Fugitive Dust

- particles lifted into the ambient air caused by
man-made and natural activities such as the
movement of soil, vehicles, equipment, blasting,
and wind. This excludes particulate matter emitted
directly from the exhaust of motor vehicles and
other internal combustion engines, from portable brazing,
soldering, or welding equipment, and from piledrivers.

Which of all of these is the most significant contributor? 
    The least?