Yes I saw this on twitter. To the twitter I added a reference from my professional publication Chemistry World published by the Royal Society of Chemistry. The article is almost as equally damning.
Ultrafine particles and soot linked to lung cancer are massively elevated in carriages pulled by diesel engines
www.chemistryworld.com
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That article is a different study, made two years ago in Denmark, and contradicts the one in the Guardian
The Guardian "Passengers on trains pulled by diesel locomotives are more exposed to fumes when sitting in rear rather than front carriages, the researchers found",
RSC "Those sitting on carriages being pulled by a diesel engine, especially close to the engine, breathe in a much larger dose of diesel fumes". "‘I would recommend to passengers, particularly those susceptible to exposure, such as asthmatics, to sit as far as possible from the engine when the train is being pulled,’ Evans advises. ‘When the train is being pushed the air quality is a lot better everywhere.’"
Can anyone provide a link to the actual RSSB study? As far as I can see none of the trains described are loco-hauled except the HST on EMR. Sitting on top of the engine of course beings you much closer top the source of the fumes.