One reason why measles — a notoriously contagious disease — is so difficult to contain is because its infectious viral particles can linger in the air for up to two hours. Can the coronavirus do the same?

It’s a question health officials appear to be grappling with: On Thursday, the San Francisco Department of Public Health said people must wear masks if they are within 30 feet of someone not in their household, a far greater distance than the widely recommended 6 feet of social distancing. Meanwhile, the Centers for Disease Control and Prevention website reads, “It is unknown how long the air inside a room occupied by someone with confirmed COVID-19 remains potentially infectious.”

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While scientists say it is possible that the coronavirus can drift through the air, many note there’s no evidence these tiny bits of virus are enough to make people sick.

To understand how the virus travels by air, it’s important to know whether it’s hitched a ride on a jumbo jet — or a paper airplane.

“It’s basically a size difference,” said Dr. Ronald Collman, referring to the size of the droplets that contain viral particles. Collman is a professor of medicine in the Division of Pulmonary, Allergy and Critical Care at the University of Pennsylvania’s Perelman School of Medicine.

When a person with COVID-19 coughs or sneezes, they spew relatively large droplets — at least 5 micrometers in diameter — into the air. These droplets are filled with viral particles.

Studies have demonstrated how those globs of saliva and sputum are so big and heavy — compared to other respiratory emissions, that is — that they generally come into contact with another person’s face, or fall to the ground or surfaces, within about a six-foot radius.

The CDC believes those respiratory droplets are responsible for the majority of COVID-19 transmissions.

But some studiesshow viral particles can get stuck in tiny aerosols less than 5 micrometers in diameter. They’re too light to fall to the ground, thus becoming airborne.

This is much like the water vapor you can see in your breath when it’s cold, wafting through the air before slowing dispersing.

The potential for the coronavirus to linger in the air is concerning to scientists who study aerosols. Kimberly Prather, a distinguished professor in atmospheric chemistry at the University of California, San Diego, addressed the possibility in a paper published this week in the journal Science.

“Aerosol transmission of viruses must be acknowledged as a key factor leading to the spread of infectious respiratory diseases,” Prather and her co-authors wrote.

But evidence is lacking that this particular virus is indeed infectious in aerosolized form, Prather told NBC News.

“How long does it live when it’s in the air? We still have a lot of work to do to answer that,” Prather said.

Other experts agreed.

“Just because some viral element is detected does not mean it is infectious,” said Dr. Aditya Shah, an infectious disease fellow at Mayo Clinic in Rochester, Minnesota.

That’s because when it comes to making a person sick, viruses tend to get their strength in numbers.

Any pathogen — including SARS-CoV-2, the type of coronavirus that causes COVID-19 — generally requires larger amounts of particles to become infectious. The smaller the particle, scientists say, the less likely it is to carry enough virus to survive a breezy journey into another person’s body.

“I think it is plausible that there could be some level of aerosol transmission,” Collman said. “But if it occurs, it’s probably not very important or common.”

Still, as evidence grows that people can spread the virus without having any symptoms, doctors overwhelmingly support the use of face masks to reduce the risk for infecting others with emissions of all sizes.

“People who don’t wear face masks think that they’re saying, ‘I’m tough. I’m strong. I’m not afraid of getting COVID,'” Collman said.

“What they’re really saying is, ‘I don’t give a damn about other people.'”

While the CDC recommends wearing face coverings in public places to cut the risk of spreading potentially infectious droplets, a study published Thursday in the journal BMJ Global Health suggests benefits to masking at home.

Researchers in China surveyed 124 families in which at least one person had been diagnosed with COVID-19. Households that were able to isolate the ill family member, as well as use disinfectants, had a lower chance of viral spread.

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What’s more, the study suggested wearing face masks in the home was 79 percent effective in curbing spread of COVID-19 among family members.

“This is the first study to show effectiveness of precautionary mask use, social distancing and regular disinfection in the household,” the study authors wrote.

The research also illustrated the elevated risks of transmitting the virus in close quarters, such as sitting around a dinner table or watching TV together. Still, it appears to be too soon for physicians to recommend wearing masks inside the home routinely.

Dr. Katie Passaretti, medical director for infection prevention at Atrium Health in Charlotte, North Carolina, said it may be reasonable to wear a mask inside the home if one family member is often exposed to members of the public, or perhaps is caring for a vulnerable person.

“What’s the biggest bang for your buck?” Passaretti asked. “It probably makes the most sense to encourage [masks] in households with individuals who are at higher risk for more severe disease,” such as older adults or people who have weakened immune systems.

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Portland’s police headquarters was stormed on Friday night as protesters broke windows and lit a fire in the building.

According to Portland Police officials, the city’s Justice Center was attacked amid a riot against the killing of George Floyd in Minneapolis earlier this week. Five arrests have been made at the time of writing.

The Oregonian said protests took a turn shortly after 11 p.m. local time, when some taking part in the demonstration marched on the Multonomah County Justice Center and attacked an office.

Riot police were later sent into the area to disperse protesters with tear gas and stun grenades, the newspaper reported.

In a statement published on social media in the early hours of Saturday morning, Portland Police said: “Two arrests have been made related to this evenings riot. Another arrest was made around 3:30 p.m. yesterday afternoon related to the demonstration near the Justice Center.

“Details will be provided in a press release when more information becomes available.”

Earlier in the evening, the force also said: “The Justice Center has been attacked and a fire has been lit inside. Portland Fire & Rescue is on scene.”

Portland Police also repeatedly warned people in the city’s downtown district to leave the area, saying the area was unsafe as rioting was taking place.

In an emailed statement, a police spokesperson said the incident was “still an active event.”

“Several windows were broken at the Justice Center and a fire was started inside. The fire was extinguished and the Justice Center is not occupied by protestors,” Portland Police spokesperson Officer Melissa Newhard wrote in a statement emailed to Newsweek. “Throughout the city we have seen property damage, looting, and arsons to buildings and vehicles. A riot has been declared and a dispersal order has been given. Gas has been deployed to disperse the crowd. Five arrests have been made at this time.”

A video posted on YouTube by The Oregonian last night showed protesters smashing windows of the Justice Center, with one demonstrator shouting: “F*** you, you f***ing pig.”

Another video showed further damage being done in the downtown area of Portland, with one protester pictured smashing the window of an unidentified building.

Similar demonstrations have broken out in cities across the nation this week as thousands have protested against the killing of Floyd while in Minneapolis police custody.

A video of the arrest showing one officer with his knee on the unarmed black man’s neck sparked the widespread outrage after going viral on social media and other platforms.

Derek Chauvin, one of the three officers who restrained Floyd on Monday, has been arrested and charged with third-degree murder and second-degree manslaughter, both felonies.