title: How to get a smaller tail with a bunch of CAEmitterCells (fade out and/or scale down)
body: <p>I have a CAEmitterLayer animated along a bezierPath and my CEEMitterCell particles are made with an partly transparent gaussed-circle.png. these particles have a lifetime of 0.3 which leads to a small tail of my animated CAEmitterLayer-Particles. 
  I need to have the tail becoming smaller at the end and have the cells fade out to alpha = 0 over lifetime. I tried different combinations of parameter settings and I din't get it to work. I just made the end of the tail fatter, looking ugly wrong. 
  please, what are the necessary parameter settings here? Is this even possible with CAEmitterCells?</p>