Complete nonsense. Use a light emitter.
If you are trying to use the motion track applied to the null to move the Emitter (light) then you have two problems. First, you should not try and tie a 3D layer or position to a 2D layer. IOW, your null must be 3D even if your tracking data is 2D.
Second, when you parent the light to the null some interesting things happen. First, the light is not going to end up at the same position as the null unless you move the light to the position of the null to start with. If you don't do that, then parenting will just move the light relative to the null but they will not be in the same position. If it were me I would just use a simple expression to tie the position of the light to the null. Reveal the null's spoliation property, then Alt/Option click on the stopwatch for the Light's position and drag the expression pickwhip to the null's position property. You'll get an expression that looks like this:
Second problem I see is in your question. I'm not sure what you mean when you say the particles hang there in their own space. If you want the particles to create a smoke trail then you need to adjust the physics factors so that the particles react like smoke. Here's a sample project where I just used the Smoke preset for Particular, changed the emitter to a light, and then used the expression shown above to tie the light (Emitter) to the animated null.
I did. The light emitter was then parented to a null. But no worries, I figured out how to keep the trail of particles in track with the rest of the comp.
Thanks. What I meant is that the trail of particles didn't motion track with the rest of the comp, though the emitter did. So if the camera would pan a bit the trail wouldn't, though the emitting point and particles born during the pan would, if that makes sense.
I ended up figuring out the problem by making my 2D null into a 3D layer and inverting it on the x and 7 axis. Then by parenting my camera to it I had everything tracked in properly.