One way to address this question is via a theoretical development of the nucleation equations using the Gibbs energy. Heterogeneous nucleation on a wettable surface is preferred because the surface energy term is reduced. Another way to address this question is to invert the picture and consider vaporization. The vapor pressure of a curved surface is lower and effects such as Ostwald ripening are common from it.

Both approaches lead to the same conclusion. Heterogeneous condensation on wettable surfaces can occur at lower effective vapor pressures.

Thanks for the update Jeffrey J Weimer. But here the wettable surface is air. So does the same principle can be applied for condensation in air also?

Homogeneous nucleation is clean air. Heterogeneous nucleation is dusty air.

Thanks for the reply Jeffrey. Will look into that

The condensation at RH < 100% in a steady air - hmogeneous nucleation - impossible.

Under these conditions, the Condensation may occur due to dramatically change in atmospheric pressure - like blast wave, shock wave in the air or high turbulence fluents.

The condensation at RH < 100% in steady air may occur only in micronic pores on particles. But when the pores are filled with water, the condensation stops.

Condensation may occur on the cool/cold particles and droplets … and stops when dropets or particles "warmed up".

Additionally, there is the term the @hygroscopic growth@ — it is condensation of water vapor on the hygroscopic and superhygroscopic surfaces (and particles) - but it … not a condensational growth — because this type of condensation have a strong limitation and a lot of water vapor can not concentrate in this circumstance - only a thin layer of water on the hygroscopic surface.

Additionally / //

condensation on ultrafine (nanosized) nucleation sites has a some problem. See the Thomson equation (Kelvin) — pressure of water vapor under spherical surfaces// The smaller the particle, the more supersaturation (RH>100%) need to start condensation (for submicron and nano particles). 

Thanks Alex for the information. I will definitely look into it