In more recent times I have become more curious. I have pondered the question of what becomes of air pollutants over time. If not inhaled and absorbed into the lungs, blood or heart, or are in some way breached, what happens to air contaminants?
The Pacific Northwest National Laboratory (PNNL) – a part of the U.S. Department of Energy (DOE) – in collaboration with DOE’s PNNL Environmental Molecular Sciences Laboratory (EMSL) announced in a Nov. 15, 2012 press release, that “an ultra-sensitive instrument that can determine the size, composition and shape of individual particles” had been developed.
This significant breakthrough allows the PNNL research team in question to understand how airborne particles known as secondary organic aerosols or SOAs interact with polycyclic aromatic hydrocarbons or PAHs, for example.
Air pollution insights
“Floating in the air and invisible to the eye, airborne particles known as secondary organic aerosols live and die. Born from carbon-based molecules given off by trees, vegetation, and fossil fuel burning, these airborne SOA particles travel the currents and contribute to cloud formation. Along for the ride are pollutants, the PAHs, that have long been thought to coat the particles on their surface,” PNNL’s Mary Beckman in the release wrote.
“For decades, atmospheric scientists have been trying to explain how atmospheric particles manage to transport harmful pollutants to pristine environments thousands of miles away from their starting point. The particles collected in areas such as the Arctic also pack higher concentrations of pollutants than scientists’ computer models predict.”
The instrument that has the capability to analyze as well as characterize these particles is known as SPLAT II and “can analyze millions of tiny particles one by one,” analysis that can offer unique insight into both particle “property and evolution,” Beckman noted.
But it isn’t just this.
Molecules of pollutants like PAHs, in a sense, hitch rides aboard the SOAs and while in transit, they work their way inside. The two elements thus form a kind of symbiotic relationship which results in a much slower element breakdown or decay than what would normally occur absent this type of kinship.
The scientific team at the PNNL laboratory created two types of particles. Pyrene – “a toxic pollutant produced by burning fossil fuels or vegetation such as forests” – and alpha-pinene – “the molecule that gives pine trees their piney smell” – were the two molecular elements chosen.
On one of the created particles, alpha-pinene was coated with pyrene, which, according to Beckman, “exemplified the classical SOA.” Meanwhile, “The second kind resembled what likely happens in nature: they mixed alpha-pinene and pyrene and let the particles form with both molecules present.” The particles were then sent through the SPLAT instrument and observed over time.
After just four hours, the surface pyrene covering completely evaporated. By day two, due to shrinkage, the alpha-pinene particle was 70 percent smaller, indicating the alpha-pinene SOA had also evaporated but more slowly compared to the surface pyrene.
However, in the second particle, the evaporation rate was far slower leading the research team to conclude: “PAHs become trapped within the highly viscous SOA particles, where they remain protected from the environment. The symbiotic relationship between the atmospheric particles and pollutants surprised [Alla] Zelenyuk [one of the main study researchers]: SOAs help PAHs travel the world, and the PAHs help SOAs survive longer,” Beckman wrote.
This landmark research provides added insight into air-pollutant behavior, at least with regard to certain pollutant types.
Image at top: NASA