Why is outdoors safer than indoors?

Socializing Staying Safe

Q: If I’m outside, do I still have to worry about all the other things like staying 6 ft apart and wearing a mask?

A: As highlighted in this NYT article, there are two main reasons why transmission of SARS-CoV-2 may be lower in outdoor settings compared to indoor settings:

Airflow and Space!

When a person sneezes, coughs, laughs or sings outdoors, increased airflow and space enables any droplets expelled to be more rapidly dispersed into the environment, compared to indoor spaces, especially those that are small and poorly ventilated.

Why does this matter?

While the exact amount of SARS-CoV-2 virus an individual needs to be exposed to, in order to become infected (i.e., the infectious dose) is still being studied and likely varies somewhat from person to person, your likelihood of coming into contact with a quantity of virus sufficient for you to become infected may be lower in outdoor settings because of greater dilution of the virus in the air (think of the amount of cigarette smoke you might inhale if someone was smoking next to you in an elevator vs. next to you at a park).

Is being outside enough?

While we have yet to see a major superspreader event occur in an outdoor setting (see our prior post for more info on this), transmission of COVID-19 is still possible (and most definitely can occur) outdoors. Droplets typically travel 1-2 meters in the air before falling to the ground, so if you are less than 6 ft from others, your chances of encountering enough virus to get sick may still be fairly high even with the added benefit of increased droplet dispersion outdoors. Droplets expelled when yelling or singing may also travel farther or be expelled in higher concentrations into the air, so the benefit of being outdoors and even to 6ft of space from others, may also be lower in this context. In addition, the extent to which you and those around you wear masks, the number of people gathered is large and/or the duration of time people gather is long will also shape the risk of transmission outdoors.
So, while for gatherings with others outside your household, outdoors > indoors, outdoors + 6 ft distance from others is even better, as is outdoors + mask use, and outdoors + 6 ft distance + mask use is even better still, particularly as the group size and/or duration of time people gather increases.

Overall, choosing to engage in outdoor activities and interactions is a great start, but we should still consider how adding on each and any additional SMART practice below, can further reduce risk of transmission, given the situation!

S: SPACE — Keep your distance, 6ft. or more!
M: MASK — Keep it on! #masksforall
A: AIR — Keep it fresh! Outside is best!
R: RESTRICT — Keep it small! Restrict socializing to a small and stable group of friends and family!
T: TIME — Keep it short! Less time together means less chance for virus spread!

Link to original FB post