function Knudsen_growthrate {nm h-1}
(dg, {diameter of a growth unit : nm}
gcm3, {density of growth unit substance: g cm-3}
ng, {number concentration of growth units: cm-3}
T {air temperature : K} : real) : real;
{Nucleating particles are expected to grow by condensation of a substance,
which particles are called the growth units. Growth units are molecules
or clusters. Plain Knudsen growth rate assumes the free molecule regime
when growth rate does not depend on the size of the growing particle}
const k = 1.38e-23; {Boltzmann constant}
var d, m, g : real;
begin
d := 1e-9 * dg; {internal calculations in SI}
m := (pi / 6) * d * d * d * (gcm3 * 1000);
g := (pi / 12) * d * d * d * (1e6 * ng) * sqrt (8 * k * T / (pi * m)); {SI}
Knudsen_growthrate := (1e9 * 3600) * g;
end;