Here’s an excerpt, read more at Bilal’s blog.

Bilal Zuberi, a recently-minted Ph.D. in chemistry, whose work with Nobel laureate Mario Molina re-examines a problem that literally hangs heavy in the air of some of the world’s most populous cities.

“Today, you cannot go to Mexico City, you cannot go to Delhi, you cannot go to Bombay, you cannot go to Beijing and tell them to buy fuel-cell cars,” Zuberi says. “Today they drive diesel vehicles; today they drive scooters. And you’ve got to clean that up.” The smog that darkens megacities’ skies comes in no small part from tiny, inefficient engines such as the ones that power the 200 million motor-scooters around the planet. One of these two-stroke engines can spit out as much smog-creating, respiratory-aggravating particulates as 50 trucks coming off American assembly lines today, Zuberi says.

Here comes the pitch: Zuberi’s company GEO2 has developed a $7 filter that takes out 99% of the scooter’s particulate pollution. Same goes for leaf-blowers and other small-engine smog-belchers. (Those can be five times more polluting than even the scooters, he notes.) This big chunk of the third-world smog problem is relateively easy to solve today, Zuberi says, because the last time any serious effort was made to research and mass-produce particulate filters for scooters and other such heavy polluters was the 1970s.

Hopefully the regulators in third-world countries will start paying attention soon.