(CN) — Automobiles may become more fuel efficient in the coming decades, but the amount of pollution rising from roadways themselves could be the next threat facing humans.
Sunlight and heat bakes asphalt roads throughout the year, and walkers and bicyclists alike know the struggle of being so close to what feels like a blast furnace in summer.
But aside from the heat, hot asphalt roads produce secondary aerosol pollutants that typically skate by air quality studies. Those emissions amount to a greater quantity of pollutants than the gasoline and diesel motor vehicles using the roadway combined, according to a study published Wednesday in the journal Science Advances.
That dilemma could become a real issue with roadways cooking over longer periods of time as climate change stretches out heatwaves.
The pollutant study compared lab tests where researchers heated road asphalt and compared their results to the summertime conditions of roads in a specific region of Southern California and a freshly paved roadway.
California’s South Coast Air Basin is monitored for air quality management and air pollution. The section of California stretches across multiple counties including Los Angeles, Orange, Riverside and San Bernardino and is home to roughly 17 million people, according to the regulatory agency that tracks the air quality for the region.
Study author Peeyush Khare, from the Department of Chemical and Environmental Engineering at Yale University, and his colleagues found emissions of aerosol precursors were greatest during the summer. More urban sprawl means more pollutants released into the air as more roadways are built — leading to greater emissions in urban areas, according to the study authors.
In a lab setting, researchers heated road asphalt between 104 degrees to 392 degrees. Emissions doubled when the temperature increased from 104 degrees to 140 degrees, which is a typical temperature range for a hot roadway in the summer.
“Yet, the current consumption of asphalt materials and their emissions are likely to remain the same or increase with infrastructure growth and urban temperature increases driven by climate change and urban heat island effects, thus enhancing their relative impact on urban air quality over time,” write the study authors.
Emissions jumped to an average of 70% output per 68 degree increase and while those emissions slowed down over a one-week period, they continued to seep out, especially when exposed to sunlight according to the study. Researchers also studied the effects of a hot summer day on asphalt-containing roofing products, which also saw a complex output of emissions.
Researchers also grabbed a sample of freshly applied asphalt, which saw five to seven times greater emissions than older road asphalt.
Previous studies have shown urban areas undergo the “heat island” effect where a lack of trees, tall buildings and an abundance of roadways can create hotter temperatures when compared to outlying areas. By 2050, urban heat islands are expected to raise the planet’s temperature by 2 degrees according to a 2017 study published in Nature Climate Change.