School buses emit pollution from their diesel engines. Diesel emissions are one of the worst contributors to air pollution. Diesel contains a complex mix of volatile gases and particulate matter. The gases, such as nitrogen oxides, contribute to the formation of ozone, which is harmful to human health and contributes to climate change. The particulate matter or soot that the buses exhaust, contains toxic compounds, which also harm human health and black carbon, and which also contribute to climate change. Other than natural forces such as forest fires, diesel engines are one of the largest producers of particulate pollution. (EPA 2003)
The problem of the air quality of school buses has seen some major attention in the last ten years. A study by Environment & Human Health: Children's Exposure to Diesel Exhaust on School Buses led to changes in the oversight of school bus emissions as well as new legislation regarding the idling of school buses. Researchers had students carry personal and portable monitors to see what pollutants they were exposed to during a school day. They found dramatic variability in levels of particulate exposure, with very high peaks during their school bus commute.
Following the study, New Haven's city and Board of Education joined with partners at the EPA, CT Department of Environmental Protection and the Yale Forestry School to retrofit their school buses with either particle filters or catalytic converters to reduce particle emissions. This work was completed in 2006. As the retrofitted fleet phases out (estimated 2007-2009)
, the newest buses must comply with the EPA's 2007 regulation that mandates low-sulfur fuel and high efficiency emissions controls.
The EPA projects a 90% reduction in PM by 2030 with the newer technology, and a 95% reduction in Nitrogen dioxide, however, it is unclear what assumptions these projections are based on.
These documents forecast a reduction in pollutants emitted by diesel engines while perhaps not addressing the quality of the air that students are breathing during their time ON the school bus. Another problem with current EPA projections is the Agency's focus on particulate matter generally, rather than focusing on the smaller and more dangerous particles. The EPA is projecting a reduction in overall PM without forecasting reductions in the smaller sized particles.
In order to quantify the current exposure associated with school bus travel, we will examine studies of buses using newer technologies. A 2005 study by the "Clean Air Task Force" found that the combination of low-sulfur fuel and a "Spiracle" filter that trapped crankcase emissions virtually eliminated the fine particles within the cabin of the bus.
Subsequent studies in 2008 looked at school bus cabin air pollution in Central Texas and in Washington State. In both cases, buses were running low-sulfur diesel fuel. The technologies varied, but both studies examined the impact of retrofits that included filters and catalysts. The Texas study showed an in-cabin reduction in fine PM between 7-43% when using the Spiracle filter. Their conclusion: "retrofit installation could not always be conclusively linked to the decrease of pollutant concentrations in the bus cabin."
The Washington State study concluded that the PM 2.5 levels aboard the school buses were double to four times the ambient (outdoor) air levels.
Another issue of particular importance to New Haven students regards the ambient air outside buses, at schools and at bus stops. The Clean Air Task force study
and a later (2008) study of the air quality surrounding schools found an increase of PM 2.5 of between 1.8 to 5.7 times the level at a control site.
This would indicate that the ambient air in the vicinity of schools is still significantly polluted despite the advent of vehicular pollution control technology and low-sulfur fuel. This finding is particularly troublesome for New Haven Students who not only breath elevated rates of PM in the schoolyard, but at their bus stops which host a multitude of buses to accommodate the diverse destinations within the same neighborhood. This would differ sharply from the exposure of a student at a suburban or rural stop, where a bus may only travel to that location once in the morning and once in the afternoon.
One of the questions we will try to quantify is, how much does the pollution exposure during bus transport increase symptoms, decrease lung function, and put students at risk for medication and hospital visits. Given that students in New Haven are already much more likely to have asthma, by the time they enter school, our concern here is what type of additional pollution burden the bus ride adds to their underlying condition