School buses are heavy-duty diesel vehicles that can emit significant quantities of diesel-related air pollutants such as fine particulate matter (PM2.5), nitrogen oxides (NOx), and diesel particulate matter (DPM) as they travel to and from our children’s schools. They can also be self-polluting vehicles that expose children on-board to high levels of PM2.5 and DPM. Exposure studies have found that emissions from school bus tailpipes and engine compartments contribute significantly to concentrations of air pollutants on-board school buses. They have also found that air pollution on-board school buses is influenced by local air quality, the density of traffic on the roads traveled, wind direction, the configuration of windows (i.e. open or closed), and idling and queuing patterns.
Exposures studies have found that exposures on-board school buses can be significantly reduced, even under idling conditions, by outfitting school bus tailpipes with emission control devices such as diesel particulate filters (DPFs) and school bus engines with closed crankcase ventilation devices (CCVs). These studies also suggest that on-board exposures can be reduced by keeping doors and windows closed when buses are idling, avoiding idling when buses are waiting in front of schools, and avoiding caravanning on roadways.