ρ: Actual particle density (g/cm)
ρ: Gas or sample matrix density (g/cm)
r: Least-squares coefficient of determination. The closer this value is to 1.0, the better the data fit to a hyperplane representing the relationship between the response variable and a set of covariate variables.  A value equal to 1.0 indicates all data fit perfectly within the hyperplane.
λ: Gas mean free path (cm)
D: Mass-median-diameter (MMD). The log-normal distribution mass median diameter. The MMD is considered to be the average particle diameter by mass.
σ: Geometric standard deviation. This value is determined mathematically by the equation:
:σ = D/D = D/D
The value of σ determines the slope of the least-squares regression curve.
α: Relative standard deviation or degree of polydispersity. This value is also determined mathematically. For values less than 0.1, the particulate sample can be considered to be monodisperse.
:α = σ/D
Re : Particle Reynolds Number.
In contrast to the large numerical values noted for flow Reynolds number, particle Reynolds number for fine particles in gaseous mediums is typically less than 0.1.
Re : Flow Reynolds number.
Kn: Particle Knudsen number.