Unity particle system square box problem

Whenever the fog covers the flame (Particle System), the flame emits square boxes.
But when is not covering the flame the flame works fine.
I have attached the before and after picture :

Seems like a limitation of fog over translucent object. If you do not insist on covering the fire particles with fog, change the shader of your translucent material to the equivalent under Mobile/Particles category which does not support fog.