function growthfactor1 {dimensionless}
              (d1, {diameter of small neutral particle : nm}
               d2, {diameter of large charged or neutral particle : nm}
             gcm3, {small particle density : g cm-3, typically 1.5-2}
                q, {large particle charge : e}
                T, {air temperature : K}
               mb, {air pressure : mb}
              yua, {first dipole enhancement coefficient}
              yub  {second dipole enhancement coefficient} : real) : real;
                   {Uses external function "electrical_mobility_air"
    Presumption: condensing substance is expected not to evaporate
    Growthfactor1 = (Growth rate) / (Plain Knudsen growth rate), see
    "Tools for air ion and aerosol calculations" and (Tammet, Kulmala, 2005)
    Applicable for growth units of d < 0.7 nm, e.g. sulphuric acid

    This function is an impementation of the method of Nadykto and yu.
    yua = sqr(f1 - 1) / (f2 - 1) and yub = ln((f1 - 1) / (f2 - 1)),
    where f1 is the Nadykto-Yu dipole enhanchement factor for d = 1 nm
    and f2 is the Nadykto-Yu dipole enhanchement factor for d = 2 nm.
    Nadykto and Yu expected f1 = 4.35 and f2 = 1.8 for sulphuric acid
    at temperature 298 K, in this case yua = 14 and yub = 1.43

    Alternative methods are used in functions growthfactor0 and growthfactor2}

   const {that could be edited or moved to the list of parameters}
      h = 0.115; {extra distance : nm}
      d0 = 2.5; {critical diameter of quantum rebound : nm}
      T0 = 300; {extra temperature of quantum rebound: K}
   var x, y, d, b, m1, m2, g, p, k, u : real;
   begin
      x := 8.674e-23 * T; {2*pi*k*T : SI}
      d := 1e-9 * (d1 + d2 + 2 * h); {2 * delta : SI}
      m1 := 5.236e-25 * gcm3 * d1 * d1 * d1; {SI}
      m2 := 5.236e-25 * gcm3 * d2 * d2 * d2; {SI}
      b := 6.2414e14 *                {B1 + B2 : SI, 0.62414 = 1/1.6022}
           (electrical_mobility_air (mb, T, gcm3, 0, d1) +
            electrical_mobility_air (mb, T, gcm3, 0, d2));
      g := 2 * (b / d) * sqrt (x * m1 * m2 / (m1 + m2)); {gamma = Kc / Kk}
      y := (273 / (T + T0)) * exp (3 * ln (d0 / d2)); {quantum effect}
      p := sqr (y) * exp (y) / sqr (exp (y) - 1); {sticking probability}
      k {m3/s} := x * b * d /
         (1 + g - 0.299 * g / (exp (1.1 * ln (g)) + 0.64) + g * (1 - p) / p);
      u := sqrt (3.516e-23 * T / m1);
      y := 1.273e18 * k / (d2 * d2 * u);
      growthfactor1 := (1 + yua * exp (-yub * d2)) * y;
   end;