Asphalt Emissions and a Potential Algae-Based Solution

A series of academic studies has identified that asphalt pavement can release volatile organic compounds (VOCs) into the air, which may contribute to air pollution and pose health risks. Researchers are investigating an algae-based additive that preliminary tests indicate can reduce the toxicity of these emissions. A pilot project is planned to test the material on a city street.

Research on Emissions and Health Impacts

Studies led by researchers affiliated with Arizona State University, published in journals including the Journal of Hazardous Materials and Science of the Total Environment, have analyzed emissions from bitumen, the petroleum-based binder in asphalt.

The research indicates that VOCs released from asphalt can form ultrafine particles, which may affect air quality. One study found that humidity is a significant factor, with an increase in relative humidity raising emissions of certain VOCs by up to 46% at 50°C. Humidity was also found to accelerate asphalt deterioration in sunlight.

Another study demonstrated that asphalt emissions can form ultrafine particles under both day and night conditions, with night-time chemistry being particularly efficient at consuming certain precursor compounds. High humidity was observed to slow, but not prevent, this particle formation.

Potential Health Effects

Regarding health impacts, the research suggests:

Short-term exposure to asphalt emissions can cause dizziness and difficulty breathing.
Long-term exposure may elevate the risk of lung cancer, particularly for construction workers.
As asphalt ages and breaks down, it can release different, more toxic VOCs. Modeling analyses suggest these compounds have the potential to cause neurological damage.

Researchers state that more investigation is needed to determine specific unsafe levels of exposure to these asphalt-emitted VOCs.

Urban Context and Scale

The research is particularly relevant to urban areas with extensive paved surfaces. In Phoenix, Arizona, it is estimated that approximately 40% of the city is covered by roads, parking lots, and other paved surfaces. These surfaces also absorb and release heat, contributing to the urban heat island effect, which researchers note can exacerbate asphalt emissions.

Development of an Algae-Based Additive

In response to the findings, researchers are developing alternative materials. A collaboration between Arizona State University senior scientist Elham Fini and the Arizona Center for Algae Technology and Innovation is focused on creating an algae-based additive for asphalt.

The process involves:

Growing a special strain of algae using wastewater from a Phoenix treatment plant.
Processing the algae through high-temperature baking without oxygen to create a bio-binder.

A study on this material reported that while the algae-infused asphalt did not significantly reduce the total volume of VOC emissions, it reduced the overall toxicity of those emissions by approximately 100-fold.

The algae additive is also reported to help pavement resist breakdown, which could lower long-term maintenance costs.

Next Steps and Further Research

A partnership with the city of Phoenix is underway to pave a test section of road with the algae-infused asphalt for real-world evaluation. Researchers note that VOCs from pavement are often not included in standard air quality assessments, making such testing important.

Researchers are also exploring other alternative binder materials, including a product made from forest-thinning byproducts. A broader suggestion from the research is that removing reactive compounds from asphalt during the manufacturing process could reduce harmful air pollution.