Dear EarthTalk: Diesel exhaust from trucks, buses, large ships and farm equipment is especially unhealthy.

 
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Dear EarthTalk: Diesel exhaust from trucks, buses, large ships and farm equipment is especially unhealthy. What progress has been made in curbing diesel pollution?--Jackie Mitchell, Barre, MA

Gasoline-powered passenger cars plying American roads have been subject to strict pollution limits for some three decades already, but only recently have tougher standards for diesel-powered trucks, trains, barges and other soot-belching vehicles gone on the books across the country. Traditionally, older diesel engines produce less carbon dioxide per mile driven than gasoline-powered vehicles, but they produce more of the pollution associated with localized environmental trauma--such as smog and soot in the air--that can trigger respiratory and cardiovascular problems and have been linked to lung and other cancers.

Thanks to the work of the Environmental Defense Fund (EDF), American Lung Association (ALA) and others, though, the U.S. government has adopted increasingly stringent rules governing how much particulate pollution and other toxins are allowed to come out of diesel engines. In 2001, these groups convinced Congress to pass strict new pollution limits on heavy-duty trucks and buses. Three years later similarl standards were applied for non-road vehicles, including construction and farm equipment.

These laws were designed to clean up new diesel engines, but the millions of older diesel engines still on American roads, work sites and waterways continue to cause pollution problems. Newer state laws in California, Texas and New York calling on owners of older diesel vehicles to retrofit their engines with emissions reduction equipment has helped clean the air in those states. And regional public-private partnerships administered by the U.S. Environmental Protection Agency's National Clean Diesel Campaign have also helped put a dent in diesel emissions from the trucking, rail and shipping sectors.

Even though the clean-up of diesel engines...

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