Auto emissions are a key factor in the creation of tiny matter called ultrafine particles and pose a significant health problem in many urban areas, according to a new study.

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

Their findings show that auto exhaust plays a part in the creation of large amounts of the particles, no wider than one-thousandth of a human hair. These tiny particles are a proven harmful contributor to air quality and human health and have been linked to birth defects.

“This has been an emerging area for research,” says Renyi Zhang, a professor of atmospheric sciences and the chair in geosciences at Texas A&M University. “Ultrafine particles can penetrate easily through human lungs and reach many vital organs. 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 air quality standards established by the US Environmental Protection Agency (EPA) only limit the mass concentration of PM2.5—referring to particles smaller than 2.5 microns—for human health concerns. Ultrafine particles make up little PM2.5, because of their negligibly small masses. They are produced more efficiently when the atmospheric PM2.5 levels are low, according to this study.

“Our measurements are representative of typical urban environments worldwide since the gasoline fleet of the commonly used vehicle model in China is equivalent to those in Europe and the United States,” the researchers write in the paper.

“The problem of ultrafine particles is as important in China as in the US. Reduction in PM2.5 to improve air quality could exacerbate pollution of ultrafine particles,” Zhang says.

The implementation of the Clean Air Act in 1990 has led to a noticeable reduction in PM2.5 over the United States.

“Protecting the public health needs simultaneous reduction in both types of particles,” Zhang says. “Sound science is essential to guide the regulatory policies.”

While finding ways to reduce the ultrafine particles will require much more research, Zhang says drivers using electric cars would almost certainly help. But that could be years in the future since electric vehicles currently make up less than 1% of over a billion vehicles on roads worldwide.

The study shows for the first time “that traffic emissions are a major source for ultrafine particles. Our studies show that aromatic organic compounds from auto exhaust form these ultrafine particles. They form in any cities from car exhaust, such as Houston, New York City, and Washington, DC. Residents who live close to highways or congested roads are particularly vulnerable,” Zhang says.

“This is a frontier area in air pollution. Producing close to 1 million nanoparticles per cc in air is a serious matter of concern,” he says.

The research appears in the Proceedings of the National Academy of Sciences.

Funding for the study came from 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.

Additional researchers are from the University of Texas at Austin; the University of California, San Diego; California Institute of Technology; Johns Hopkins University; and several Chinese universities.

Source: Texas A&M University

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