function ion_needlesink {s-1}
          (Z {ion mobility : cm2 V-1 s-1},
     dneedle {mm, about 0.9 for Pinus Sylvestris},
           L {m-2, total length of needles in 1 m^3 of the canopy},
        wind {m s-1, inside of the canopy},
           T {air temperature : K},
          mb {air pressure : mb} : real) : real;
   var nyy, Re, Sc, kTB : real;
   begin
      kTB := 8.62e-9 * T * Z;
      nyy := 5.5e-7 * exp (1.8 * ln (T)) / mb;
      Re := (wind * dneedle / nyy) / 2000;
      Sc := nyy / kTB;
      ion_needlesink := kTB * L * (0.3 +
         0.62 * sqrt (Re) * exp (0.33333 * ln (Sc)) *
         exp (0.8 * ln (1 + exp (0.625 * ln (Re / 282000)) )) /
         sqrt (sqrt (1 + exp (0.66667 * ln (0.4 / Sc)) ))       );
   end;