Last Updated on May 11, 2021 by cwl

UPDATE: References have been updated on May 11, 2021…

UPDATE: References have been updated on April 22, 2021…

Some CO2 measurements by Professor of Atmospheric Sciences Clifford F. Mass suggests that viruses potentially exhaled by humans pose an almost zero threat when out of doors. This would tend to imply that the wearing of masks by healthy people while out of doors and engaged in physical activity is unnecessary, not to mention borderline insane.

The study says that human CO2 exhalations are higher than the baseline CO2 levels in the atmosphere, so the levels can be measured and compared against the baseline CO2 levels.

The Professor’s measurements confirmed that human CO2 “plumes” (and associated possible viral loads) were quickly diffused into the outdoor air.

So the bottom line so far:  natural ventilation and mixing in the outside air was effective in diffusing the CO2 emitted by people in an outside park environment, even when there was a high density of people.  And if CO2 enhancement by all the people was undetectable, the same would be true of COVID-19 virus emission by any infected individuals.  Parks appear to be entirely safe locations and masks are not necessary.


The article also references the relatively few studies done on outdoor viral transmission.

Quite honestly, one can only be disappointed in the quality of the “studies”  on outdoor transmission, which is surprising at this point in time.  Importantly, there is no compelling published research that demonstrates significant outdoor transmission.  


To be sure, the probability of the outdoor transmission of viruses is not zero, but the odds of getting in a traffic accident on the way to the trailhead are probably much higher than the odds of contracting COVID from some unmasked jogger on the trail.

We also need to remember that the wearing of masks by healthy people is not a “health neutral” practice; there is a growing body of evidence to suggest that there are adverse effects of mask wearing, especially for prolonged periods of time. (2)

So ditch the mask, go outside, breathe in the fresh air, and visualize a sane, functional society.


(1) Is Outside Air COVID Safe?

(2) Masking: A Careful Review of the Evidence

Outdoor Post-vaccination Masking Is Useless

Norms on Mask Wearing Need to Shift

Is It Time to Eliminate Outdoor Mask Mandates?

Time for Us to Stop Wearing Masks Outside

A Misleading CDC Number