Viruses can linger for hours in areas with poor ventilation

Scientists from leading research institutions across the United States are urging that experts unite to deliver a clear message to the public about how viruses like COVID-19 spread in the air. In an open letter published in the journal Science, the team emphasizes that the scientific community must clarify the terminology used related to aerosols and droplets.

The letter states that public health officials should make a clear distinction between droplets ejected by coughing or sneezing,  which have inspired the social distancing standard of six feet, and aerosols that can carry the virus over much greater distances. Virus-containing aerosols that are smaller than 100 microns can remain airborne in a confined space for hours at a time. These aerosols also accumulate in poorly ventilated air, leading to virus transmission.

Kimberly Prather is the director of the Center for Aerosol Impacts on Chemistry of the Environment based at Scripps Institution of Oceanography at UC San Diego. Prather, who led the team of experts, said that the attention must be shifted to focus on protecting the public against airborne transmission.

“Viruses in aerosols can remain suspended in air for many seconds to hours, like smoke, and be inhaled,” wrote the experts. “They are highly concentrated near an infected person, so they can infect people most easily in close proximity. But aerosols containing infectious virus can also travel more than [two meters] and accumulate in poorly ventilated indoor air, leading to superspreading events.”

In addition to wearing a mask, social distancing and hygiene efforts, the researchers are urging public health officials to express the importance of moving activities outdoors, using ventilation and filtration to keep indoor air as safe as possible, and improving protection for high risk workers.

“The goal of this letter is to make it clear that the SARS-Cov-2 virus travels in the air and people can become infected via inhalation,” said Prather. “It is important to acknowledge this pathway so efforts can focus on cleaning the air and providing guidance on how to avoid risky indoor settings.”

Co-author Linsey Marr is a professor of Civil and Environmental Engineering at Virginia Tech and an expert on airborne transmission of viruses.

“It is important for people to wear masks at all times in public buildings and confined spaces, not only when we can’t maintain social distance,” said Marr. “This isn’t just an academic question, but a point that will help reduce transmission if public health officials offer clear and forceful guidance about this.”

The letter is published in the journal Science.

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By Chrissy Sexton, Earth.com Staff Writer