Even if diesel trains didn't exist at all, unfortunately one would still be exposed to diesel fumes on the way to the station.
The walk from my house to my local station is entirely through alleyways away from roads, and the train service is 100% electric (apart from a few diesels passing through at speed). However this doesn't stop me breathing in disgusting fumes from the nearly-empty buses which insist on serving the station forecourt (even through often they don't actually drop off/pick up anyone) linking the local council estates, or the line-up of taxis sitting with their engines running particularly in winter. Frustrating and irritating, but sadly probably won't change.
How do all those planes leave the tarmac at Heathrow now that fossil fuels are obsolete?
If the DfT hadn't canned BiMode voyagers there would be vastly fewer exhaust fumes at New Street.