"Further, large diesel engines running heavy start-stop duty cycles like buses probably generates unproportionally more particles than just about everything else."
The good news: electric busses are coming. City busses will be huge winners from electrification, both for economic and environmental reasons. Greatly reduced fuel and maintenance costs, improved ride quality, less noise and pollution.
It seems to me that it's mostly dust from the road - busses are heavy, have larger tyres and wider track width.
Combined with the fact that the roads are heavily sanded and salted half of the year, and that they are swept rather than washed, for some reason often only once in the year, the roads are dirty.
I know that other cities wash the streets more or less constantly, but here they claim it won't help which seems questionable to me.
Winter tyres with studs are allowed here (in the winter) and are getting a lot of attention since they generate a lot of particles in laboratory tests - but it would be interesting to see what 3 months of grinding sand and salt in snow slush with heavy weight wheels will generate, with or without studs.
But yes : electric busses would be nice. With a soft driving filter applied...
The problem with cars in cities is not just the pollution, although that is a huge factor.
It is also the fact that they are grossly inefficient space-wise. The majority have only the driver (and maybe, maybe a single passenger) in an otherwise empty car. Congestion would be vastly reduced if we could get most of those people on public transport or bikes instead.
The good news: electric busses are coming. City busses will be huge winners from electrification, both for economic and environmental reasons. Greatly reduced fuel and maintenance costs, improved ride quality, less noise and pollution.