Though the tiny size of diesel exhaust particles may contribute to their ability to penetrate all areas of the body, Sun noted that their complex chemical composition, and the way in which those chemicals are released once particles enter the body, also influence how they react with human cells.

Gasoline exhaust particles are larger than diesel fume particles, but it's premature to suggest that they are any less dangerous to humans, Sun said.

"The bigger particles are known to be harmful primarily for upper respiratory tract illnesses. Larger particles also can't travel long distances they tend to fall to the ground," he said. "Smaller particles hover in the air for a long time and can have long-term impact on humans when inhaled."

Sun and colleagues are now conducting a study testing whether the exhaust particles promote tumor development and metastasis.

This work is supported by Health Effects Institute awards and grants from the National Institutes of Health.

Co-authors on the study are Xiaohua Xu and Ling Zheng of Ohio State's Division of Environmental Health Sciences; Nisharahmed Kherada, Aixia Wang and Sanjay Rajagopalan of the Davis Heart and Lung Research Institute; Xinru Hong of the Department of Obstetrics and Gynecology at Fuzhou General Hospital in Fujian Province, China; Chunli Quan, Morton Lippmann and Lung Chi Chen of the Department of Environmental Medicine at the New York University School of Medicine; and Loren Wold of the Center for Cardiovascular and Pulmonary Research at Nationwide Children's Research Institute.

Source: Ohio State University