Cars are sources of urban area pollution for sure; however, it turns out that one aspect of roads that you might have overlooked is actually not as innocent as it might look.
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Asphalt as a source of air pollution
In order to understand the source of secondary organic aerosols (SOA), Yale researchers examined asphalt. SOA are a kind of matter that has been linked to asthma and other public health issues.
The study examined the South Coast Air Basin in California. Asphalt inside a tube furnace was monitored, and heated up to a range of temperatures between 40 degrees Celsius and 200 degrees Celsius (that's 104 to 392 degrees Fahrenheit). With this experiment, Yale researchers were able to determine SOA levels in hot conditions.
A bigger source of SOA than motor vehicles combined
The results were shocking, to say the least: in summer's scorching weather, asphalt turned out to be a bigger source of secondary organic aerosols than gasoline and diesel from motor vehicles combined.
Peeyush Khare, a Ph.D. candidate at Yale and lead author of the study, said, "A main finding is that asphalt-related products emit substantial and diverse mixtures of organic compounds into the air, with a strong dependence on temperature and other environmental conditions."
Especially during hot weather, the researchers saw a jump of 300% in harmful road asphalt emissions.
Yale's chemical and environmental engineer Drew Gentner stated, "To explain these observations, we calculated the expected rate of steady emissions and it showed that the rate of continued emissions was determined by the time it takes for compounds to diffuse through the highly viscous asphalt mixture."
The level of air pollution asphalt can generate
More tests are required to detect the exact level of pollution asphalt can generate, and since paved areas make up 45% of surfaces in U.S. cities and building roofs take up another 20%, this is a subject that needs closer examination.
While motor vehicles do produce more pollution overall, those produced by asphalt are often unreported since they are secondary pollutants. In the road to making motor vehicles more green, we may need to tackle roads as sources of air pollution too.
The research has been published in Science Advances.