allotments
Member
I recently bought a portable PM2.5 monitor to measure that component of air quality. PM2.5 being fine particulate matter, particles that are 2.5 microns or less in diameter.
The device is consistently returning readings compatible with readings from more expensive devices. It's sensitive to small changes in air quality and I've found no reason to doubt the readings.
I was very pleasantly surprised to find that PM2.5 measured in newer trains is lower than external air. I hadn't previously realised this.
An example on Elizabeth Line underground from Farringdon to Liverpool Street: Air on the platform was PM2.5 = 10µg/m3. Inside the train with doors open PM2.5 was the same 10µg/m3 but after doors closed on departure the PM2.5 readings dropped quickly and steadily to 5µg/m3. On arrival at Liverpool Street doors open PM2.5 climbs immediately to 10µg/m3.
This pattern is repeated at and between each station stop. Not only on Elizabeth Line, but on above ground Thameslink, Greater Anglia and London Northwestern trains. Even the newer Transport for Wales class 197 diesel trains do this. All of the trains quickly reduced PM2.5 soon after doors closed. I think this also suggests that all the air in a train is reprocessed by air conditioning systems within a minute or so.
For older diesel trains not so good. On a class 158 accelerating after idling for 10 minutes the PM2.5 level climbed from 6 to 20. An Avanti Voyager at station pushed slightly cleaner air into the door vestibule 14µg/m3 than outside 20µg/m3 with notably cleaner air obtained by closing train door, but when using diesel power between stations values went back up to 20 then dropped before arriving at next station stop.
I found in a typical modern VW car the PM2.5 value was the same as air outside. This presents a marketing opportunity for the railway: Passengers breathe in cleaner air in trains than travelling by alternative modes of transport. It's also very good news for rail staff who spend long hours on trains.
It seems that air conditioning on modern trains is filtering out about half the PM2.5 even when outside air PM2.5 is low. There is some impressive design and maintenance going on!
I would be interested to know more about the specification for air conditioning and filtering and associated maintenance on trains, if Rail forums members could enlighten me.
The device is consistently returning readings compatible with readings from more expensive devices. It's sensitive to small changes in air quality and I've found no reason to doubt the readings.
I was very pleasantly surprised to find that PM2.5 measured in newer trains is lower than external air. I hadn't previously realised this.
An example on Elizabeth Line underground from Farringdon to Liverpool Street: Air on the platform was PM2.5 = 10µg/m3. Inside the train with doors open PM2.5 was the same 10µg/m3 but after doors closed on departure the PM2.5 readings dropped quickly and steadily to 5µg/m3. On arrival at Liverpool Street doors open PM2.5 climbs immediately to 10µg/m3.
This pattern is repeated at and between each station stop. Not only on Elizabeth Line, but on above ground Thameslink, Greater Anglia and London Northwestern trains. Even the newer Transport for Wales class 197 diesel trains do this. All of the trains quickly reduced PM2.5 soon after doors closed. I think this also suggests that all the air in a train is reprocessed by air conditioning systems within a minute or so.
For older diesel trains not so good. On a class 158 accelerating after idling for 10 minutes the PM2.5 level climbed from 6 to 20. An Avanti Voyager at station pushed slightly cleaner air into the door vestibule 14µg/m3 than outside 20µg/m3 with notably cleaner air obtained by closing train door, but when using diesel power between stations values went back up to 20 then dropped before arriving at next station stop.
I found in a typical modern VW car the PM2.5 value was the same as air outside. This presents a marketing opportunity for the railway: Passengers breathe in cleaner air in trains than travelling by alternative modes of transport. It's also very good news for rail staff who spend long hours on trains.
It seems that air conditioning on modern trains is filtering out about half the PM2.5 even when outside air PM2.5 is low. There is some impressive design and maintenance going on!
I would be interested to know more about the specification for air conditioning and filtering and associated maintenance on trains, if Rail forums members could enlighten me.