I saw this article on Wired and immediately read it as the topic to me was interesting. I have been using when I lived in Japan in the 1990s and in Singapore in 2010-2o12. I have used the transit system in many other cities including in the US and Europe. And so the topic of air quality in subways (particularly the stations and inside the trains) got my attention. I guess this is not entirely an issue for ground-level and overhead systems like what most of Lines 1, 2 and 3 and the PNR are. Only Line 2 has one underground station (Katipunan Station) and perhaps has that issue. Here is the article about the air in subways:
Baraniuk (April 24, 2023) “The Filthy Truth About Subway Air,” Wired, https://www.wired.com/story/subway-air-health/ [Last accessed: 4/25/2023]
To quote from the article:
“The big unknown is whether all of this particulate matter is actually causing health problems for people. Millions of commuters use metro systems, in many cases for multiple hours a day, five days a week, for years on end. And thousands of transport workers spend even longer in the tunnels. But there are no widespread signs of severe or acute health problems among these populations, even if pollution levels in subways exceed recommended limits. Could there be more subtle, chronic effects, however—impacts on lung, brain, or heart function?”
Indeed, metros or subway systems have been operating for over a century and so far there is limited that we know about the health risks concerning their use by passengers. But this is something to keep in mind as the Philippines builds its first subway line in Metro Manila. The depots and the situation of workers thought may be a different matter. I recall one of my colleagues at the university doing a quick study of the Line 3 depot, which is underground (i.e., underneath the Trinoma Mall), and measurements showed the air quality to be quite bad. Imagine working there and being exposed to that everyday. Those conditions merit further study but require immediate action to improve working conditions considering the impact to health.