Every time we cough or sneeze, we spew a whole slew of aerosols into the air. Some are big enough that you can see them ejected out of someone’s mouth or nose. Some are “big” in an aerosol physics sense but still invisible to the naked eye, and those settle onto surfaces rather quickly. And some are small enough that they can float around in the air.
What you might not know, though, is that this isn’t happening only when you cough or sneeze. You also release aerosols when you’re just talking and even when you’re just breathing normally.
That presents a particular problem for this virus for three reasons:
►Many, if not most, who get it are asymptomatic so have no idea they have it.
►People can shed a high viral load from their throat before they have symptoms.
►There is evidence that this asymptomatic transmission is happening, a lot.
Outdoors, the shedding of virus during normal talking is not much of a problem, because we can social distance, and the wind dilutes airborne virus quickly.
Even indoors, the average bedroom has a volume of about 1,000 cubic feet of air. This volume of space, combined with a typical home that has an air exchange rate of about 0.5 air changes per hour (meaning half the air in the house is changed with outdoor air every hour), can help dilute the virus.
But what about inside our cars?
The typical family car interior has a volume of about 100 cubic feet, a 10th the size of a bedroom. And we might cram four, or sometimes five, people into that small space. It’s impossible to social distance.
Here’s the potential problem as it relates to COVID-19. Over the decades, we’ve done a really nice job of sealing up our cars. Ever notice how quiet they are on the inside these days? That’s because every effort has been made to seal up every gap possible so there are better acoustics. The result is that the ventilation rate — how much fresh air comes into the car — can be quite low.
This one little change reduces risk
To show what this means for COVID-19 and to give you a simple step to protect yourself and others while in a car, we modeled a simple scenario: riding in car for 80 minutes with an infected passenger who seems fine other than coughing every few minutes.
When the windows are closed, SARS-CoV-2 (in fine aerosol particles) accumulates in the car cabin. With each new cough, the concentration builds up with no significant dilution happening. But even cracking one window open just 3 inches can keep this at bay.
So the next time you’re in the car — be it your own vehicle with others or in a taxi, Uber or Lyft — it’s all the same advice: Open up the windows just a bit, even if everyone is feeling fine.
If you’re using your air conditioning or heat and want to keep the windows closed, make sure the car is not in recirculating air mode — select the mode that brings in fresh outdoor air. Having everyone in the car wear a mask can also help and is a must in a taxi or ride-share vehicle.
Lastly, bringing in more outdoor air only addresses airborne transmission. There are many high contact surfaces inside a car for droplets to land on, so wash your hands after your trip.