Asphalt adds to air pollution, especially on hot, sunny days

[Klaralven]

Asphalt is a near-ubiquitous substance -- it's found in roads, on roofs and in driveways -- but its chemical emissions rarely figure into urban air quality management plans.

A new study finds that asphalt is a significant source of air pollutants in urban areas, especially on hot and sunny days.

Yale researchers observed that common road and roofing asphalts produced complex mixtures of organic compounds, including hazardous pollutants, in a range of typical temperature and solar conditions. The results of their work, from the lab of Drew Gentner, associate professor of chemical & environmental engineering, appear Sept. 2 in the journal Science Advances.

Decades of research about and regulations of emissions from motor vehicles and other combustion-related sources have resulted in improved urban air quality. But recent studies show that as those efforts succeeded, numerous non-combustion-related sources have become important contributors of organic compounds. These can lead to secondary organic aerosol (SOA), a major contributor of PM2.5 -- an important regulated air pollutant comprising particles smaller than 2.5 micrometers in diameter -- that have significant effects on public health.

The researchers collected fresh asphalt and heated it to different temperatures. "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," said Peeyush Khare, a graduate student in Gentner's lab and lead author of the study.

https://www.sciencedaily.com/releases/2020/09/200902152154.htm

With electric cars, streets and highways will need to be made from something else, since asphalt is a byproduct of refining crude oil.

[ret5hd]

1. Anyone that walks down the street on a...

summer day knows this.

[ProfessorGAC]

2. Hardly Noteworthy, Scientifically

There are always low vapor pressure, complex alkenes in asphalt, as well as simple substituted naphthalenes. The former have a very low vapor liquid equilibrium that emits slightly volatile organics into the air over time.
The latter undergo sublimation, going right from solid to gas. Same result.
Asphalt is not all anthracenics, just preponderantly so.
This has been known since before I was an undergrad. That was the early to mid-70s.
It's why asphalt shrinks, cracks & spalls over years, even on very low traffic roads.
This article, from Yale, seems to present this as a breakthrough finding. It's not.

[Klaralven]

3. How many of the anthracenics are carcinogenics?

My recollection is that some multi-ring hydrocarbons are carcinogenic.

[ProfessorGAC]

4. Some Are

Anthracenics, though, have such low vapor pressure that the concentration in air would stay very low.
I'd say we couldn't actually measure them at 6 feet. Maybe at the surface, than use a dispersion model to estimate the nanograms per liter at a meter or 2.
Also, remember that there is a molecular weight limit beyond which human biochemistry cannot affect the organic model. The size varies depending on organic species, and functional group orientation. Many anthracenics would likely be inert to the human body.
Naphthenics, howver, can also have teratogenic effects, but a higher concentration than what is likely to come off asphalt at 75°C. More danger, but still very low risk.
The big health concerns come at refineries where those anthracenics "bottoms" are at several hundred degrees F.
They're cooled using blowers across the conveyor screen, but that air is emitted. It goes to a combustor, but any air leakage likely has a fair concentration of slightly volatile naphtheics.
The 2 refineries I've visited did have organic vapor sensors near the entrance to the combustor intake ducts. But, I don't know if that was good stewardship, or legally mandated environmental mitigation. I'm hoping, at the very least, both!
So, you're concern is valid, but likely an extremely low exposure risk.
The bigger concern is uV and infrared absorbing organics added to the air. Which, or course, has been happening for a 80-100 years, nearly worldwide.

[Klaralven]

5. Enlightening. Thank you.