Why did I hear about aerosols in the coronavirus pandemic?

The coronavirus pandemic that spread around the world in 2020 led to a lot of news about aerosols , because they turned out to be a major way in which the virus spreads. Note, however, that these virus-spreading aerosols are fairly different from the aerosols that affect the atmosphere more generally. In particular, the virus-spreading aerosols are generally tiny water droplets, while the atmospheric aerosols are usually small solid particles that can cause pollution and can affect weather and climate.

The virus-spreading aerosols work as follows. When you breathe out (exhale), some of water vapor in your exhaled air can condense to make tiny droplets that are small enough to count as aerosols, which in this case means they can remain suspended in the air for many minutes or hours. If you are infected with a virus, then these aerosol droplets may contain the virus. The virus can thereby infect someone else if the person breathes in these virus-containing aerosol droplets (in some cases, the virus may also enter through the eyes), and the fact that aerosols can stay in the air for hours means that infection can occur even in a room that has been empty for a while.

This explains why face masks are so helpful in stopping transmission of the coronavirus: any good face mask will block a large proportion of the aerosol droplets, and those rated as “N95” face masks will block 95% or more of them. Therefore, if you are infected with the virus, wearing a face mask will help prevent you from spreading it to others. If you are not infected, your face mask will help prevent aerosols from entering your lungs, thereby protecting you.

Note that aerosols entering your mouth, nose, or eyes are not the only way that viruses and other germs can spread. In some cases, they are spread by larger droplets that are expelled when a person coughs or sneezes, which is why it is so important to cover your nose and mouth when you do this. In other cases, you can pick up a virus by touching a person who has it or a surface on which the virus has landed, and then touching your face where it can enter your airways. That is why hand washing is so important: washing with soap and water for 20 seconds has been proven to wash away viruses, so that they go down the drain before you can touch your face and become infected. Disinfecting surfaces can also help.

Of course, neither face masks nor handwashing are foolproof, which is why the very best strategy for avoiding infection is to avoid being around infected people. Sick people should isolate, you should avoid large gatherings if there is a chance that some people may be infected, and if you must be around other people, practice “social distancing” by keeping at least 6 feet apart.