Report: Filtration System Reduces Pollutants Inside the Bus


A recent study by researchers at the UCLA Fielding School of Public Health concluded that a filtration system designed especially for use in school buses can diminish on-board pollutants by up to 88 percent.

“School buses are by far the safest way to transport children between school and home,” said Yifang Chu, senior author of the study and associate professor at UCLA’s department of Environmental Health Sciences. “Our goal is to make it also the cleanest way.”

Researchers designed a prototype high-efficiency cabin air (HECA) filtration system and installed two units in the rear of six school buses used for testing. The units drew in air through diffusers located on its sides of the bus and passed the air through the HECA filters. Researchers tested the air inside and outside the buses for emissions such as black carbon and fine as well as ultrafine particles.

The study, funded by the California Air Resources Board, tested buses without passengers both while they were parked and while they were running on major arteries and highways in the Los Angeles area.

Interestingly, researchers found that the decrease in pollutants was greater in freeway driving conditions. This was surprising due to the higher concentration of pollutants that come from the highly congested Los Angeles freeways. The study stated that the quality of the filtered air inside the bus was comparable to that of the beach in Santa Monica, California.

According to Zhu, exposure to pollutants can take a toll on children’s health.

“During school bus commuting, children can be exposed to significantly greater levels of air pollutants than a typical resident in the South Coast air basin,” she said. “Studies have shown that exposure to high levels of vehicle pollution is associated with pulmonary and cardiovascular health risks, including oxidative stress, mitochondrial damage and acute pulmonary inflammation.”

UCLA said in a statement that another study funded by CARB over a decade ago found “air quality problems” inside diesel-powered school buses. 

“That study led to efforts to retrofit school buses with exterior pollution-reducing devices. While that method is promising for minimizing emissions from buses’ tailpipes, it doesn’t always provide cleaner air inside the buses,” the statement read.

A prior study also conducted by Zhu and her team found that air purifiers designed for home use can decrease levels of pollution inside the school bus by approximately 50 percent. However, these filters are not designed for use inside moving vehicles.

A long-term follow-up study will test the HECA systems on a greater number of school buses with children on board.

airflowPhoto: UCLA