Environmental engineers reshape understanding of airborne pollution particles
image:
(From left) Peter Vikesland and Yangyang Liu often work with a confocal Raman microscopy system used to study the chemistry and properties of tiny aerosol droplets in the lab.
view moreCredit: Photo by Courtney Sakry for Virginia Tech.
From sizzling bacon in the kitchen to wildfire smoke in the sky, cooking and pollution release microscopic particles that affect humans' health, the air they breathe, and even weather and climate.
New research from Virginia Tech is poised to upend how scientists think about the structure of these tiny airborne droplets and what that means for predictions around air quality, pollution spread, and climate models.
Yangyang Liu, a research scientist in civil and environmental engineering, and Peter Vikesland, the Pryor Professor of Engineering, found in lab studies that these particles have an outer “shell.” Inside the droplet, the chemistry may be acidic, but the outer surface can become strongly alkaline because fatty compounds, similar to oils released during cooking, form a coating around the particle. That coating creates tiny electric fields that change the chemistry at the surface and may play a major role in how pollution particles change after they’re released into the air.
“Most people imagine a droplet as being the same all the way through, like a drop of water,” Liu said. “But we discovered that these airborne particles behave more like an M&M candy. The inside and the outside have a very different chemistry.”
Their findings were recently published in Proceedings of the National Academy of Sciences.
Why does it matter?
Most important pollution reactions happen on the outside of these particles, where they touch the air. If the surface behaves differently than the inside, the particle can change much faster than scientists have historically expected, according to the research.
For people, this affects several important things:
- What humans breathe: Cooking smoke, wildfire smoke, and urban pollution may transform in the air differently than expected, which can influence air quality and health.
- How pollution travels: These particles can change chemically as they move through the atmosphere, affecting how long pollution stays in the air and how far it spreads.
- How weather is predicted: Tiny airborne particles help form clouds and influence how sunlight moves through the atmosphere, meaning the new research could affect weather and climate models.
- How pollution is predicted: Scientists use computer models to predict pollution and its health impacts. If particle surfaces behave differently from their interiors, those models may need updating to better reflect reality.
Recreating atmospheric chemistry in a lab
Vikesland and Liu relied on controlled laboratory simulations rather than collecting air samples directly from the field. By generating tiny aerosol droplets coated with fatty acids, they were able to study the chemistry happening at the droplet surface. These controlled simulations allowed them to measure extremely small electric fields and observe complex reactions, including the formation of a highly alkaline outer shell around the droplets.
These findings challenge the long-held view of airborne particles as chemically uniform droplets and point to a more dynamic picture of how they evolve in the atmosphere. By revealing how much activity is on particle surface, the research provides new insight into how pollution changes once released into the air and underscores the need to better account for these processes in future air quality and climate models.
Journal
Proceedings of the National Academy of Sciences
Article Title
Interfacial electric fields create hyperalkaline shells on fatty acid–coated microdroplet aerosols
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