The wheels on the bus go round and round, each day transporting 24 million American children to and from school. The results of a recent study, however, suggest that the young passengers on those 600,000 buses might have a little less to sing about.

One of the most prominent authors of the study, Yale School of Forestry and Environmental Studies professor John Wargo, said the study “identifies children’s exposure to diesel exhaust in school buses and their hazards.” The study’s results suggest this potential harm is especially serious for children suffering from respiratory illness, because the diesel exhaust can cause inflammation of airways.

Wargo represented Yale at a press conference held last Thursday at the Legislative Office Building in Hartford, where the researchers released the study’s findings. He was also featured on the Thursday edition of “Good Morning America.”

Currently, the threshold for safe exposure to diesel exhaust is unknown. The study points to bus emissions as not only dangerous for those already with respiratory illness, but also as a cause of illness itself.

According to the Centers for Disease Control and Prevention, 4.8 million children in the United States suffer from asthma. Connecticut is home to over 44,000 of these children. The fuel that powers their big yellow school buses each day contains 40 chemicals listed as hazardous air pollutants in the federal Clean Air Act. A known carcinogen, benzene, is one of the chief components of the exhaust.

During the study, over 75 bus runs were tested. Of those tested, 27 of the runs were conducted along an experimental route; all vehicles’ interior concentrations exceeded Connecticut’s standard for fine particulate matter. The levels of the fuel were highest while the buses were stopped to pick up students.

Wargo spoke about the findings on “Good Morning America.”

“For short periods of time, we were finding levels five to 10 times higher than the government standard,” he said on the show. “It was a surprise to me.”

Another component of the tests involved comparing the air quality children breathed at different times of day. Wargo gave schoolchildren ultrasensitive monitors, which took readings of the air quality around them every 10 seconds over the course of the school day. The results supported the researchers’ hypothesis: air quality is worst during their trips to and from school.

“In the morning when they got on the bus, they were exposed to a high intensity of particulates,” Wargo said on “Good Morning America.” “They tended to diminish during the school day, and then at the end of the day there was another burst of their exposure.”

Wargo said there are several measures the state can take to reduce the potential harm to children. The suggestions include keeping the bus wheels moving by prohibiting idling, keeping the windows open whenever possible, and enforcing limits on the amount of time children spend in buses. He also suggested employing the cleanest buses on the longest pickup and drop-off routes.