diesel engines and fuels are necessary, they are not a long-term
solution. Alternative fuels and advanced engines can provide larger gains.
Fortunately, these new low- or no-pollution technologies are winning acceptance
as alternatives to major new investments in diesel-based solutions.
Light vehicles. While diesel powers relatively few automobiles or light trucks today, industry and government are currently working to reintroduce this technology into passenger vehicles to meet fuel economy and climate change goals. But advanced technologies such as battery, hybrid, and fuel cell electric vehicles powered by alternative fuels provide better solutions to air quality, climate change, and energy security problems. Research into advanced vehicles should therefore focus on these inherently cleaner choices. At a minimum, regulators should close historic loopholes that permit diesel cars to pollute more than those powered by gasoline. Government policy should also target the largely untapped potential for improving gasoline vehicles while working to help bring truly clean and efficient vehicles to market.
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