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Air Quality in Transit Buses (2023) / Chapter Skim
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Day 1 Session 1
Pages 5-15

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From page 5...
... (current) , Moderator Presenters Meghan Ramsey, Massachusetts Institute of Technology Lincoln Laboratory William Lindsley, National Institute for Occupational Safety and Health; Centers for Disease Control and Prevention Donald Milton, University of Maryland William Lindsley and Meghan Ramsey laid the foundational knowledge of the science of disease transmission and air quality and the biological threats to the public.
From page 6...
... The highest concentrations are closest to the source, and that concentration falls off farther away from the person. Air currents and ventilation systems have a big effect and can sweep aerosols toward people or away from people, and they can also take aerosols out of a confined space.
From page 7...
... The infectious dose of other viruses can be much higher. The infectious dose also depends on where in the respiratory tract the virus deposits.
From page 8...
... Similar to the challenges and potential health and economic impacts that traditional biodefense or biothreat agents pose, naturally occurring diseases also pose an enormous threat. Both traditional biothreat agents and naturally occurring diseases are of increasing concern because of the reduced barriers to gaining access to these biothreat agents.
From page 9...
... For a respiratory disease such as COVID-19, the respiratory aerosols that are produced may contain virus, and studies have shown viral particles can be present in these smaller respiratory aerosols that get produced. A significant portion of these small particles can contain virus and, because they remain airborne for longer, are of particular concern.
From page 10...
... A higher ACH, or a higher number of ACH, means more air exchange and generally lower risk for breathing in infectious aerosols that might be in the environment. One way of measuring ACH for a particular environment is by using a tracer gas such as sulfur hexafluoride to get a quantitative measure of the impact of changing operating conditions.
From page 11...
... The challenge with tracer gases is that they do not capture all the complexity of respiratory aerosols because they will not settle onto surfaces as particles do and they cannot be removed by filtration. Ramsey explained that more complex simulant materials can be designed to mimic the properties of respiratory aerosols to help researchers understand how those aerosols move through vehicles.
From page 12...
... Milton further described research that cultured the COVID-19 virus from both particles of less than 5 microns and larger than 5 microns; the fine particles penetrated filters the most and traveled the farthest. Milton also noted that on a crowded bus, direct UV air sanitation with 222nanometer UV is a useful technology for sanitizing air at that short range, but how much UV is needed and how to best design a deployment to make it the most effective are challenging issues.
From page 13...
... For example, a barrier is a great defense against a squirt gun, but cigarette smoke has small aerosols that can go around the barrier, and that barrier can stop the airflow and cause the cigarette smoke to build up. In response to an audience question on how the pandemic circumstances can lead to supporting the development of new technologies to improve air quality inside transit buses, Lindsley and Ramsey agreed that the pandemic has been a learning experience on filtration, ventilation, and air disinfection, and that these biothreats are not going away.
From page 14...
... has provided an engineering controls summary of attempted technologies titled "Layered Approach to Reducing the Impacts of COVID-19 on Transportation," available at https://www.vtti.vt.edu/covid-engrg-controls/. VTTI has also published a summary of external air impacts and use of existing air handling features on transit bus airflow, available at https://www.vtti.vt.edu/PDFs/Transit%20Bus%20Engineering%20Controls.pdf.
From page 15...
... Concentration of MS2 at each sampling time point during tests of an antimicrobial air treatment product. The product was dispersed in a test chamber at an EPA specialized Aerosol Test Facility in Research Triangle Park, North Carolina, prior to MS2 aerosolization.


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