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Dirty diesel?

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I’ve long thought the Volkswagen Golf, now in its fourth generation as the car that replaced the Beetle, was an inherently brilliant, space-saving design. It was quite influential on a whole range of 1980s hatchbacks, which now seem to be making at least a modest comeback.

The latest Golf is quite fun to drive, offers usable rear seats despite being amazingly compact, and even includes a trunk. The Golf TDi is something else again, powered by a very fuel-efficient turbodiesel engine that yields nearly 50 miles per gallon. It has many of the gas-saving advantages of the Honda and Toyota hybrid cars, without the disadvantages of the complex dual drivetrain. But it’s a diesel.

What’s wrong with that, you may well ask? The Europeans love the technology, and Rudolph Diesel’s engine (first run in 1893) could be in 50 percent of Europe’s cars by 2005. More than 3 million diesels are sold over there every year. So why don’t Americans take to them?

In a word, the problem is particulates — little bits of matter that can lodge in the lungs and cause cancer. Today’s diesels have many improvements, including quick starting and rapid acceleration. But the particulate problem is still with us.

According to a report from the Boston Public Health Commission, "Diesel engines emit large volumes of pollutants into our cities daily. Diesel engines account for 44 percent of nitrogen oxide emissions and 69 percent of particulate emissions from transportation. Nitrogen oxides irritate and damage lung tissue, and particulates are considered by many to be carcinogenic."

The California Air Resources Board in 1998 labeled diesel particles as a "toxic air contaminant and probable human carcinogen." The Environmental Protection Agency has declared that exhaust from diesel engines accounts for 78 percent of the total added cancer risk in outdoor air from all hazardous air pollutants combined. A recent study from the South Coast Air Quality Management District of California concluded that 70 percent of the total cancer risk from vehicles was attributable to diesel particulates.

The Green Guide to Cars and Trucks notes that the 1.9-liter TDi version of the Volkswagen Beetle (with the same engine as the Golf) scores 50-percent higher in fuel efficiency than its gas-powered counterpart. But the book gives the Golf an "inferior" rating nonetheless. "It is still an open question whether diesel engines can be made clean enough to extensively exploit their efficiency advantage in the U.S. market," it says. "The EPA allows the diesel version (of the Beetle) to emit five times as much nitrogen oxide (NOx) pollution as the gasoline-powered New Beetle."

Diesels are getting better. Ford, as an example, has developed a catalytic, soot-trapping filter to remove fine particles, and another to reduce NOx. These technologies aren’t online yet, but diesels will have to meet tough new 2007 emissions standards if they are to remain on the U.S. market.

They’re working on it. The industry group Diesel Technology Forum claims, "With the TDi technology, the stereotype of diesel cars as dirty, smoke-spewing vehicles goes right out the window!" A report in Autoweek notes that, by burning less fuel, diesels emit less carbon dioxide. The story adds, "Particulates can be managed with new filters in the exhaust system that have been developed and continue to be developed, but everyone involved with diesel agrees that NOx is the harder nut to crack."

And because of that harder nut, environmentalists remain skeptical about diesels.

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