Asphalt is a near-ubiquitous substance—it’s found in roads, on roofs, and in driveways—but its chemical emissions rarely figure into urban air quality management plans.

Common road and roofing asphalts produce complex mixtures of organic compounds, including hazardous pollutants, in a range of typical temperature and solar conditions, researchers report.

Decades of research about and regulations of emissions from motor vehicles and other combustion-related sources have resulted in improved urban air quality. But recent studies show that as those efforts succeeded, numerous non-combustion-related sources have become important contributors of organic compounds.

These can lead to secondary organic aerosol (SOA), a major contributor of PM2.5—an important regulated air pollutant comprising particles smaller than 2.5 micrometers in diameter—that have significant effects on public health.

For the study in Science Advances, researchers collected fresh asphalt and heated it to different temperatures.

“A main finding is that asphalt-related products emit substantial and diverse mixtures of organic compounds into the air, with a strong dependence on temperature and other environmental conditions,” says lead author Peeyush Khare, a graduate student in the lab of Drew Gentner, associate professor of chemical and environmental engineering at Yale University.

After some time, the emissions at summer temperatures leveled out, but they persisted at a steady rate. That suggests there are long-term, continued emissions from asphalt in real-world conditions.

The researchers also examined what happens when asphalt is exposed to moderate solar radiation and saw a significant jump in emissions—up to 300% for road asphalt—demonstrating that solar radiation, and not only temperature, can increase emissions.

“That’s important from the perspective of air quality, especially in hot, sunny summertime conditions,” Khare says.

Read the full article about asphalt and air quality by William Weir at Futurity.