Methylobacteria Propagating Inside Fog Metabolize and Neutralize Formaldehyde from Smog

 

     Researchers at Arizona State University discovered that bacteria propagating and thriving inside fog droplets break down formaldehyde, a toxic pollutant linked to smog and respiratory problems, at rates up to 200 times faster than bacteria in cloud water. Thus, one might say that fog cleans the air of formaldehyde. The study was published in the journal mBio. Researchers observed 32 fog events across two years in central Pennsylvania and revealed that fog droplets are teeming with bacterial life. According to Gadget Review:

“Post-fog air showed 45% higher bacterial counts, with researchers observing enlarged, dividing cells-clear evidence of reproduction inside the droplets. Lead researcher Thi Thuong Thuong Cao noted, “We observed them getting bigger and they’re dividing,” confirming fog as an active breeding ground rather than passive transport medium.”

“Methylobacterium, distinctive pink-pigmented bacteria, comprised nearly one-third of all fog microbes-far exceeding their presence in surrounding dry air. “When you take all of the droplets together, the concentration of bacteria is the same as in the ocean,” explained ASU’s Ferran Garcia-Pichel. These microbes specialize in detoxifying formaldehyde, achieving 95% biological breakdown through metabolic processes that neutralize rather than simply consume the pollutant.”

     The research also shows that there is a strong biological component to some atmospheric chemistry processes. The research also upends atmospheric modeling and must now be taken into account. Another implication of the study involves so-called fog-harvesting, where communities use fog nets for water collection in arid regions. When they do so, they are disrupting the bacteria’s work in breaking down formaldehyde. Methylobacterium is mostly harmless butsome strains pose some infection risks for immunocompromised individuals. The levels of bacteria found in fog were found to be very similar to the levels found in seawater, even though only 1% of the fog droplets contain bacteria.

     The authors noted that fog and its effects on the atmosphere have not been studied enough. More study is needed on the bacterial composition of fogs. Fog effectively becomes a habitat for bacteria. It is difficult to study fog since measurements are needed before, during, and after the fog develops and fades. The presence of wind makes that very difficult. Thus, the research here focused on “radiation fog, which forms on still, calm nights when the ground cools and the air just above it cools with it, until moisture condenses close to the surface.”

     According to earth.com:

“The bacteria were clearing the formaldehyde so fast, though, that simple eating didn’t fully explain it.”

“The team found that at high concentrations, formaldehyde becomes toxic to the bacteria themselves, so they break it down into carbon dioxide to keep their environment safe.”

“The bacteria are not just consuming a pollutant. They’re detoxifying the air as an act of self-preservation and in doing so, making it cleaner for everyone else too.”

     According to Phys.org:

"It's relatively new that people are starting to look at biological activities in clouds, so there's still a lot which we don't understand," adds Pierre Herckes, a co-author and professor in the School of Molecular Sciences. "At nighttime, for example, there isn't that much atmospheric chemistry going on. Chemistry is largely driven by the sun and by light. But if the bacteria are still doing their thing even during the nighttime, they can be important."

     Below, the paper explains why the detoxifying reaction mechanism for self-preservation makes up the bulk of the utilization of formaldehyde by the methylbacteria. The authors also consider that other volatile organic compounds could be utilized by bacteria as well, indicating an area for further study.

“Multiple lines of evidence, including increases in the aerobiome size with intervening fog events, its dependence on temperature, the presence of larger cells, and the high frequency of dividing cells, all speak for a fog water microbiome that is also capable of growth in nebula. While one could find alternative explanations for each of these phenomena separately, in situ growth remains the most parsimonious explanation for all concurrently. That the conditions for heterotrophic activity based on C1 compounds like formaldehyde that are available in the air lead to exceptionally high biodegradation rates in the fog water microbiome is consistent with that notion. However, only a fraction of the formaldehyde processed could be used directly for growth, and most of the activity must serve as a detoxification mechanism.”

References:

 

Scientists are stunned: Your local fog bank is eating toxic chemicals at "impossible" speeds. Nikshep Myle. Gadget Review. May 13, 2026. Scientists are stunned: Your local fog bank is eating toxic chemicals at "impossible" speeds

Fog is teeming with bacteria that eat pollutants and clean the air you breathe. India Today. May 17, 2026. Fog is teeming with bacteria that eat pollutants and clean the air you breathe - India Today

Growth and formaldehyde degradation of photoheterotrophic Methylobacterium within radiation fogs. Thi Thuong Thuong Cao, Pierre Herckes, Derek Straub, Soumyadev Sarkar, and Ferran Garcia-Pichel. Environmental Microbiology. Research Article. 11 May 2026. Growth and formaldehyde degradation of photoheterotrophic Methylobacterium within radiation fogs | mBio

The fog is alive: Droplets host bacteria that clear toxins from our air. Arizona State University. Phys.org. edited by Stephanie Baum, reviewed by Robert Egan. May 12, 2026. The fog is alive: Droplets host bacteria that clear toxins from our air

Fog is alive and quietly cleaning pollution from the air. Andrei Ionescu. Earth.com May 13, 2026. Fog is alive and quietly cleaning pollution from the air - Earth.com