CLOVIS, Calif. — The San Joaquin Valley in central California has some of the worst air pollution in the country. Clovis Unified School District, which serves a 200-square-mile area, sits amid this squalid air. The district operates 80 buses and transports more than 5,000 children daily.

With a $287,000 grant from the EPA Clean School Bus USA program, the district retrofitted 50 buses with either diesel oxidation catalysts, diesel particulate filters (DPFs) or inline oxidation catalysts and began using an emulsified fuel called PuriNox that is 79 percent diesel, 20 percent water and 1 percent additive. In addition, a few of the buses are using ultra-low sulfur diesel fuel.

After the first year of the demonstration project, Joe Bjerke, Clovis’ transportation director, says the results have been good.

Bjerke says he was able to outfit 50 buses ranging in age from 5 to 20 years with emissions-reduction hardware. Five of the newer buses in the fleet were retrofitted with DPFs and began using ultra-low sulfur diesel fuel. The district also operates 21 compressed natural gas buses.

In some cases, the emissions-control devices, manufactured by Engine Control Systems, a division of Lubrizol Corp., had to be modified to work with the mix of buses in the Clovis fleet. “They had to send their engineers a time or two,” Bjerke says. But the modifications were successful, and he’s happy with the results.

The buses that operate on PuriNox have seen a 12 percent overall reduction in fuel economy, however. And the buses with DPFs need to have the filter element removed and cleaned every 6,000 miles, because the engines don’t generate enough heat to regenerate the filter. But Bjerke says the additional effort is worth the dividends in cleaner air.

“This has been a very positive experience for us,” Bjerke says. “Our district is always looking for ways to improve air quality. We’ve gotten positive feedback from members of the community. They ask how we were able to get rid of the smoke from the tailpipes.