According to the results of a five-year study by researchers at New York University's School of Medicine, the unusually high numbers of elementary school children suffering from asthma and other respiratory ailments in the South Bronx area of New York, can be attributed to motor vehicle exhaust fumes.
The researchers say soot particles from the exhaust of diesel trucks is to blame for the alarming rise in asthma in children attending school which are close to busy truck traffic routes.
It seems that on days when the traffic is particularly heavy the children's asthma symptoms, in particular wheezing, doubled because of the high concentrations of air pollution.
For the study period the children carried air pollution monitors in their backpacks as they went to and from school, and it was found that all of the children were exposed to tiny particles smaller than 2.5 microns (PM2.5) ranging from 20 to 50 micrograms per cubic meter.
The Environmental Protection Agency's suggested daily limit of 35 micrograms per cubic meter was exceeded on about one-third of the study days.
Although only around 10 percent of the total mass of tiny particles was diesel soot, it was this that was most closely linked to the children's asthma.
Particles smaller than 2.5 microns have been mostly closely linked to lung and heart disease and the EPA has regulated PM2.5 since 1997, limiting each person's average exposure per year to no more than 15 micrograms per cubic meter.
Other studies have also found that people living near highways have a higher incidence of asthma, but until now the actual levels of traffic air pollutants that individuals were being exposed to had not been measured.
George Thurston, Sc.D., Associate Professor of Environmental Medicine at NYU School of Medicine, one of the study's principal researchers, says the study confirms that diesel soot particles in air pollution are exacerbating asthma in children.
The main culprit was found to be elemental carbon also called black soot, which is found in diesel exhaust and is smaller than 2.5 microns.
This particular type of carbon has been found in other studies conducted in a laboratory, to be a cause of asthma.
The South Bronx area of New York has some of the highest incidences of asthma hospital admissions in New York City, and it is surrounded by several major highways.
Dr. Thurston says the study shows that the children are being exposed to very high fine-particle concentrations on a fairly regular basis, and diesel exhaust fumes appear to be particularly damaging.