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Norcross: A meteorological perspective on coronavirus and air freshener

The latest advice to stop coronavirus spread: Keep the air moving. Weather expert Bryan Norcross explains what he means.
The latest advice to stop coronavirus spread: Keep the air moving. Weather expert Bryan Norcross explains what he means. (Image via Openclipart)

MIAMI BEACH, Fla. – I don’t know much about viruses, but I do know a little about air. As time has gone on, it’s become clear that large numbers of people are getting sick because the coronavirus is moving from an infected person to nearby people through the air. 

When was the last time you saw somebody cough or sneeze in public so virus could spread across countertops or doorknobs? And when was the last time you stuck your finger in your eye, nose, or mouth? That’s not happening, so that can’t be how all these people are getting infected. It could still happen, of course, but the odds are low, to say the least.  

So let’s think about the air. 

Spray some air freshener in an average-sized living room. It lingers. You can smell it for minutes, tens of minutes, or longer.  That’s the idea. You usually want to cover up another smell you don’t like. An air freshener that fades fast defeats the idea. 

Now spray the same air freshener outside. What happens? The smell is gone in no time. There’s something fundamentally different about outside and inside the house.

The short answer is, the air outside is moving. The space is bigger, too, of course. But the key point is, droplets of all sizes are dispersed by natural air currents, which are almost always present.

When there is a breeze, none of this is a surprise.  But even then, the actual airflow on a breezy day is much more complicated than it seems. The moving air runs into buildings, trees, cars, people, the ground, and everything else. Some places the air goes fast, some places it’s blocked and makes a swirl. All kinds of random deflections happen due to the moving air’s interaction with the earth and things on it. 

So even with a light breeze, the air is in fact turbulent. At any one point, a hunk of air could be moving left, right, up, down, forward, or back. So the air freshener, or any aerosol or airborne droplets — like somebody’s breath or cough — gets dispersed. Different parts of the cloud get carried away in different directions, and the concentration of the smell or the virus decreases rapidly.

Even when there is no breeze, there is almost always turbulence in the air outside.  During the day, it’s obvious.  The sun heats dark objects more than light ones. Air rises fast off of dark colors and less so off light. It’s cooler under the trees, and over the grass.  All these natural temperature differences make the air swirl and lift and fall in ways we don’t detect.  So even on a day when the air seems still, the air freshener will still disperse outside.

In addition, of course, the ultra-violet light coming from the sun is a great disinfectant. So interaction with another person on a sunny day is automatically safer.

When we’re inside, none of the natural turbulence-causing factors exist, so our spritz of air freshener sticks around. 

So what can we do?

First, we can open the window. A breeze blowing through the house is good for obvious reasons, but it’s not always practical in the summer. The easy alternative is to turn on a fan. Blow the air around. Create turbulence.

This doesn’t take the airborne particles out of the room, but it spreads them out. It breaks up the cloud. You can prove it with air freshener. The smell goes away much faster. 

And that takes advantage of a key point the epidemiologists make: The more virus you breathe in, the more likely you are to get infected, and perhaps the worse the infection will be. 

If you disperse the cloud, and send the virus up to the ceiling, down to the floor, and all over the room, you significantly lower the chance of anybody breathing in enough virus to get sick.

It doesn’t even have to be a big fan. Just move the air.

The bottom line: Outdoors will always be better than inside.  And keeping your distance and wearing face coverings are still the first lines of defense when you’re around people.

But when you’re inside with your family and presumably safe, turn on a fan in the room. 

If somebody has the virus and doesn’t know it, every time they speak, they are emitting some virus. And if they shout or sing, they emit more. If you disperse it from the get-go, you lower the chance that anybody else will breathe in enough to get infected.  t’s an odds game. 

So I’m adding a COVID rule from a meteorological point of view: Get tested, wear a mask, keep your distance, wash your hands, and keep the air moving.


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