Sarah Gardner: The World Health Organization announced this week that diesel fumes definitely cause lung cancer. The WHO has labeled diesel as a “known carcinogen.” Not exactly the kind of thing advocates of clean diesel want to hear right now.

Marketplace’s Nancy Marshall Genzer reports on diesel’s brand image and what this latest pronouncement might mean for the fuel.

Nancy Marshall-Genzer: So, who hasn’t run from the stinky wake of a noisy bus or semi? Turns out, there’s a reason to hold your nose.

Frank O’Donnell: It’s like a giant, rolling cigarette, causing risks very much akin to being someone locked in a room with someone else who’s smoking.

That’s Frank O’Donnell, president of Clean Air Watch. He says we’re not just dodging fumes from soot spewing buses and trucks. Trains and boats also use diesel. Diesel engines power construction equipment and tools used by miners.

Allen Schaeffer heads the Diesel Technology Forum, a trade group. He  says the WHO relied too much on studies of old diesel engines in determining that diesel fumes cause cancer.

Allen Schaeffer: In many ways, it feels like a very retrospective look backwards. You know, like looking in the rearview mirror to try and help inform what our policies are today.

Schaeffer says the new diesel engine is very different — it burns cleaner fuel, has emissions controls and filters. But is that going to be clear to consumers thinking about buying a diesel car? Or will they be scared away by the WHO’s cancer warning? Schaeffer says new diesel will not lose its luster.

Schaeffer: I think there’s a very bright future for all kinds of clean diesel technology, from passenger cars to the biggest off-road construction and mining equipment.

But there are still plenty of old diesel engines around to give the new ones a bad name. Frank O’Donnell estimates there are millions in the U.S. because diesel is durable. Engines last up to 30 years.

In Washington, I’m Nancy Marshall-Genzer for Marketplace.