The fresh scent of pine has helped atmospheric scientists find missing sources of organic molecules in the air -- which, it could well turn out, aren't missing after all. In work appearing in this week's Proceedings of the National Academy of Sciences Early Edition Online, researchers examined what particles containing compounds such as those given off by pine trees look like and how quickly they evaporate. They found the particles evaporate more than 100 times slower than expected by current air-quality models.
"This work could resolve the discrepancy between field observations and models," said atmospheric chemist Alla Zelenyuk. "The results will affect how we represent organics in climate and air quality models, and could have profound implications for the science and policy governing control of submicron particulate matter levels in the atmosphere."
Zelenyuk and colleagues at the Department of Energy's Pacific Northwest National Laboratory were able to measure evaporation from atmospheric particles in a much more realistic manner than ever before. This allowed them to show that they are not liquids, as has been assumed for two decades, and to get an accurate read on how fast these particles evaporate. What researchers previously thought takes seconds actually takes days.
Secondary organic aerosols are tiny bits of chemically modified organic compounds floating in the air. They absorb, scatter or reflect sunlight, and serve as cloud nuclei, making them an important component of the atmosphere.
For a couple of decades, researchers have interpreted laboratory and field measurements under the assumption that these particles are liquid droplets that evaporate fast, which is central to the way these particles are modeled. However, to this day researchers have failed to explain the high amounts observed in the real atmosphere. The never-ending search for extra sources of organics has been frustrating for scientists studying these aerosols.
To re-examine the assumption, researchers at PNNL used equipment that could study the particles under realistic conditions. Zelenyuk developed a sensitive and high-precision instrument called SPLAT II that can count, size and measure the evaporation characteristics of these particles at room temperature. Research and development for SPLAT II occurred partly in EMSL, DOE's Environmental Molecular Sciences Laboratory at PNNL.
First, the researchers created secondary organic aerosol particles in the lab by oxidizing alpha-pinene, the molecule that makes pine trees smell like pine. Oxidation is the same thing that happens to iron when it rusts, and happens a lot in the atmosphere when aerosols come into contact with gases such as ozone, which is a pollutant when it is low in the atmosphere.
For comparison, the researchers also made particles from other, well-understood organic molecules that are known to form solids or liquid droplets, such as one called DOP. Lastly, they allowed these other organic molecules and the pine-scented SOA particles to mingle to simulate what likely happens in the outdoors.
Monitoring the various particles with SPLAT II for up to 24 hours, the research team found that DOP particles behaved as expected. Organics evaporated from the particles quickly, and faster if the particle was smaller, which is how liquid particles evaporate.
But the pinene-based particles did not. About 50 percent of their volume evaporated away within the first 100 minutes. Then they clammed up, and only another 25 percent of their volume dissipated in the next 23 hours. In addition, this fast-slow evaporation occurred similarly whether the particle was big or small, indicating the particles were not behaving like a liquid.
This lack of evaporation could account for the inability of scientists to find other sources of atmospheric organics. "Our findings indicate that there may, in fact, be no missing SOA," said Zelenyuk.
In the world, the SOAs from pinene co-exist with other organic molecules, and some of these slam onto the particle and coat it. Experiments with the co-mingled SOAs and organic compounds showed the researchers that coated particles evaporate even slower than single-source SOA.
Zelenyuk then tested how close to reality their lab-based SOAs were. Using air samples gathered in Sacramento, Calif., the team found the behavior of atmospheric SOAs (whether from trees and shrubs or pollution) paralleled that of the co-mingled pinene-derived SOAs in the lab and did not behave like liquids.
The results suggest that in the real atmosphere, SOA evaporation is so slow that scientists do not need to include the evaporation in certain models. The researchers hope that incorporating this information into atmospheric models will improve the understanding of aerosols' role in the climate.
More on http://www.emsl.pnl.gov/news/viewArticle.jsp?articleId=106">SPLAT II
More on the Sacramento CARES campaign
Reference: Timothy D. Vaden, Dan Imre, Josef Beránek, Manish Shrivastava, and Alla Zelenyuk, On the Evaporation Kinetics and Phase of Laboratory and Ambient Secondary Organic Aerosol, Proc Natl Acad Sci U S A, Early Edition online the week of January 24, DOI 10.1073/pnas.1013391108 (http://www.pnas.org/cgi/doi/10.1073/pnas.1013391108).
This work was supported by the U.S. Department of Energy Office of Science.
EMSL, the Environmental Molecular Sciences Laboratory located at Pacific Northwest National Laboratory, is a national scientific user facility sponsored by the Department of Energy's Office of Science. EMSL offers an open, collaborative environment for scientific discovery to researchers around the world. EMSL’s technical experts and suite of custom and advanced instruments are unmatched. Its integrated computational and experimental capabilities enable researchers to realize fundamental scientific insights and create new technologies. EMSL's Facebook page.
Pacific Northwest National Laboratory is a Department of Energy Office of Science national laboratory where interdisciplinary teams advance science and technology and deliver solutions to America's most intractable problems in energy, national security and the environment. PNNL employs 4,900 staff, has an annual budget of nearly $1.1 billion, and has been managed by Ohio-based Battelle since the lab's inception in 1965. Follow PNNL on Facebook, LinkedIn and Twitter.
Mary Beckman | Newswise Science News
Scientists produce a new roadmap for guiding development & conservation in the Amazon
09.12.2016 | Wildlife Conservation Society
Successful calculation of human and natural influence on cloud formation
04.11.2016 | Goethe-Universität Frankfurt am Main
Physicists of the University of Würzburg have made an astonishing discovery in a specific type of topological insulators. The effect is due to the structure of the materials used. The researchers have now published their work in the journal Science.
Topological insulators are currently the hot topic in physics according to the newspaper Neue Zürcher Zeitung. Only a few weeks ago, their importance was...
In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.
Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...
Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
09.12.2016 | Life Sciences
09.12.2016 | Ecology, The Environment and Conservation
09.12.2016 | Health and Medicine