New Health Hazards Linked To Highways

by Wendy Hunter

The studies -- published in the Journal of the Air and Waste Management Association and in Atmospheric Environment -- show that proximity to a major freeway or highway dramatically increases exposure to "ultrafine" particles (tiny particles less than 0.1 micrometers in diameter), which are linked to neurological changes, mild pulmonary inflammation and cardiovascular problems. The EPA currently regulates particles less than 2.5 micrometers in diameter, and ultrafines represent the very smallest particles inhaled by the public.

Traffic-related air pollution is of great concern to Los Angeles, which has the most severe particle air-quality problem in the United States. The Los Angeles Basin is home to more than 15 million residents and 10 million vehicles contributing to its daily traffic. Motor vehicle emissions represent the most significant source of ultrafine particles. Moreover, recent toxicological studies have shown that ultrafine particles are more toxic than larger particles, potentially leading to increased mortality and illness with increased exposure to particulate matter.

"We believe this is the first study conducted in the United States that provides a detailed spatial profile of ultrafine particles near freeways," said William C. Hinds, UCLA School of Public Health, who co-authored the studies with doctoral candidate Yifang Zhu.

The studies assessed the size-distribution and concentration of the tiny ultrafine particles near major freeways. The first study focused on Interstate 405, one of the nation's busiest freeways, with 93 percent of the traffic composed of gasoline-powered cars. The second study looked at the 710 freeway, which has more than 25 percent of its traffic derived from heavy-duty diesel trucks.

Hinds and Zhu concluded that the number of ultrafine particles downwind near both freeways was approximately 25 to 30 times greater than the number upwind. The number of ultrafine particles dropped rapidly with increasing distance from the freeway.

The studies also examined the concentrations of carbon monoxide (CO), black carbon (BC) and particle mass. Both CO and BC concentrations are closely related to vehicle emissions. Like ultrafines, CO and BC concentrations decreased significantly (70 percent to 80 percent) within the first 330 feet downwind of the freeway. This confirms the notion that vehicular exhaust is a major source of these pollutants near a major roadway.