I asked this on Reddit earlier this week, but nobody had much technical insight.
Can anyone shed light on why exhaust gas from a typical London bus smells entirely different from a coach or truck's exhaust? The latter smell like diesel always did, whereas London busses emit this strange, to me at least, intolerable smell of weirdness. When I walk past a bus, I take the deepest possible breath, and hold it until I'm clear of the bus. When I drive, I close the windows and set the airflow to recirculate instead of taking in outside air. I avoid ricing my bicycle behind a bus, at all cost.