Humidity, evaporation, and condensation

In evaporation liquid water changes into water vapour. In process and state change questions check the correct result.

Relative humidity may be higher in the morning due to lower temperature and lower in the afternoon as temperature rises. Use temperature as the base for daily cycle.

Moist air rising along a mountain slope can cool to dew point. This can form orographic clouds and rainfall.

Higher relative humidity means air is closer to saturation. A little cooling can bring it to dew point and cause condensation.

Cool and humid air has less capacity to take more water vapour. Therefore evaporation becomes slow.

During the day, solar heat gives energy to water and the open surface supports evaporation. For exams, remember both heat and surface area.

Condensed droplets can join, become larger and fall as precipitation. Treat condensation as an important stage before rainfall.

Moist air may reach dew point on touching a cold surface and vapour changes into droplets. Link such daily examples with condensation.

Oceans provide a vast water surface so they are the major source of atmospheric water vapour. In the water cycle treat oceans as the main source.

Clouds reduce radiational cooling of the ground so the surface is less likely to reach dew point. A clear sky is more favourable for dew.

Absolute humidity is the actual amount of water vapour while relative humidity compares it with saturation capacity. In definition questions separate actual amount and percentage.

In fog tiny water droplets float near the surface and reduce visibility. In visibility questions identify fog.

At low temperature air has less capacity to hold moisture and high moisture brings it near saturation. In exams connect cooling and high moisture with condensation.

A lake supplies water vapour and night cooling can bring air to dew point. This forms fog near the surface.

When temperature rises air can hold more water vapour. Therefore warm air needs more moisture to become saturated.

Hot dry air can take more water vapour and an open surface increases evaporation. For exams remember temperature humidity and surface area together.

Dust particles act as condensation nuclei and water vapour changes into droplets. This helps in cloud and fog formation.

Pollution particles can act as nuclei for condensation and reduce visibility with moisture. Particles are important in urban fog.

On a clear calm night the ground cools quickly by radiation and may reach dew point. Therefore dew formation becomes more likely.

On a surface below freezing water vapour can deposit as ice crystals. In this condition frost forms.