Thus, the extinction coefficient has been approximated from the extinction cross-section times the number density of scatterers (Nv). Nv is the ratio of the porosity (P) to the volume of the scatters (𝑉 = 𝜋𝑑 ) and Cext is the scattering cross-section (i.e., 𝐶 = 𝐶 for non-absorbing pore). See Figures and for the results of these monodisperse dp calculations. Finally, the polydisperse extinction coefficient was found by taking a weighted sum of the contributions of various pore sizes across the measured pore size distribution : 𝛾 = 𝐶 , 𝑁 , = 𝐶 , (𝑁 /𝑉 ) = 𝐶 , ((6𝑃 × (𝑁 , /𝑁 ))/𝜋𝑑 , ) [𝐄𝐪. 𝐒𝟒]