Condensation is the process by which atmospheric water vapour changes into water or ice crystals.
It is just reverse of the process of evaporation.
Process of condensation
The temperature of the air falls in two ways.
Firstly, cooling occurs around very small particles of freely floating air when it comes in contact with some colder object.
Secondly, loss in air temperature takes place on a massive scale due to rising of air to higher altitudes.
The condensation takes place around the smoke, salt and dust particles which attract water vapour to condense around them.
They are called hygroscopic nuclei.
When the relative humidity of an air is high, a slight cooling is required to bring the temperature down below dew point.
But when the relative humidity is low and the temperature of the air is high, a lot of cooling of the air will be necessary to bring the temperature down below dew point.
Thus, condensation is directly related to the relative humidity and the rate of cooling.