Researchers at Arizona State University have discovered that fog is far more alive than it appears, finding that bacteria living inside tiny fog droplets are not only surviving, they are actively growing and helping remove harmful pollutants from the air.
The findings challenge the long-held idea that fog is simply condensed water floating near the ground. Instead, scientists say fog may act as a temporary ecosystem filled with microscopic organisms carrying out important chemical work.
Thi Thuong Thuong Cao, the study’s lead author said: ‘There’s very limited knowledge about what kinds of bacteria are present in fogs, which are like clouds at the ground level.’
Cao and her colleagues wanted to answer two questions: what bacteria exist in fog, and whether those microbes are active inside the droplets.
Ferran Garcia-Pichel, co-author of the study explained: ‘If they are growing, then the droplets are a habitat. That’s a mindset change.’
The team discovered that fewer than 1% of fog droplets actually contain bacteria. Yet because fog contains enormous numbers of droplets, the total amount of microbial life is surprisingly high.
Garcia-Pichel: ‘When you take all of the droplets together, the concentration of bacteria is the same as in the ocean,” “A thimble’s worth of fog water has some 10 million bacteria.’
One type of bacteria, called methylobacteria, drew particular attention. The researchers noticed these microbes became more common during fog events. Laboratory tests showed the bacteria were feeding on formaldehyde, a toxic chemical pollutant linked to ozone smog and health problems.
Cao said: ‘We observed them under the microscope to see that, yes, the bacteria are getting bigger and they’re dividing, so there is growth. We also found that they’re using the formaldehyde as food to support their growth.’
The bacteria appeared to break down formaldehyde so quickly that researchers believe they were not just consuming it for energy, but also detoxifying their environment to protect themselves.
The study focused on ‘radiation fog,’ a type of fog that forms close to the ground in calm, humid conditions overnight. This allowed scientists to track the same air mass before, during and after fog formed.
The team believe their discovery could have practical implications. Some regions are exploring fog harvesting as a possible source of drinking water, especially in dry climates. But the presence of active bacteria means fog water may need treatment before it is considered safe to drink.
Garcia-Pichel said: ‘If we harvest fog, we are getting rid of our little friends in the air. We don’t know if that’s going to make a big impact or not, but we should be considering that.’
The findings may also affect climate and weather research. Scientists increasingly suspect that bacteria in clouds and fog could influence atmospheric chemistry in ways that are not yet fully understood.
Co-author Pierre Herckes, a professor in ASU’s School of Molecular Sciences, said: ‘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.’
The full research can be read here.
Photo: Rino Adamo
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