Part Two - Smoke

Now that you have some reference, it is easier to explain the smoke particles. Add another emitter with the following settings (right screenshot)

There are less smoke particles [Birth Rate (Rend.) = 800], which scale only to 3/4th of their original size [End Scaling = 75%] and live a lot longer [Life Time = 45 Frames]. But most important, they are allowed to spread more than the sparks were able to [Horizontal = 10-degrees]. So most of the smoke follows a similar path as the sparks, but some will rise (due to modifiers). Now let's take a look at what light sources I used here (see below)

The main smoke light is, of course, grayish. You will notice how it differs in two ways from the main spark light source. For one thing, it is a lot larger. But then again its brightness is turned to 4 - so it's almost off. This is the time to talk a little about how the light sources behave while being visible particles. Whenever two light sources are close together (overlapping), they add up. Try to make the smoke light source brighter. You will notice how the smoke will wash out everything else because it becomes too dense. Remember how I told you that the amount of particles and the thickness of the lights work together? If you have this bright smoke, you could cut the number of particles and would get a result looking somewhat the same. Which works best is for you to decide. I usually like more particles with smaller light sources. I tend to believe that the quality is better due to the fact that there is a "higher resolution" or "sampling rate of particles" (if I had a better machine I'd go right down to atomic level). But for most things, you don't need that many particles. So this is definitely something you should toy with.

The additional light source is only for more detail in the scene. Smoke is usually not colored in only one hue. So I used another light source which is colored differently. This adds some darker smoke. Notice how those lights are not in any parent - child relationship. The dark and the white smoke are independent (not like the bright spark and it's tail)