ParticleSystem:setSizes
Sets a series of sizes by which to scale a particle sprite. 1.0 is normal size. The particle system will interpolate between each size evenly over the particle's lifetime.

At least one size must be specified. A maximum of eight may be used.
ParticleSystem:setSizes( size1, size2, size8 )
size1 number The first size.
size2 (nil) number The second size.
size8 (nil) number The eighth size.