A Harvard epidemiologist says air conditioning units, especially those in corporate environments, could be contributing to the spread of the coronavirus in the southern part of the nation.Dr. Edward Nardell, who is a professor in the Departments of Environmental Health and Immunology and Infectious Diseases at the Harvard T.H. Chan School of Public Health, says air conditioning can help airborne viruses spread in three ways.The first way is when people go inside to cool down rather than remaining outdoors, where they are safer.The second issue, Dr. Nardell says, is that air conditioning brings in very little outside air.He says that is especially problematic in corporate settings.“It just isn’t economically possible to bring in outside air, recirculate it and dehumidify it,” according to Nardell.Lastly, he explains that when people are indoors, they are typically not spaced out safely, as they would be outdoors. “You are not socially distanced as much, but you’re re-breathing the same air that someone else just exhaled,” Nardell adds. “We call it rebreathed air fraction, and if someone is infectious, often asymptomatic, you’re going to be rebreathing their small particles.”He goes on to say that air conditioning units can also generate air currents that can carry large particles even further, similar to scenario that researchers found contributed to the spread of the coronavirus in an air-conditioned restaurant in Guangzhou, China, involving three family clusters.This tool on the Department of Homeland Security’s website can be used to estimate how long the virus would be expected to remain stable while airborne.The Centers for Disease Control and Prevention (CDC) is recommending that restaurants increase the distance between tables and improve ventilation.The use of germicidal lamps, has proven effective in protecting against tuberculosis infection and is now being used in some settings to fight COVID-19, Dr. Nardell points out.He says the lamps are set up to shine horizontally, high in the room where sterilization is needed.Air currents, which are stirred in part by warmth from human bodies, circulate up to the ceiling, where the ultraviolet light then kills floating pathogens.