The lead author of the research team, John Wargo, Ph.D., Professor of Risk Analysis and Environmental Policy at Yale University's School of Forestry and Environmental Studies and Department of Political Science, said, “Children are exposed to diesel exhaust from school buses at levels far above those predicted by current government monitoring efforts.” The team collected data using small portable monitors carried by children through their school days. Air quality monitoring was conducted by the University of Connecticut's Environmental Research Institute.

The research team found that fine particulate concentrations (PM2.5) measured on diesel buses were often 5-10 times higher than average levels measured at the 13 fixed-site PM2.5 monitoring stations in Connecticut. Levels of fine particles and black carbon were higher under certain circumstances: when buses were idling with doors or windows opened; when buses moved through intense traffic; when buses followed other diesel vehicles; and especially when buses were queued to load or unload students while idling. Particle and black carbon levels on buses powered by natural gas were not distinguishable from background levels.

David Brown, Sc.D., a toxicologist with the Northeast States for Coordinated Air Use Management (NESCAUM) and study collaborator, said, “Diesel exhaust is comprised of very fine particles of carbon and a mixture of gases, including benzene, formaldehyde, 1,3- butadiene and acetaldehyde. These are well-recognized toxic substances. Most federal health authorities, including the National Toxicology Program and the EPA, have designated the components of diesel exhaust as human carcinogens. They are also genotoxic, mutagenic, and can produce symptoms of allergy, including inflammation and irritation of airways."

The Environmental Protection Agency adopted new diesel regulations in 2000. The revised rules will eventually require reduced emissions from newer engines and the use of ultra low sulfur fuel. The rules will not be fully implemented until 2010, and even then older diesel vehicles will still be in use. In announcing the new requirements the Agency said, “Today's action will prevent 8,300 premature deaths, 5,500 cases of chronic bronchitis, and 17,600 cases of acute bronchitis in children. It will also avoid over 360,000 asthma attacks and more than 386,000 cases of respiratory symptoms in asthmatic children annually. The action will prevent 1.5 million lost work days, 7,100 hospital admissions and 2,400 emergency room visits for asthma every year.”

Reflecting on these statistics, Professor Wargo said, “The tougher diesel regulations adopted by EPA last year are important, but insufficient to protect the respiratory health of children today. EPA's estimates did not account for the high exposures experienced daily by children while riding school buses, or from indoor pollution in homes, schools, and occupational settings. It seems unreasonable to wait any longer before taking steps to minimize diesel emissions from school buses.”

Mark Cullen, M.D., Professor of Medicine and Public Health at the Yale School of Medicine and director of Yale's Occupational and Environmental Medicine Program, and participant in the research, recently found that asthma prevalence within individual Connecticut schools ranged between 3 percent and 20 percent, in a study that was also sponsored by EHHI. Dr. Cullen said, “Although we do not fully understand the relation between diesel exhaust and asthma prevalence, we do know that components of diesel exhaust can adversely affect lung function in children with underlying respiratory illnesses such as asthma, bronchitis, and infections. Children's airways are not yet fully developed and have a smaller diameter than those of adults. Given these conditions, it may be more difficult for asthmatic children—with restricted airways—to clear the very fine particles and gases inhaled deeply within their lungs.”

Robert LaCamera, M.D., Clinical Professor of Pediatrics at the Yale School of Medicine and a reviewer of the study, commented, “There is no known safe level of exposure to diesel exhaust for children, especially those with respiratory illness. The Centers for Disease Control and Prevention estimates that 4.8 million U.S. children have asthma. This figure includes the nearly 44,500 school-aged children in Connecticut diagnosed with the illness, and most of these children ride the bus to school. Therefore, I strongly support efforts to reduce diesel emissions from school buses as soon as possible.”

The research team found that within the United States nearly 600,000 school buses transport 24 million students to school daily. In Connecticut, 387,000 students ride to school on nearly 6,100 buses. If rides average 30 minutes in each direction, students will spend 180 hours on buses each year. Collectively, U.S. children spend 3 billion hours on school buses each year.

Background air pollution is already a serious problem in Connecticut and in many other parts of the nation. In 2001, portions of Connecticut exceeded the federal ozone limit on 26 days, as reported by the Connecticut Department of Environmental Protection. Diesel exhaust includes nitrogen oxides and volatile organic compounds that together contribute to ozone levels that may exacerbate asthma.

Susan Addiss, former Connecticut Commissioner of Health and Vice President of the Connecticut Health Foundation, noted, “This study reveals that children are exposed to toxic air pollutants at levels not yet accounted for by federal or state officials. These are preventable threats to children's respiratory health that could be reasonably managed by following the recommendations suggested in this study.”

“This study shows that it is incredibly important to prohibit unnecessary school bus idling and to have this prohibition include local enforcement,” said Nancy Alderman, President of Environment and Human Health, Inc. “This study also shows the importance of requiring the use of low sulfur fuel and retrofitting school buses with both particle traps and catalytic converters. If we start with these few recommendations we will be taking a large step toward protecting children's health.”