Re: 3d fireworks. Pre or Post

One really fast 'cheat' might be possible if your buildings offer fairly simple reflective surfaces (i.e. they're all parallel and flat, without curves or complicated indentations).

What a mirror does is create the visual illusion that objects exist beyond the mirror. So an object sitting 1 foot away from a mirror appears to have a twin which is 2 feet away from it, measured directly towards the mirror (1 foot to get to the mirror, then 1 additional foot inside).

So one possibility is to set up some fireworks in Maya (yes, avoid the canned Effect) with a 'twin' being rendered in the appropriate position in space to look like the reflection. That is, have it render inside the building. You would want to render this pass separately, so that you could tweak colours, maybe blur it a little, and of course mask it so that it only appears where the face of the building is.

As I say, this is heavily dependant on the structure of your city! If you have multiple bursts reflected from different angles, it is probably not worth the effort--but it might be a quick fix if you've got a fairly simple layout.

Beyond that... remember that Maya's hardware particles will not, as far as I know, show up in raytraced reflections. I'm not sure how any of Maya's particles interact with Mental Ray, either.

Good luck,

-Steve