I've created a white dot sprite and animated it by code and Sine behavior, you can create all you want.
By default, it's creating a dust mote each 0.3 seconds, you can change it as well as its vertical speed and random sizing range in the Event Sheet. The horizontal movement can be edited changing the Sine behavior selecting the "White" sprite.
Don't need the reward, i've been asking many questions to the community lately and it was time to give something back to it. I think this can be useful for some other people too .