Are diesel fumes worse?

[cml]

I've a few days working in an office and it involves a walk into town down a very busy road at peak time, which is reknown as having very poor air quality (that hasn't stopped the council allowing in-fill buildings all down each side foiling any chance of a cross breeze, but that's another story).

The fumes are unpleasant.

I notice that most cars (I'll say 80% for the hell of it) are diesels. Does this make a difference, i.e. are diesels worse for air quality (however you measure that)? What am I detecting in the air? Particles or what? It feels slightly sufficating.

[EDLT]

Diesel particulates (soot) are worse than petrol fumes. In some parts of the world they pay more attention to diesel emissions than the evil that is CO2.