"I would recommend passengers to sit as far as possible from the engine ..."

[whole diary]

[Adrian]

Whilst I understand 81D's misgivings about diesel fumes in stations (and the worst by far that I have ever encountered is on the footbridge at Manchester Victoria where the DMUs^▸ (Diesel Multiple Unit) idle immediately below it), the original thread was about the on-train situation.

Something that crossed my mind is that these days the vast majority of stock is air conditioned and there isn't much stock still running with opening windows. As I see it therefore, if you are travelling in what is essentially a semi-sealed box, air pollution from outside whilst on the move is going to be minimal. And in addition, if pollution is coming into the coach via the aircon, it's not going to make any difference whatsoever which coach you are in.

So I suspect that this latest scare story report only really applies to older stock with opening windows.

 

Presumably there is some sort of filter at the air intake for air con.  But does it remove the fine particulates (PM2.5) that are now considered the most harmful?

[Bmblbzzz]

Some studies have found that the air inside a car is more polluted than the air at the side of the road. The problem appears to be that exhaust gases from the vehicles in front are sucked into the car, either by air-con or simply by motion. Presumably it's a similar basic problem with trains, albeit the fumes are coming from the train's own engine not other trains'. But it must vary a lot with airflow, which is going to be affected by all sorts of fixed and changing factors (like shape of vehicle and speed).

[stuving]

I think air-con is a red herring. It cools internal air, in most vehicles entirely by recirculating it. The external part of a train roof is of course just a heat exchanger rejecting heat to outside air. (More or less) fresh air for make-up, or for ventilation without the chillers in use, is what matters and that's what tends in cars to come from low down in front of the engine - good to avoid your own chariot's effluvia, less so in respect of the one in front's exhaust.

As to where the ventilation intakes are on trains, in general or specifically, I can't say I've looked. I vaguely recall seeing grilles on the sides of carriages, but they could for inlet or outlet. 

[Western Pathfinder]

Air conditioning in most vehicles actually conditions fresh air by cooling  after it has been drawn into the said vehicle through a particulates filtration unit usually referred to as a Cabin or Poles filter. This filters all the air drawn into the car regardless of whether the AC^▸ (Alternating Current, or can mean Air Conditioning, depending on context. The second meaning is often used in a railway context and more generally) is in operation.

[stuving]

Air conditioning in most vehicles actually conditions fresh air by cooling  after it has been drawn into the said vehicle through a particulates filtration unit usually referred to as a Cabin or Poles filter. This filters all the air drawn into the car regardless of whether the AC^▸ (Alternating Current, or can mean Air Conditioning, depending on context. The second meaning is often used in a railway context and more generally) is in operation.

You're right about cars - it seems the heater/chiller box is usually fed via a flap valve that selects all external air, unless you select recirculate in which case it all comes from the cabin. And as to the inlet, that used (on old cars like mine) to be a grille under the windscreen - that's gone, but I guess the inlet is still thereabouts.

But the point I was trying to make about all vehicles is that the freshness or contamination of the air does not depend on where the chiller is.

[Bmblbzzz]

This is all ultimately distraction though: the key is not avoiding sitting in the pollution, but avoiding making it in the first place.

[Trowres]

There has been a response to the RSSB^▸ (Rail Safety and Standards Board) work that identified problems with air quality on 80x class trains (and others):

https://www.gov.uk/government/publications/air-quality-onboard-trains-a-response-to-the-rail-safety-and-standards-board-report/air-quality-onboard-trains-a-response-to-the-rail-safety-and-standards-board-report

[Witham Bobby]

There has been a response to the RSSB^▸ (Rail Safety and Standards Board) work that identified problems with air quality on 80x class trains (and others):

https://www.gov.uk/government/publications/air-quality-onboard-trains-a-response-to-the-rail-safety-and-standards-board-report/air-quality-onboard-trains-a-response-to-the-rail-safety-and-standards-board-report

It's interesting that the report mentions in passing (as well as air quality on board trains) the air quality of transport hubs, including railway and bus stations.  But not airports, which, to my mind, are often claustrophobic and suffer very poor air quality.  Mostly, if you're waiting for a train at a mainline railway station, you can do it out in the fresh air, if you want to

[stuving]

This DfT^» (Department for Transport - about) response already had its own thread, less visibly, in the "How stuff works" board. The original RSSB^▸ (Rail Safety and Standards Board) report was discussed, inter very many alia, in the long IET^▸ (Intercity Express Train - replacement for HSTs (manufactured by Hitachi in Kobe, Japan)) problems thread from post 484.