Auto Emissions Generate More Dangerous Ultrafine Particles Than Once Thought

An international team of researchers that includes undergraduate chemistry student Annie Zhang from The University of Texas at Austin has found that aromatic compounds from auto emissions play a key role in the creation of tiny airborne particles that pose a significant health problem in many urban areas of the world.

The tiny specks, called "ultrafine particles" (UFPs), are no wider than one thousandth of a human hair and are unregulated according to the World Health Organization. Nonetheless, they are thought to contribute to cardiovascular disease and birth defects. Although auto emissions were already recognized for their role in generating particles smaller than 2.5 microns, called PM2.5 particles, this is the first study to find auto emissions also indirectly contribute to the generation of a large amount of far smaller UFPs, which are less than 0.05 microns wide.

Renyi Zhang, Texas A&M Distinguished Professor of Atmospheric Sciences and the Harold J. Haynes Chair in Geosciences, and colleagues from UT Austin, the University of California-San Diego, the California Institute of Technology, Johns Hopkins University and several Chinese universities published their results this week in the latest issue of PNAS (Proceedings of the National Academy of Sciences).

The team studied auto emissions relevant to urban areas, especially Beijing, which has some of the highest pollution from auto exhaust in the world.

Annie Zhang, senior chemistry major at UT Austin and daughter of Renyi Zhang, began work on the project as a high school summer research intern in her father's lab in 2015.

"A lot of my work involved the analysis of the data we obtained from Beijing, as well as trying to understand the relevance of our data as it related to other urban locations around the world, like Houston," she said. "Prior to this study, people thought that sulfur dioxide was the major secondary source for UFPs, but not many people believed that aromatics from auto exhaust would also be a major contributing secondary source for UFP."

"Ultrafine particles can penetrate easily through human lung and reach many vital organs," Renyi Zhang said. "The impacts of ultrafine particles on human health can be far-reaching. Currently, ultrafine particles are unregulated. They can be present in high concentrations, but you still see blue sky."

The study was funded by the National Natural Science Foundation of China, the Robert A. Welch Foundation, and a collaborative research program between Texas A&M University and the National Natural Science Foundation of China.