What controls the tendency of trace elements in different particle size fractions?
Crustal elements are essentially from soil which have undergone compaction during geologic processes.  Particles are then lifted into the air (e.g. by wind) and coarse particles from the soil are suspended in the atmosphere.  If the particulate is from wildfire, it is still of "natural origin", but the particulate is from a combustion source.  Combustion creates fine particles.

Anthropogenic particulate emissions are dominated by combustion sources, because so much of our industry and energy production uses combustible fuels.  Combustion creates fine particles.  However, there are still several anthropogenic sources that create coarse particulate (e.g. road dust, construction dust, agricultural processes, etc.).