Without a doubt most orbs probably are dust particles, moisture, weed pollen etc. Is their any orbs that could be spirit energy?, i do think their could well be a tiny percentage of orbs that could be made of this spirit energy, i can only speculate though. Without a doubt also that most paranormal researchers and enthusiasts believe that most orbs if not all are dust particles, moisture and so on. I personally don't put any merit whatsoever in orbs, the minority of paranormal enthusiasts believe some are in fact spirit energy.
Here is a interesting discussion the topic of orbs hosted by medium Marcel Cairo