Monday, May 27, 2013

How Healthy is the Air in Subways?

Culture-Independent Analysis of Aerosol Microbiology in a Metropolitan Subway System(32 page pdf, Charles E. Robertson, Laura K. Baumgartner, Jonathan K. Harris, Kristen L. Peterson, Mark J. Stevens, Daniel N. Frank, and Norman R. Pace, Appl. Environ. Microbiol., Mar. 29, 2013)

Also discussed here : How Gross Is the Air of the NYC Subway, Really?(Henry Grabar, the Atlantic - Cities, Apr 26, 2013)

Today we review some research into the quality of the air found in subways, not just the physical and chemical content, but also the microbiological properties in a rare glimpse in that direction. Results show that the air quality inside the tunnels closely resembles the outside air quality as a result of a highly efficient exchange of air by the movement of trains themselves called “train-pumping”. The differences that do exist are interesting: more aerosols made up of tiny metal particles generated by the metal wheels and tracks and skin flakes that are emitted by the people using the subways and generated by convection from their skins- but the density found is no worse than in similar gatherings of people in offices for example. Perhaps the most significant aspect of the study is to predefine the conditions of subway air before the possibility of a terror attack using microbiological substances. All of this is important. as more and more cities turn to Light Rail (LRT) to meet their transit needs in addition to those with Heavy Rail.


Key Quotes:

“The goal of this study was to determine the composition and diversity of microorganisms associated with bioaerosols in a heavily trafficked metropolitan subway environment.”

“There are lots and lots of regulations and pieces of information on aerosol chemicals and aerosolized particles in our society.. There’s no assessment of microbiological air quality.”

 “airborne particulate materials in subways are different from what is found on city streets or in other indoor environments. This is particularly due to aerosolized metallic dust, which most likely is generated by the action of iron train wheels on tracks”

 “our survey finds that the microbiota encountered in the NYC subway is fairly mundane, essentially a mix of outdoor air with an overlay of human-associated microorganisms typical of the skin.. this survey provides the pre-event information necessary for surveillance activities for pathogens that might occur or be introduced into the system.”

“The general uniformity of microbial assemblages throughout the system indicates good air mixing, a testimony to the efficiency of the train-pumping process.”
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