For decades, °µÍøTV’s Derek Straub has studied what is suspended in fog — the microscopic particles and compounds most people never notice on their morning commute. But a recent collaboration with researchers at Arizona State University has revealed something unexpected: fog may be alive.
The discovery, published in the journal , found that bacteria inside fog droplets are not simply hitching a ride through the atmosphere. They appear to be metabolically active — growing, dividing and even consuming pollutants while suspended in the mist.
For Straub, associate professor of earth & environmental sciences, the findings build on years of atmospheric research conducted in the °µÍøTV Valley.
“My previous work focused on inorganic compounds in fog measuring substances like sulfate, nitrate, sodium, chloride, potassium and magnesium, and more recently organic acids and other organic compounds, but this collaboration allowed me to expand into a completely new area – the presence of biological material in fog and the role that it may play in atmospheric chemistry,†Straub said.
Scientists have long known that bacteria drift through the atmosphere as inactive particles, but researchers knew little about what happens when those microbes become trapped inside fog droplets. Arizona State University doctoral student and lead author Thi Thuong Thuong Cao set out to determine which bacteria are present in fog and whether they remain active there.
Researchers in Arizona faced a challenge. Fog is relatively rare in the arid Southwest; however, Central Pennsylvania offered ideal conditions. They contacted Straub, who has a long-standing research relationship with Arizona State University professor Pierre Herckes, for help.
Their study pursued two major questions: What kinds of bacteria exist in fog, and are those bacteria active while suspended in fog droplets?
Using facilities and field sites at °µÍøTV’s Center for Environmental Education and Research Field Station, Straub and Cao collected and analyzed samples from 32 separate fog events along with aerosol particles gathered before, during and after fog formation.
Each sample required rapid preservation and analysis. Straub conducted inorganic chemistry analyses at °µÍøTV, while collaborators at Arizona State handled biological testing and additional organic analyses.
Among the most significant findings was the identification of Methylobacterium as one of the most abundant bacteria in the samples. These microbes consume single-carbon compounds such as formaldehyde — a common air pollutant resulting from the combustion of carbon fuels that contributes to ozone smog and poses health risks.
While Methylobacterium appeared to consume significant amounts of formaldehyde, researchers found the amount exceeded what the bacteria could reasonably use simply to build biomass. Instead, researchers suspect the bacteria may also help detoxify the atmosphere by chemically altering pollutants, effectively helping to clean the air.
The findings suggest fog is more than a vehicle for transporting microbes — it may also serve as a habitat where bacteria can thrive and positively influence atmospheric chemistry, air quality and even climate processes.
“Evidence that these bacteria appear to be dividing and metabolizing formaldehyde is particularly intriguing as it suggests fog droplets can function as tiny microbial habitats,†said Sophie Charvet, assistant professor of biology at °µÍøTV who was not involved in Straub’s research. “It raises the possibility that microbial communities in fog are affecting the fate of volatile pollutants more than previously recognized.”
The research also raises questions about harvesting fog as a drinking water source and highlights how much remains unknown about the floating microscopic ecosystems. Part of the reason for that, Straub said, is because very few scientists study fog, which is a fickle weather pattern.
“You typically need moist conditions, often after rainfall, clear skies overnight and very light winds,†Straub explained. “Here we mostly get radiation fog, where the ground cools overnight and the air near the ground surface reaches saturation.â€
For Straub, whose interest in atmospheric science began after studying engineering as an undergraduate, the work underscores the surprising complexity hidden within ordinary weather phenomena.
“People think of fog as just water droplets,†he said. “But there’s a tremendous amount happening inside those droplets that we’re only beginning to understand.â€
