Making music and the flow of aerosols

Members of the Philadelphia Orchestra, including Carol Jantsch, principal tuba player, participated in a study led by Penn scientists Paulo Arratia and Douglas Jerolmack. Their research looked at the aerosols that professional musicians create when they play. Photo credit: Courtesy of Paulo Arratia

The latest research from the labs of Penn scientists Paulo Arratia and Douglas Jerolmack was in response to “a cry for help,” says Arratia.

It was 2020 and the Philadelphia Orchestra, like so many cultural institutions, had suspended performances due to the COVID-19 pandemic. Through PJ Brennan, Chief Medical Officer of the University of Pennsylvania Health System, the orchestra sought expertise to understand if its musicians could resume playing in a safe physical arrangement that would minimize the likelihood of them contracting SARS on each other or their audience expose -CoV-2.

“The orchestra leader didn’t want the musicians to be far apart; they had to be close together to produce the best sound,” says Arratia of the School of Engineering and Applied Science. “But if they had to be separated with Plexiglas, that was also a problem.” The musicians reported problems hearing each other and poor visibility with plexiglass partitions. “The challenge was how do we get away from that until they can play freely but still safely,” says Arratia.

Now in a publication in Physics of Liquids, Arratia, Jerolmack and colleagues report their findings suggesting that the aerosols produced by musicians dissipate within about two meters. The results not only influenced the arrangement of the Philadelphia Orchestra when it resumed performances in the summer of 2020, but also laid the groundwork for how other musical groups might think about safely coming together and playing.

“Having experts like Paulo and Doug who could measure particle size and trajectory and distance and velocity was really valuable in making decisions for the orchestra,” says Brennan, who now serves on the orchestra’s board of directors. “Those decisions included the distance between players, the distancing between sections that had to be masked. When they collated this information along with the testing and case tracking that Penn Medicine conducted, it helped us make decisions with confidence.”

Experimental approach

The research revolved around how many aerosol particles the musicians created, how densely the particles were emitted from the instruments, and how fast they traveled through the air.

“You can let out a large jet of air, but if the aerosol concentration is very low, it doesn’t matter,” says Jerolmack of the School of Arts & Sciences. “Or you can have a lot of aerosols that get concentrated into a narrow jet. These things are important to understand.”

To collect data, the researchers invited orchestral musicians to the campus and brought their wind instruments, including flutes, tuba, clarinets, trumpets, oboes, and bassoons.

In order to visualize and track the aerosols escaping from the instruments as the musicians played, the researchers operated an air humidifier that ejected water vapor droplets from the instruments’ sound funnel. This arrangement was only shifted for the flute player, in which the air humidifier was placed near the musician’s mouth instead of the bell, since air flows over the mouthpiece when playing this instrument.

Researchers then shined a laser beam through the “mist” generated by the humidifier, illuminating the aerosol particles and capturing them with a high-speed camera and particle counter.

“It’s like a rainy day; you can see the water droplets when the sun shines through,” says Arratia.

The musicians played scales continuously for two minutes. Somewhat surprisingly, the researchers found that the wind musicians produced aerosols similar in concentration to those emitted by normal breathing and speaking, with a diameter of about 0.3 to 1 micron.

Particles this size, the researchers say, are small enough to travel far through the air, provided the airflow is strong enough to carry them there. Therefore, measuring their concentration and flow became important in understanding the potential risk that a musician might be passing SARS-CoV-2 to another person.

Assessing flow velocity, the researchers measured velocities of around 0.1 meters per second, orders of magnitude slower than that of a cough or sneeze, which can travel 5 to 10 meters per second. The flute was an outlier, but still only achieved flow velocities of about 0.7 meters per second.

“If you watch the flow, you see these puffs and eddies, and we know they’re spreading, but we didn’t know if there would be anything at all common between these instruments,” says Jerolmack. “Here we found that just by measuring flow and aerosol concentration and count, we can make predictions about how far aerosols will travel.”

The flow of music

Based on their observations, the aerosols produced by these “mini-concerts” dissipated and settled in the flow of background airflow within about 2 meters or 6 feet — reassuringly similar, the researchers say, to what was measured for normal speaking or breathing . Only the aerosols produced by the flute and trombone went beyond that distance, for the flute perhaps because the air flows over the instrument rather than the instrument acting like a mask to prevent the spread of aerosols.

Overall, woodwind instruments emitted slightly lower aerosol concentrations than brass instruments, possibly because the instrument’s wooden elements absorbed some of the moisture and the numerous holes along the instrument may reduce the flow of some aerosols, the researchers speculate.

Because the researchers’ measurements have not been linked to any particular quality of SARS-CoV-2, they can be used to extrapolate how transmission of other respiratory pathogens might be affected by making music.

“Now you have something to work with for potential future problems, maybe a flu outbreak or something like that,” says Arratia. “You can use our insights into the flow, put in your infectivity and viral load numbers and adjust them to understand the risk.

“It wasn’t exactly an issue that we routinely work on, but we felt compelled to address it,” he says. “It’s been a lot of fun, and we’ve been fortunate to work on a problem that has made a meaningful difference during the trying times of the pandemic.”


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More information:
Quentin Brosseau et al, Flow and Aerosol Dispersion of Wind Musical Instruments, Physics of Liquids (2022). DOI: 10.1063/5.0098273

Provided by the University of Pennsylvania

Citation: Music-making and the flow of aerosols (2022, July 14), retrieved July 15, 2022 from https://phys.org/news/2022-07-music-making-aerosols.html

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