mparticles anti-gravity by deflector or similar command



I’m trying to get my head around a scenario for mparticles which I thought was going to be fairly simple (but which I can’t figure out) - Can you please help me?!

What I’m trying to acheive is the demolition of a building which is activated by sweeping an object through the suspended particles, causing them to drop.

I thought maybe the mpswitcher with anti-gravity could work but I can’t figure out how to have it use a deflector to trigger only by time or age. Do you have another simpler solution otherwise?

Thank you!