Paved surfaces and roofs make up 45% of the surfaces of urban areas. Asphalt is a major component of these surfaces, yet little has been studied about how toxic chemicals that make up the material may be emitted in our everyday lives.
In their recent paper in Science Advances, graduate student Peeyush Khare and Professor Drew Gentner study how various toxic gases are emitted from asphalt. Some of these toxic gases are known as secondary organic aerosols, which means that they emit from reactions occurring within a material. These secondary organic aerosols are a major component of PM2.5 materials, particulate matter that is smaller than 2.5 μm or 30 times thinner than human hair. PM2.5 materials pose major human health risks, because they are so small that they can get deep into lungs, airways, and even the bloodstream. To study such emissions, the researchers placed asphalt samples into a chamber and subjected them to different levels of environmental stresses, such as sunlight or temperature. They then used advanced techniques to characterize the types of chemicals released. According to their findings, asphalt releases double the amount of toxic pollutants when its surface temperature increases from 40°C to 60°C, which is often reached in the summertime, and nearly 300% more when exposed to sunlight as compared to no sun. These increased emissions were observed for asphalt road, roofing, and sealing materials. In total, the asphalt-related sources produce more organic aerosol than gas and diesel on-road vehicles combined.
Asphalt is an important building material, but is often overlooked in terms of the emissions it produces, especially compared to other more standard sources of emissions such as vehicles. Khare and Gentner’s work emphasizes that asphalt-related emissions are an important factor to study and regulate, especially as more and more urban areas are developed and paved. While the emissions behaviors of asphalt are dependent on environmental conditions, the higher emissions resulting from hot and sunny days require that we seriously consider asphalt as a source of pollutants.
Managing Correspondent: Eesha Khare