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Air Quality in Transit Buses (2023) / Chapter Skim
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Day 2 Session 2
Pages 34-40

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From page 34...
... Mathai discussed the fluid dynamics of airborne disease transmission. Airborne transmission of respiratory pathogens and latent transmission of droplets deal with particle-laden fluid flows.
From page 35...
... Mathai commented that since the pandemic, there has been a lot of interest in the air flow inside a car. A simulation using a reduced order model of the fluid flow inside a passenger car shows that when the rear left window and the front right window are open, the air enters from behind, circulates some inside the cabin, and then finally exits through the front right window.
From page 36...
... Mathai explained that reduced order modeling simulations can be done in a matter of days; however, there are other settings in which reduced order models cannot be used and require solving the full Navier–Stokes equations. For example, in a public setting when people are waiting in a line, people create a cloud of aerosols around themselves, 36
From page 37...
... The warmer air people are breathing out starts rising, so when people walk in these lines, they create fluid mechanical patterns, which creates a multiscale, multidimensional problem. This scenario required a fully resolved simulation that had both space and time dependence, but the velocity patterns that exist around people walking and stopping can be simplified to the shape of a cylinder.
From page 38...
... Jimenez stated that, in considering outbreaks from the literature of established airborne diseases, he found, for example, that TB is not very contagious but that in some cases, the bacterial infection does not cause any symptoms (latent TB) , or the infection begins to cause symptoms within weeks, months, or even years later (active TB)
From page 39...
... For example, a person talking in a room can be modeled and CO2 measured at different distances to measure how much CO2 is exhaled and how much CO2 is reaching a certain distance in front of that person. When cars are closed, they are similar to the close proximity scenario for the dilution factor of exhaled air, meaning they are a relatively risky environment.
From page 40...
... • This is a similar effort from the Boston Public Schools: See https://www.bostonpublicschools.org/Page/8810. A guest commented via chat that using outdoor air for dilution of contaminants is not a viable solution, as the size of HVAC systems would need to greatly increase to heat or cool outdoor air, not to mention that outdoor air along roadways contains higher levels of pollutants than elsewhere.


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