Can we use both "participate at" and "participate in" interchangeably? Is there a difference between the two if any?
Participate is not tied to a particular preposition such as at or in. Like other verbs, it can be modified by a phrase beginning with a preposition. The choice of preposition will depend more on what commonly goes with the rest of the prepositional phrase, not on the verb. Some examples:
Everyone will participate in the weekly meeting.
I would like to participate at the $100 level.
Sheila wants to participate with me.
We participate through our parent organization.
I wondered about this as well. When I Google 'participate at or award' I find that both are used in relation to 'participating ... an award'. However, the number of hits returned at 'participating in the award' is about 25 times that of 'participating at the award'. So if you look at usage, participating seems to be more common while having the same meaning/use.
When it has to do with an event, activity or a program, the appropriate preposition is "in". For instance, participants in a training workshop, seminar, football gala etc. When any other preposition is used, that other preposition might just be introducing an additional phrase ( or information) and in that case "in" is implied and thus taken for granted. Eg participants at level two hundred performed so well. In this sentence, at level two hundred is just additional information. The full sentence might have read participants in the competition (who are) at level two hundred performed so well.