Average levels of nitrogen dioxide were highest onboard GWR trains between London and Bristol
Micrograms per cubic metre
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Paddington to Bristol Temple Meads (GWR)
Euston to Birmingham New Street (Avanti West Coast)
Bletchley to Ridgmont/Bedford (West Midlands Trains)
St Pancras to Nottingham (East Midlands Railway)
Marylebone to Birmingham Snow Hill (Chiltern)
Ipswich to Cambridge (Greater Anglia)