School buses spew pollution into young lungs.

Reducing school bus emissions could be a cost-effective way to cut children's exposure to diesel fumes. Researchers reached that conclusion after finding that school bus passengers may inhale heavy doses of the vehicle's pollution.

To understand school buses' effects on air quality, Eduardo Behrentz of the University of California, Los Angeles and several colleagues drove six buses of various ages on a total of 16 runs along actual routes in and around Los Angeles. On about half the runs, the bus windows were open.

During the runs, the scientists continuously fed a nonreactive tracer gas, sulfur hexafluoride, to the buses' exhaust systems. Devices at the front and rear of each bus measured the tracer. The scientists then estimated the amount of exhaust particles that passengers would inhale.

On average, the rear of each bus' interior is one-third more polluted than the front, Julian D. Marshall of the University of California, Berkeley and Behrentz report in the April 15 Environmental Science & Technology. Moreover, they found, older buses and buses driven with the windows closed carry more onboard air pollution than other buses do. For example, with the windows open, a 30-year-old bus in the study generated twice as much onboard pollution as a 10-year-old bus did. Closing the windows slightly increased passengers' pollution exposure on a 3-year-old bus but tripled it on the 30-year-old one.--B.H.