The virus that causes COVID-19 is an airborne pathogen, and humans are its primary delivery vehicle. Coughing, sneezing and even just speaking release droplets on the order of 100 microns in size (or 1/100th of a centimeter) into the air. “Your larynx is vibrating as you speak and it acts as a little nebulizer,” says Dr. Christopher Gill, associate professor of global disease at the Boston University School of Public Health. (A nebulizer turns a liquid into a mist.)
The half-life of the aerosol droplets is about an hour, according to Gill, which is short, but still leaves plenty of time after which the fluids released by an infected person’s cough or sneeze are infectious. It’s unclear to scientists if a viral particle continues to be infectious when the micro-droplet that contains it evaporates.
Even in a time of social distancing, enclosed public spaces like grocery stores remain problematic, Gill says, since a great many people may pass through an infected space within the hours the virus lingers in the air. “You should worry more about the air you breathe in a grocery store than about whether someone touched the broccoli,” he says.