A growing body of research has made it clear that airborne transmission of the coronavirus is possible.

Why it matters: That fact means indoor spaces can become hot spots. Those spaces also happen to be where most business and schooling takes place, so any hope for a return to normality will require better ways of filtering indoor air.

What's happening: After a concerted campaign by scientists, the WHO last month updated its guidelines on COVID-19 to include the possibility that the coronavirus could be airborne.

• That marked a shift from initial assumptions that the virus was mostly transmitted via contaminated surfaces and respiratory droplets emitted at close range, like an infected person coughing near someone susceptible.
• More evidence was added to the airborne hypothesis last week, when researchers at the University of Nebraska Medical Center reported in a paper published in Nature that they had found coronavirus-filled aerosols — small airborne particles of fluid — in the air of COVID-19 patients' hospital rooms.
• It's still not clear just how much or how often the airborne transmission happens, a question Anthony Fauci has said the White House coronavirus task force will examine.

Context: If coronavirus-contaminated aerosols can indeed hang in the air, perhaps for hours, then "mitigating airborne transmission should be at the front of our disease-control strategies for COVID-19," Joseph Allen of Harvard's Healthy Building program wrote in the Washington Post.

• Schools in particular "definitely present a challenge," says Barry Po, president of connected solutions for mCloud Technologies, a provider of cloud-based remote HVAC management. Many school buildings in the U.S. are old and poorly ventilated, which makes them prime locations for indoor transmission.

The good news is there are existing technologies that can filter out or destroy coronavirus trapped in indoor air.

• The easiest way is simply opening windows whenever possible, which dilutes the amount of virus in the air. In Japan windows are kept open in subway trains, which has helped prevent outbreaks in the country's crowded transit system.
• Portable HEPA filters, which can cost as little as a few hundred dollars, are capable of capturing particles as small as the novel coronavirus and could be used to clean individual classrooms.
• Commercial HVAC systems can be adjusted to increase the number of times they exchange air per hour, analysts from McKinsey said in a report last month.

The catch: Increasing ventilation decreases energy efficiency, and Po estimates that net energy costs for buildings could increase by at least 10% in the COVID-19 era.

A more high-tech solution involves the use of specialized UV light to deactivate coronavirus in the air or on surfaces.

• Fred Maxik, the founder of Healthe Lighting, developed Far UVC 222, a short-wave UV light spectrum that the company reports can neutralize 99.9% of coronavirus in a space. The UV light breaks the chemical bonds in the virus, Maxik says, making it incapable of replicating.
• Unlike the UVB rays in sunlight that can damage DNA and cause skin cancer, Far UVC 222 doesn't penetrate the human body.
• The Healthe system has been installed in Seattle's reopening Space Needle, as well as the practice facilities of the Miami Dolphins. "This is one of the only methodologies where we can continually clean a space in real time," says Maxik.

The bottom line: Despite the runs early in the pandemic on Clorox wipes, it may be the air we breathe more than the surfaces we touch that need to be kept clean.