PM2.5 is lower than outside air in newer trains

[allotments]

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.

 

[dk1]

Thank you but this might as well be in Chinese for all that I understand or have knowledge of it.

 

[Nova1]

Thank you but this might as well be in Chinese for all that I understand or have knowledge of it.

Basically
Air is being filtered inside trains

 

[Nunners]

Very interesting. Was the PM2.5 level on the Elizabeth line and Thameslink platforms higher than the air outside, in London? I appreciate this will depend a lot on how far you are from a road

 

[dk1]

Basically
Air is being filtered inside trains

Isn’t that good? I’m laughing as to why it matters or am I missing something?

 

[SynthD]

Isn’t that good? I’m laughing as to why it matters or am I missing something?

Dust and soot particles in the air will settle. You want them to settle in a filter, not as dirt and grime on surfaces you can see, or in your lungs.

 

[allotments]

Very interesting. Was the PM2.5 level on the Elizabeth line and Thameslink platforms higher than the air outside, in London? I appreciate this will depend a lot on how far you are from a road

Elizabeth Line underground on platform was 10 while above ground was 5

Thameslink sampled elsewhere above ground not in the core at Farringdon

 

[dk1]

Dust and soot particles in the air will settle. You want them to settle in a filter, not as dirt and grime on surfaces you can see, or in your lungs.

Thank you. I’ll just take your word for that. I’m none the wiser really. Everything seems fabulously cleaner than I remember it when starting my career in the 80s.

 

[allotments]

Dust and soot particles in the air will settle. You want them to settle in a filter, not as dirt and grime on surfaces you can see, or in your lungs.

I think PM2.5 particles are small enough to remain airborne without settling as dust

 

[mikeb42]

Isn’t that good? I’m laughing as to why it matters or am I missing something?

If you'd prefer to postpone expiring from a heart attack, cancer or many other morbidities then the answer is - yep. For details, see: lots of complex science.

That said, exactly *how* good is a less settled matter.

You make a good point that if (like me and you I suspect ) you've been around a while it may be a bit like the health benefits of laying off that whisky chaser but only after your 17th pint of the day...

Exhaust gases seemed to be the inhalation of choice on the generation of diesel trains that have now passed into history. There was probably more nutrition in the "air" than the BR sandwich of blessed memory.

That said it probably wasn't PM2.5 which is more insidious because the particles (2.5 nanometers) are so tiny that the contention is that they can pass directly into your bloodstream. Those old diesels mostly produced particles so big you could feel them hitting you in the face!

More generally:

i) IETs on diesel stink in the passenger compartment. I'd like to know (or maybe not) what's in that lot.

ii) In the VW Golf example above, was that with the aircon on and on recirculate? It should/could have HEPA filters and the like in circuit just like a train with much the same result unless there's other considerations.

 

[snowball]

About 30 years ago there was more worry about PM10s than PM2.5s. Maybe that was because they had no equipment that could detect PM2.5s?

 

[DynamicSpirit]

Elizabeth Line underground on platform was 10 while above ground was 5

I'd be interested to know how that compares with some of the other underground lines. Certainly, at Tottenham Court Road, interchanging between Elizabeth line and the Northern line, I can practically smell the air becoming dirtier as you get nearer the Northern line platforms, so my guess is they will be massively worse than the Elizabeth line.

That said it probably wasn't PM2.5 which is more insidious because the particles (2.5 nanometers) are so tiny that the contention is that they can pass directly into your bloodstream. Those old diesels mostly produced particles so big you could feel them hitting you in the face!

I would presume that older diesels producing lots of bigger particles doesn't rule out them producing lots of PM2.5 particles too?

 

[mikeb42]

I would presume that older diesels producing lots of bigger particles doesn't rule out them producing lots of PM2.5 particles too?

No expert, but my understanding is that this is more a feature of modern types:

Combustion at much higher pressures

Paradoxical effects of emission control measures like Exhaust Gas Recirculation

Could be a complete misunderstanding though. Google probably knows more and very likely there are people who really know about diesel engines on here!

Meanwhile, IETs still stink of (catalysed) exhaust on diesel - like the one I'm on now. On the face of it, doesn't seem that health enhancing...

 

[Lloyds siding]

Not an expert on A/C but I can make some generalisations.
Yes, some car manufacturers have boasted that their exhaust emissions of particulates are cleaner than the air drawn into the engine. The same will be true for train engines.
Older trains (and buildings) often had badly sited A/C intakes, picking up engine exhaust fumes and particulates.

About 30 years ago there was more worry about PM10s than PM2.5s. Maybe that was because they had no equipment that could detect PM2.5s?

Correct. Instruments for PM2.5s were not widely available.

I'd be interested to know how that compares with some of the other underground lines. Certainly, at Tottenham Court Road, interchanging between Elizabeth line and the Northern line, I can practically smell the air becoming dirtier as you get nearer the Northern line platforms, so my guess is they will be massively worse than the Elizabeth line.



I would presume that older diesels producing lots of bigger particles doesn't rule out them producing lots of PM2.5 particles too?

Yes, they produced lots of PM10s ....and PM2.5s but we only really knew about the PM10s because they were easier and cheaper to measure.
Combustion is a big producer of particulates, whether in engines or fires including bonfires, wildfires, heating appliances, however there are other sources: e.g. brake dust, tyre wear residue, agriculture (watch a combined harvester in action, though dust suppression is now available), forestry, industrial processes, road (and rail) wear and mineral quarrying and processing. In addition there are lots of natural sources: sand and soil blow, plant decomposition, seaspray, volcanoes.
When I was measuring air pollution in recent times our biggest reading was by a main road, but detailed investigation showed that the main source was not traffic on the road, but a busy lorry park nearby, which had a gravel surface, producing lots of PMs when lorries moved.
The Guardian was surprised that Eastbourne was one of the UK's most polluted towns a few years back.
Eastbourne a surprise name in UKs most polluted towns and cities
I'll make an inspired guess that Eastbourne's problems are largely salt particulates from seaspray.

 

[Krokodil]

I would also like to see readings for the deep tube lines. Comparisons between Marylebone and the other London termini too.

 

[allotments]

In the VW Golf example above, was that with the aircon on and on recirculate? It should/could have HEPA filters and the like in circuit just like a train with much the same result unless there's other considerations.

That's a good point. I'll take a close look at the car and report back.

 

[Lloyds siding]

Just swapped the HEPA filter in our Skoda. There are less effective aftermarket cabin/pollen filters available.

 

[Islineclear3_1]

Probably a bit late now but wonder what the readings might be at the height of the cold/flu season.... Or in a Voyager....

 

[modernrail]

I would be very interested to see the readings for the deep level tube lines compared to the shallow as well.

The Elizabeth line has platform readings are concerning. They are new although I suspect a lot of leakage into those platforms from the adjacent tube platforms.

I would be surprised if the platforms on the shallow level lines are much different to the above ground air. I suspect the trains are roughly equivalent to above ground.

I have a horrible feeling the levels on the deep level tube are hideous, both on platform and in train. The system seems to be sucking down, concentrating and recirculating very very dirty air and it seems to be getting a lot worse not better.

I have been actively avoiding the deep level tube for a while now.

Also, wasn’t there a story about IET’s in diesel mode being very bad because of the placement of the of the exhaust against the intake for the air conditioning system?

 

[DynamicSpirit]

I would be very interested to see the readings for the deep level tube lines compared to the shallow as well.

The Elizabeth line has platform readings are concerning. They are new although I suspect a lot of leakage into those platforms from the adjacent tube platforms.

I wonder if simply being underground is one of the main factors, considering the tendency of particulates to sink. Add to that being in a tunnel, so that any particulates from trains/people are more likely to hang around. The hypothesis that some is leakage from adjacent tube platforms could be tested by comparing with stations that are underground but have no adjacent tube platforms (Canary Wharf, Whitechapel, Farringdon, Paddington)

 

[boiledbeans2]

I would also like to see readings for the deep tube lines.

See post #30: https://www.railforums.co.uk/threads/air-quality-on-london-underground.249975/#post-6276285

 

[DarloRich]

no idea what any of this means. There are symbols used I have no knowledge off! Is there a "safe" level of Pm2.5 (?) exposure? Is it 500ugs/m or 5 ugs/m? If it is the former what are we worried about? if the later what should we do about it?


Can someone translate this into English and explain the point? It seems like a long winded posts asking for specifications of air conditioners! I need to understand ( as a non scientist) what the data is telling me, why it is important and what should be done with it.

 

[VP185]

I’m no expert on air quality levels but I have seen numerous posts regarding unsafe levels of CO2 on IETs, often exceeding 2,000ppm.

 

[Krokodil]

Annual average PM2.5 levels shouldn't exceed 5µg/m³. That doesn't mean that you can spend a month sitting in the smokebox of a steam loco without a dust mask on the basis that the other 11 months will bring your average down, you shouldn't exceed an average of 15µg/m³ over a 24hr period on more than three or four days per year

 

[snowball]

From the Guardian today:

Only seven countries meet WHO air quality standard, research finds

Almost all countries failing to meet mark for PM2.5, tiny particles expelled by vehicles and industry that can cause health problems

www.theguardian.com

Only seven countries are meeting an international air quality standard, with deadly air pollution worsening in places due to a rebound in economic activity and the toxic impact of wildfire smoke, a new report has found.

Of 134 countries and regions surveyed in the report, only seven – Australia, Estonia, Finland, Grenada, Iceland, Mauritius and New Zealand – are meeting a World Health Organization (WHO) guideline limit for tiny airborne particles expelled by cars, trucks and industrial processes.

The vast majority of countries are failing to meet this standard for PM2.5, a type of microscopic speck of soot less than the width of a human hair that when inhaled can cause a myriad of health problems and deaths, risking serious implications for people, according to the report by IQAir, a Swiss air quality organization that draws data from more than 30,000 monitoring stations around the world.

While the world’s air is generally much cleaner than it was in much of the past century, there are still places where the pollution levels are particularly dangerous. The most polluted country, Pakistan, has PM2.5 levels more than 14 times higher than the WHO standard, the IQAir report found, with India, Tajikistan and Burkina Faso the next most polluted countries.

But even in wealthy and fast-developing countries, progress in cutting air pollution is under threat. Canada, long considered as having some of the cleanest air in the western world, became the worst for PM2.5 last year due to record wildfires that ravaged the country, sending toxic spoke spewing across the country and into the US.

In China, meanwhile, improvements in air quality were complicated last year by a rebound in economic activity in the wake of the Covid-19 pandemic, with the report finding a 6.5% increase in PM2.5 levels.

“Unfortunately things have gone backwards,” said Glory Dolphin Hammes, North America chief executive of IQAir. “The science is pretty clear about the impacts of air pollution and yet we are so accustomed to having a background level of pollution that’s too high to be healthy. We are not making adjustments fast enough.”

Air pollution kills an estimated 7 million people a year worldwide – more than Aids and malaria combined – and this burden is most heavily felt in developing countries that rely upon particularly dirty fuels for heating, light and indoor cooking.

The most polluted urban area in the world last year was Begusarai in India, the sixth annual IQAir report found, with India home to the four most polluted cities in the world. Much of the developing world, particularly countries in Africa, lacks reliable air quality measurements, however.

The WHO lowered its guideline for “safe” PM2.5 levels in 2021 to five micrograms per cubic meter and by this measure many countries, such as those in Europe that have cleaned up their air significantly in the past 20 years, fall short.

But even this more stringent guideline may not fully capture the risk of insidious air pollution. Research released by US scientists last month found there is no safe level of PM2.5, with even the smallest exposures linked to an increase in hospitalizations for conditions such as heart disease and asthma.

 

[DynamicSpirit]

From the Guardian today:

Only seven countries meet WHO air quality standard, research finds

Almost all countries failing to meet mark for PM2.5, tiny particles expelled by vehicles and industry that can cause health problems

www.theguardian.com

Unsurprisingly, almost of those 7 countries are either islands surrounded by oceans or have very low population densities, so I would imagine the reason that those countries have such low PM2.5 levels is geography rather than anything particularly good that their Governments are doing. Estonia is the only one on that list that I'm surprised about.

 

[Krokodil]

Australia is a surprising inclusion, given that it is pretty car-centric and suffers from wildfires.

 

[H&I]

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.

Thank you for your insight. I had been meaning to buy a PM2.5 monitor for a while now to monitor air quality on my daily Northern line commute, so thank you for reminding me.

At what times of the day did you make these measurements? A previous study on the London Underground showed that on platforms, PM2.5 and PM10 levels peak in the evening.

We studied the number-size distribution and physico-chemical characteristics of ultrafine (PM0.1), fine (PM0.1–2.5) and coarse (PM2.5–10) particles collected on a London underground platform. Particle number concentrations gradually increased throughout the day, with a maximum concentration between 18:00 h and 21:00 h (local time).

[1]

Did you take the measurements done on diesel multiple unit trains on motor coaches where the engines are, or did you take them on trailer coaches? I say this because a comparison of indoor particulate matter between motor coaches and trailer coaches could be helpful to those deciding on which coach to sit in.

I do think that air quality is something the rail industry needs to tackle seriously if it wants to have serious green credentials.

[1] https://www.sciencedirect.com/science/article/pii/S0048969722064142?via=ihub

 

[Krokodil]

Did you take the measurements done on diesel multiple unit trains on motor coaches where the engines are, or did you take them on trailer coaches? I say this because a comparison of indoor particulate matter between motor coaches and trailer coaches could be helpful to those deciding on which coach to sit in.

Other than IETs, how many DMUs have trailer cars these days?

 

[allotments]

Thank you for your insight. I had been meaning to buy a PM2.5 monitor for a while now to monitor air quality on my daily Northern line commute, so thank you for reminding me.

At what times of the day did you make these measurements? A previous study on the London Underground showed that on platforms, PM2.5 and PM10 levels peak in the evening.

[1]

Did you take the measurements done on diesel multiple unit trains on motor coaches where the engines are, or did you take them on trailer coaches? I say this because a comparison of indoor particulate matter between motor coaches and trailer coaches could be helpful to those deciding on which coach to sit in.



I do think that air quality is something the rail industry needs to tackle seriously if it wants to have serious green credentials.

[1] https://www.sciencedirect.com/science/article/pii/S0048969722064142?via=ihub

I sampled air ad hoc at different times of day including evenings

Bear in mind some of the data being discussed above wasn't reported by me

As you suggest, it would be good to check air throughout a train to find differences but I'm typically unable to walk the train as I travel with a loaded bicycle. Some trains might have suboptimal filtration. I've found some carriages don't reduce PM2.5 between stations, even though similar carriages do this.

This week I travelled from Abbey Wood on Elizabeth Line. Air was good until I exited the train at Tottenham Court Road. PM2.5 at platform level below the long escalator to street was 50µg/m3. Outdoors PM2.5 was 5µg/m3. I wonder whether ventilation is drawing dirty air from older tube tunnels there?

In the VW Golf example above, was that with the aircon on and on recirculate? It should/could have HEPA filters and the like in circuit just like a train with much the same result unless there's other considerations.

I've found the cabin filter in the VW T-ROC. It was a VW original fitting that looked used. Nothing I can find in the climate control instructions to suggest anything other than air is filtered continuously in all settings. I've ordered a new Bosch Filter+ which is specified to remove 99.75% of PM2.5 and will try that. The standard Bosch filter for the vehicle filters out larger PM10 particles but not PM2.5.

I'll report back when I've fitted and tested this.