As Earth overheats, asphalt is releasing harmful air pollutants in cities

As the world heats up, cities with heat-trapping asphalt and little tree cover have left residents sweltering and breathing in more air pollution.

Asphalt is releasing hazardous air pollutants into communities, especially when hit with extreme heat and sunlight, according to research published in the journal Science Advances on Wednesday. Researchers found that asphalt in California’s South Coast Air Basin emitted more secondary organic aerosols in the summer than gas and diesel motor vehicles combined.

While vehicle emissions are likely to decline in the future, asphalt emissions will likely become worse as cities expand and climate change accelerates. 

The new findings are critical as more frequent and intense heat waves roast neighborhoods that have lots of asphalt and little to no cooling vegetation. 

Over the past 60 years, every decade has been hotter than the last and 2020 is set to be the hottest year on record. The heat and air pollution disproportionately affect poor and marginalized people who are more likely to live in neighborhoods without tree cover but abundant with asphalt pavement. 

In the U.S., where heat kills more people than any other weather event, Black and Latino people are more likely to reside in hot cities.

For example, cities like Baltimore, Dallas and New York have poor neighborhoods that become significantly hotter in the summer than wealthier areas of the same city due to a history of racist housing policies that left formerly redlined minority neighborhoods in hotter parts of town with more industrial activity and highways. 

Researchers heated asphalt to temperatures from 104 degrees Fahrenheit to 392 degrees Fahrenheit and noticed that asphalt emissions persisted at a steady rate after heated with summertime temperatures, which suggests that asphalt continues to release air pollutants even after the summer sun and heat pass. 

“While emissions from some other sources might decrease in the future, the current consumption of asphalt materials and their emissions may remain similar or increase with elevated summertime urban temperatures driven by climate change and urban heat island effects, thus affecting their relative impact on urban air quality over time,” said Drew Gentner, a Yale University professor and author of the study. 

When hit with solar radiation, researchers found that road asphalt releases up to 300% more emissions. 

“That’s important from the perspective of air quality, especially in hot, sunny summertime conditions,” said Peeyush Khare, a researcher at Yale University and another author of the research. 

Researchers said the type of air pollution from asphalt is comparable to vehicle emissions in the city of Los Angeles, which has some of the highest smog levels in the country.

Battling extreme heat, sunlight and wildfires that are made worse by climate change, city officials are scrambling to plant trees for shade and cover hundreds of bus stops.