Researchers at Arizona State University found that asphalt emissions increase by up to 46% when humidity rises to 50% at 50°C, releasing toxic volatile organic compounds that form harmful ultrafine particles.
Humidity accelerates asphalt pollution and deterioration
The first study showed that rising humidity triggers a surge in polar VOC emissions from asphalt, which react in the atmosphere to create secondary organic aerosols. Data from over 5,000 observations across 1,400 U.S. road segments spanning three decades revealed that humidity combined with sunlight speeds up asphalt breakdown, leading to a cycle where degradation releases even more pollutants.
Asphalt emits harmful particles day and night
The second study demonstrated that asphalt-derived VOCs produce abundant ultrafine particles smaller than 100 nanometers when exposed to hydroxyl radicals (daytime) and nitrate radicals (nighttime). These particles are small enough to enter the bloodstream directly from the lungs, with night-time chemistry being especially efficient at converting phenolic compounds into particle precursors.
Algae-infused asphalt offers a potential solution
Researchers concluded that removing reactive compounds like catechol from asphalt during manufacturing could significantly reduce harmful air pollution. In Phoenix, Arizona, paved surfaces cover an estimated 40% of the city — enough to blanket San Francisco four times over if concentrated in one area — highlighting the scale of potential impact from cleaner alternatives.
What makes asphalt emissions worse in humid conditions?
Humidity increases the release of polar volatile organic compounds from asphalt by up to 46% at 50°C, which then form secondary organic aerosols and accelerate surface deterioration, creating a feedback loop of pollution.
How small are the particles released from asphalt, and why is that dangerous?
Asphalt emissions form ultrafine particles smaller than 100 nanometers, which are tiny enough to pass from the lungs into the bloodstream, posing risks for respiratory and neurological health.
