Answer to Question 1
Grains move by rolling or bouncing along the ground. Wind can move grains by picking up small particles and carrying them for a short distance. When the particles land, they knock loose other particles, either propelling those grains aloft or making them available for transport in the blowing wind. Very small dust particles can stay aloft and be transported for very long distances in suspension.
Answer to Question 2
The fine dust particles are very cohesive because of electrostatic attractions between the small particles.