The use of clean fuels and updated pollution control measures in school buses could significantly reduce absences from school, HealthDay reported.

Researchers at the University of Michigan and the University of Washington found that reducing pollution on school buses that 25 million children ride every day could result in 14 million fewer absences from school a year.

Researchers measured the individual impact on children of the federal mandate to reduce diesel emissions and found improved health and less absenteeism, especially among asthmatic children.

"The national switch to cleaner diesel fuel and the adoption of clean air technologies on school buses lowered concentrations of airborne particles on buses by as much as 50 percent," Sara Adar, lead author of the study, said in a statement. "Importantly, our study now shows measurable health improvements from these interventions, too."

For the study, researchers followed 275 Washington state elementary children who rode buses to and from school, before and after their districts adopted cleaner fuels and technologies. Air pollution was measured during 597 trips on 188 school buses from 2005 to 2009, The Laboratory Equipment reported.

Technicians went to the schools to perform monthly measurements to check lung function and inflammation, and child absenteeism from school was recorded.

During these four years, the bus fleet of two school districts was altered with special emissions devices or with the fuel used to power them. Some were fitted with diesel oxidation catalysts or closed crankcase ventilation systems, which are used to reduce tailpipe and engine emissions, respectively. All the buses switched to ultra low sulfur diesel and some used biodiesel. These fuels are projected to reduce particle generation by about 10-to-30 percent, the researchers say.

Researchers observed that switching to ultra low sulfur diesel fuel reduced a marker for inflammation in the lungs by 16 percent over the whole group, and 20 to 31 percent among children with asthma, depending on the severity of their disease.

"Our research also suggests that children riding buses with cleaner fuels and technologies may experience better lung development as compared to those riding dirtier buses," Adar said. "This is consistent with recent findings from the Children's Health Study in California, which reported more robust lung development in children with improvements in outdoor air quality."

The findings are detailed in the American Journal of Respiratory and Critical Care Medicine.