How to achieve this "trail effect" - After Effects I'm trying to achieve the following effect:



Here is the problem: I can't achieve the effect using particles. Some of them spread and linger around. Is there a way to achieve a similar effect without using particles or is there a way to solve the extra particle issue? Thanks in advance.

I uploaded the animated version in youtube, so you all can see how the effect looks in motion.
A quick and dirty solution would be to try applying a fast blur effect over the particle layer to the point they look like smoke.