Billions Of Viruses Are Raining Down On Us From The Sky Every Day

Viruses and bacteria circulate in the upper troposphere portion of the atmosphere, and astounding numbers fall down to the Earth's surface every day. MarcelClemens/Shutterstock

The germaphobes are correct: There is microscopic life everywhere. It's even drifting around high in the sky and raining back to the ground in high quantities, according to a study by a collaborative group of scientists from Canada, the US, and Spain.

Their findings, published in the International Society for Microbial Ecology Journal, showed that approximately 800 million viruses may be deposited per square meter of land.


“That's 25 viruses for each person in Canada," said author Curtis Suttle, a University of British Columbia virologist, in a statement.

Microbiologists have been trying for some time to figure out how nearly identical viruses seem to end up on opposite corners of the Earth. We know that bacteria and viruses attach themselves to aerosolized particles, most commonly kicked-up dust from deserts or organic molecules from oceans spray, and hitch a ride along the currents of the global atmospheric circulation system above the planetary boundary layer (PBL) – the variable demarcation line between the lower region of the atmosphere affected by land-and sea-driven weather systems and the calmer portion above that begins at altitudes of 1,000 to 16,000 meters (3,280 to 52,500 feet).

The amount and composition of microbial life distributed through both dry and wet air (i.e. washed out by rain), however, has yet to be fully investigated, particularly in regards to viruses.

To prevent contamination from particles circulating within the PBL, the researchers placed their sample collectors on platforms in the Sierra Nevada mountains of Spain, at sites 2.9 and 3 kilometers (9,500 and 9,840 feet, respectively) above sea level. Deposited material was collected either every week or every other week for two years. In order to trace the origin of the microbes recovered, the authors used a well-established computer model that continuously maps the movement of air masses.


The experiment indicated that a maximum of 7 billion virus particles can fall per day under certain conditions. More viruses are dropped from air masses carrying smaller marine aerosols (<0.7 microns) than terrestrial aerosols, and rain does not appear to affect rates. Conversely, bacterial deposition was higher during days of rain or air movement events carrying larger particulates (>0.7 microns), particularly Saharan dust. The viral deposition rates were 9 to 461 times higher than the range for bacteria.

Because viruses are so much smaller than bacteria, it is not surprising that they can carpool through the air with lighter oceanic and gaseous molecules compared with the heavier earth sediments needed to carry bacteria. Yet the observation is important as it confirms findings from other research suggesting that viral particles can stay aloft in the atmosphere longer and potentially travel farther.

"Roughly 20 years ago we began finding genetically similar viruses occurring in very different environments around the globe," said Suttle. "This preponderance of long-residence viruses traveling the atmosphere likely explains why--it's quite conceivable to have a virus swept up into the atmosphere on one continent and deposited on another."


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  • bacteria,

  • virus,

  • atmosphere,

  • weather,

  • viruses,

  • rain,

  • Earth science,

  • wind,

  • troposphere,

  • aerosol,

  • atmospheric circulation