COVID-19 may float in the air. This is what it could mean. | States and Regions

RALEIGH — “How big is it?” Frequently asked questions when explaining something new. However, this is also a crucial and controversial part in understanding the spread of COVID-19.

The size of coronavirus is well known to scientists. At 100 nanometers, 200 virions, which represent a single particle of the virus, can fit within the width of the finest human hair. But the virus needs to be carried by something.

Coronaviruses generally hide the water droplets released when a person exhales. And the size of the droplets that can carry virions may mean the difference between returning safely to school or office and another round of telework or homeschooling.

Scientists do not agree on how large these droplets must be.

The discussion went public last week when more than 200 scientists published open letters to health organizations around the world. Signers argued that there is new evidence that COVID-19 could be an airborne infection carried by the smallest droplets. A few days later, the World Health Organization issued a slightly revised guidance to address this possibility.

Glenn Morrison, one of the 239 scientists who teaches environmental science and engineering at UNC-Chapel Hill, said: I signed the letter. “It’s the assumption that you can go anywhere.”

With the exception of certain medical settings, the current guidelines of most public health organizations are designed to protect people from the large droplets that carry coronaviruses. They tend to fall to the ground quickly within a few feet of their source. This is why people are encouraged to stay 6 feet apart in public places.

However, “microdroplets” or “droplet nuclei” of less than 5 microns can remain in the air as aerosols, which can be suspended for several hours and hung and travel long distances.

When people exhale, they emit droplets of any size, whether coughing or regular breathing. Barbara Turpin, also chair of the UNC’s Environmental Sciences and Engineering Department, who also signed the letter, said that someone infected with COVID-19 could produce about 600 drops containing coronavirus per minute.

“There is a rational scientific debate about how COVID-19 is spreading,” Turpin said. The controversy is the relative importance of droplet transmission compared to airborne transmission by aerosol, based on what size virus can be retained.

According to Morrison, scientists do not have enough knowledge to prove that airborne infections are so rare that they can be ignored. Studies looking back at the SARS epidemic caused by closely related viruses have shown that the disease was transmitted in the air.

Jim Chan, chairman of the ecotoxicology and environmental health program at Duke’s Nicholas Environmental School, points out that scientists’ letters do not claim that current precautions are not important. “We haven’t challenged these to be right, such as washing our hands and putting on face masks that cover the face and nose.”

A concern is that increasing the concentration of virus-containing aerosols in poorly ventilated indoor environments does not allow the current recommendations to adequately protect the population. This is especially important as companies and schools are considering reopening.

Imagine, in a classroom or bar, infected people being quarantined and healthy people on the other side, according to Tarpin. Droplet-borne viruses cannot be transmitted by healthy people at a distance. However, airborne viruses can travel farther, and the probability of infection increases as everyone spends more time in the room, exhaling more virus into the air.

The three experts agreed that the most important way to reduce the spread of airborne viruses was to reduce the concentration of the virus in the air by adequate ventilation. One way to do this is to move more interactions out. “Any activity you can do indoors is always safer outdoors,” Turpin said.

Zhang likens it to smoking. “That’s why we asked people to smoke outside. Smoking one cigarette is the same amount of content.” Outdoors, smoke and pollutants quickly dilute.

Buildings should also strive to increase the amount of outside air that can be taken in through the HVAC system. However, this can be limited by your infrastructure. Intake of fresh air requires more energy to heat or cool than to recirculate the air, and older systems may not be able to increase intake.

Zhang claims that if the system can take in more air, it’s worth the cost compared to the cost of allowing the spread of the coronavirus.

Unfortunately, it can be difficult for the average person to determine if a building or room has good ventilation. Just because the air is moving does not mean it is fresh. In fact, the COVID-19 cluster caused by aerial spraying in restaurants was thought to be due to the severe air conditioning spraying and the spread of coronavirus between the tables.

One of the relatively accessible ways to measure ventilation is to get a carbon dioxide monitor. This can be measured indirectly, Morrison said. If the carbon dioxide concentration exceeds 1 part per million, the space is probably not well ventilated for the internal population.

It may sound counter-intuitive, but if aerosols are spreading, it may be even more important to keep wearing a face mask. This is because many small droplets first come out of a person’s mouth or nose as large droplets. Larger droplets become smaller as the water evaporates and become smaller as they stay in the air.

The biggest takeaway from the scientist’s letter is that we still have a lot to learn about COVID-19.

“People see what science is doing. It’s normal for scientists to have health disagreements about how things work,” Turpin said. “Over time, you will understand it.”