Landmark Study Finds Asphalt Pavement Emissions More Than 250 Times Lower Than Previously Reported

A new peer-reviewed study led by researchers at the University of California, Riverside (UCR), with support from leading experts across the asphalt industry, finds that emissions from asphalt pavements are minimal, highly localized and more than 250 times lower than previously reported. The study found that the measured emissions are a surface-related phenomenon observed under real-world conditions, rather than a bulk material emission.

Published in American Chemical Society Environmental Science & Technology Air (ACS ES&T Air), the study combined controlled laboratory testing with measurements from in-place pavements exposed to environmental conditions. Laboratory testing used representative asphalt pavement samples under realistic temperatures and full-spectrum solar exposure. The researchers also evaluated the formation of secondary organic aerosols (SOAs), particles that can form when emitted chemicals react in the atmosphere. The results showed that measured emissions were primarily associated with the pavement surface rather than the bulk asphalt material.

By evaluating both compacted pavement samples and in-place road surfaces, the researchers examined emissions under conditions designed to better reflect how asphalt pavements behave in service. The findings offer an additional perspective on previous research that estimated substantially higher emissions from asphalt materials. Much of that earlier work relied on laboratory measurements of small, uncompacted asphalt samples rather than real-world, in-place pavement.

“This research brought together academia and industry to better understand potential sources of atmospheric emissions from compacted roadways,” said David Cocker, professor and chair of UCR’s Department of Chemical and Environmental Engineering and lead researcher on the study. “By combining controlled laboratory testing with measurements from in-place pavements, we were able to evaluate emissions using a more comprehensive approach that reflects the conditions pavements experience in the environment.”

The research was conducted through UCR’s Marlan and Rosemary Bourns College of Engineering – Center for Environmental Research and Technology (CE-CERT), which provides advanced capabilities for emissions and environmental research. Cocker’s research focuses on atmospheric chemistry, emissions and air quality.

“This research demonstrates the value of credible, independent science in advancing our understanding of asphalt pavement emissions,” said Reed Ryan, president of the Asphalt Institute. “By supporting rigorous, peer-reviewed research, we can help ensure that discussions about asphalt pavement emissions and air quality are informed by accurate data and real-world conditions.”

The research was commissioned by the Asphalt Institute, National Asphalt Pavement Association (NAPA), Eurobitume, the European Bitumen Association, and State Asphalt Pavement Associations Inc. (SAPA).

“Investing in and advancing fact-based, technical research to continuously improve engineering and construction practices is fundamental to NAPA and the asphalt pavement industry. This study adds proof that in-place asphalt pavements do not adversely impact air quality,” said Audrey Copeland, PhD, PE, president and CEO of NAPA. “In partnership with scientists and experts, we are continually seeking to understand our impact and improve our product as well as manufacturing and paving practices. This work advances our understanding and further informs the asphalt pavement industry’s sustainability and emissions goals.”

“These findings provide valuable information for state asphalt pavement associations and the communities they serve,” said Kevin Burke, executive vice president of the Illinois Asphalt Pavement Association and 2026 SAPA chairman. “Our communities deserve straightforward, fact-based answers to important questions about asphalt pavement emissions, and this research helps advance that understanding.”

Eurobitume Director General Hervé Millet said the research reflects the importance of international cooperation in advancing scientific understanding of asphalt and bitumen.

“This study demonstrates the value of international collaboration in advancing our understanding of environmental performance,” said Millet. “By bringing together expertise, advanced technologies and rigorous analytical methods, the industry can continue to strengthen the scientific understanding of bitumen and asphalt and their role in a more sustainable transportation system.”

Taken together, the findings give regulators, researchers, transportation agencies, policymakers and the public a stronger scientific foundation for evaluating asphalt pavement emissions throughout its service life, and reinforce that in-place asphalt pavement should not be characterized as a significant source of urban smog-forming or other chemical atmospheric emissions based on the conditions evaluated in this study.

The full study, “Primary and Secondary Emissions from In-Service Compacted Hot Mix Asphalt Pavement,” is published in ACS ES&T Air. The study is available at https://pubs.acs.org/doi/10.1021/acsestair.6c00071.