Evaporation, the process by which the substance or compound transitions from its liquid phase to its gas phase below the level at which it boils; in particular, the process by which the liquid water enters the atmosphere as water vapour. Evaporation, often from the sea and trees, replenishes the humidity of the air.

It is a key element in the energy sharing of the Earth-atmosphere system that produces atmospheric activity, climate, and weather. The rate of evaporation depends on the temperature difference between the evaporative surface and the air, relative humidity, and wind.

Define Evaporation

• Evaporation is a process by which water is converted from liquid to gas.
• Temperature is the main cause of evaporation.
• The latent heat of vaporization is called the temperature at which the water starts to evaporate.
• The rise in temperature increases the absorption of water and the concentration of air in the parcel.
• Air movement replaces an unsaturated layer with a saturated layer.
• The greater the motion of the air, the greater the evaporation.

Evaporation and Humidity

• Evaporation, especially from the sea and soil, fills up the humidity of the air. It is the transformation of liquid water into a gaseous state, but diffusion is studied. The rate of spread or evaporation is commensurate with the difference between the pressure of the water vapour in the free air and the vapour next to the saturated evaporative material.
• When liquid and air have the same temperature, evaporation is proportionate to the saturation deficit. The medium conductivity between the evaporator and the open air is also proportionate. Conductivity increases with airflow when the evaporator is open water.
• However, if the evaporator is a leaf, the moving water will pass through the silent air in the minute pores between the inside of the water and the outside of the dry air. In this case, porosity could change conductance more than ventilation.

• However, the evaporator temperature seldom corresponds to the evaporator temperature of around 600 calories (2500 joules) per gram, which cools the evaporator. The available energy for heating the evaporator is therefore as important as the deficiency of saturation and air conductivity.
• Some of this heat is transferred outdoors by convection from the surrounding air, but much of it must be radiated. Evaporation occurs more easily on sunny days than on cloudy days, not only because the sun is drier, but because the sun warms the evaporator and therefore raises the vapour pressure of the evaporator.
• In fact, this water loss is basically determined by the net radiation balance of the day according to the well-known Penman evaporation estimate (the balance which considers potential evaporation to be a function of humidity, wind speed, radiation, and temperature).

Define Condensation

Condensation, absorption, typically on surfaces that are cooler than the gas adjacent to the liquid or solid from its vapour. When the vapour pressure of the material exceeds the liquid or solid-phase vapour pressure of the substance at the surface temperature when the condensation happens, the substance is condensed.

The heat is released as the vapour condenses. The surface temperature increases until it is the same as the surrounding vapour unless the heat is removed.

• Conversion of water vapour to water.
• The lack of heat causes condensation.
• Once the saturated air is refreshed, it will reach the stage when its water vapour power ceases.
• Excess water vapour is concentrated in the fluid level.
• In free air, condensation causes very small, hygroscopic condensation nuclei particles to cool down.
• The level of cooling and the relative humidity of the air depends on the condensation.
• Climate, temperature, pressure, and humidity are affected.

Condensation Occurs as Follows

• When the air temperature decreases to a constant volume dew point.
• If the volume and temperature are decreased.
• If evaporation adds to air moisture. However, a decrease in air temperature is the most suitable condensation situation.

Process

• Cloud drops and ice crystals, which are allergic to the Earth's atmosphere, are associated with suspended aerosols created by both natural processes and human activities. In the absence of these aerosols, the relative humidity requirements would be well above 100 per cent compared to the flat H2O surface for the spontaneous conversion of water vapour into liquid water or ice crystals.

• Cloud forming in this way is called homogeneous nucleation, which occurs only in a controlled lab environment. Air containing more than 100 per cent relative humidity of water vapour shall be called supersaturated with respect to a flat surface.
• Aerosols in the atmosphere serve as a place where water vapour is accumulated or stored. Owing to their surfaces of distinct dimensions, aerosols minimize the amount of supersaturation required to change the water vapour phase and are known as cloud condensation nuclei.
• The higher the aerosol and the more solution, the less supersaturation the condensation surface requires for the aerosol. The condensation nucleus in the atmosphere will operate at supersaturations of about 0.1 to 1% (that is, levels of water vapour around 0.1 to 1 per cent above the point of saturation).
• Cloud condensation nucleus concentrations in the lower troposphere at 1% over-saturation vary from approximately 100 per centimetre (about 1,600 per centimetre) in the size of oceanic air to 500 per centimeter (8,000 per centimetre) in the atmosphere of the continent. Higher concentrations occur in polluted air.

• The ice nuclei are known as aerosols, which are effective in turning water vapor into ice crystals. Unlike the Cloud condensation nuclei, the ice molecule with a molecular spacing and a crystallographic structure near the ice (with a low water affinity) is hydrophobic.
• While the cloud condensation nuclei can be found in the atmosphere, it is often scarce. As a result, liquid water refreshing below 0 C, due to the lack of strong ice cores, will also continue to be liquid at subfreezing temperatures. Supercooled water is known to be liquid water at temperatures below 0 C.
• All other ice crystals, with the exception of true ice crystals, which work at 0 C, are effective at freezing temperatures. If no ice core is present, temperatures at or below-39 °C (−38 °F) are required when supercooled water droplets freeze within a radius of a few micrometers in a process known as homogeneous ice nucleation.
• When the rain falls close to 0 degrees, tiny cloud droplets have too few molecules to create ice crystals spontaneously as the temperature exceeds 39 degrees Celsius until the molecular movement slows down. Heterogeneous nucleation of ice can occur at warmer temperatures where ice cores are present.
• There are three types of ice cores: deposition nucleus, contact nucleus, and freezing nucleus. The deposition nucleus in that water vapor deposits directly as ice crystals in the aerosol is close to the patronizing nucleus.

• Conversely, the conversion of supercooled water to ice is related to the contact and freezing of the nucleus. A contact nucleus transforms liquid water into ice by touching a supercooled water droplet. The freezing nucleus is dissolved into liquid water and turns supercooled water into ice from the inside out.
• Examples of cloud condensation nuclei include sodium chloride (NaCl) and ammonium sulfate ([NH4]2 SO2), while clay mineral kaolinite is an example of ice nuclei. By comparison, naturally occurring bacteria found in decayed leaf litter can serve as ice cores at temperatures below −4 °C (24.8 °F). Silver iodide, with active ice-nucleating temperatures of less than −4 °C, has been used for years as a means of converting supercooled water into ice crystals in regions with a lack of natural ice cores.

FAQs

Question. What is evaporation?

Question. What factors influence evaporation?

Question. What is condensation?

Question. How are evaporation and condensation related?

Question. Why is evaporation important in the water cycle?

MCQs

1. Which of the following factors does NOT affect the rate of evaporation?

A) Temperature

B) Wind speed

C) Color of the surface

D) Humidity

2. What happens during condensation?

A) Water changes from liquid to gas

B) Water changes from gas to liquid

C) Water freezes into ice

D) Water evaporates into the atmosphere

3. What is the relationship between evaporation and condensation in the water cycle?

A) They are independent processes

B) They are two stages of water movement between Earth and the atmosphere

C) Evaporation leads to freezing

D) Evaporation causes precipitation

4. Which of the following will increase the rate of evaporation?

A) Decrease in temperature

B) Increase in humidity

C) Increase in surface area

D) Decrease in wind speed

5. Where does condensation primarily occur in the water cycle?

A) On the surface of the Earth

B) In the clouds in the atmosphere

C) In rivers and lakes

D) On the ocean's surface

GS Mains Questions and Model Answers

Q1: Explain the processes of evaporation and condensation and their role in the water cycle.

Answer: Evaporation is the process where water is heated and changes from a liquid to a gas, rising into the atmosphere. This is typically driven by solar energy, which heats the surface of oceans, lakes, and rivers. Condensation occurs when the water vapor cools and turns back into liquid form, forming clouds. The water cycle is driven by these processes, as water evaporates from Earth's surface, moves through the atmosphere, and condenses to form clouds. These clouds then release water as precipitation, completing the cycle and ensuring the movement of water between the surface and the atmosphere.

Q2: Evaluate the significance of evaporation and condensation in regulating climate and weather patterns.

Answer: Evaporation and condensation are essential for regulating global climate and weather patterns. Evaporation from the oceans, lakes, and rivers releases water vapor into the atmosphere, which helps maintain the Earth's energy balance. The heat energy required for evaporation comes from the sun, which helps drive atmospheric circulation. Condensation of water vapor into clouds results in the release of latent heat, which warms the surrounding air and influences atmospheric pressure, wind patterns, and precipitation. This cycle is crucial for weather formation and helps regulate temperatures, contributing to the stability of the global climate system.

Q3: Discuss the impact of increased humidity on the processes of evaporation and condensation.

Answer: Increased humidity, or the amount of water vapor in the air, can significantly slow down evaporation, as the air becomes closer to saturation and can hold less additional moisture. In contrast, high humidity enhances condensation because the air is already holding a significant amount of moisture, making it easier for the water vapor to cool and condense into liquid form. This can lead to the formation of clouds and precipitation. Therefore, the balance between evaporation and condensation is heavily influenced by the humidity levels in the atmosphere, which affects both the rate of evaporation and the likelihood of rainfall or cloud formation.

Previous Year Questions on Evaporation and Condensation

1. UPSC CSE 2018

Question: "Explain the role of evaporation and condensation in the water cycle and their impact on weather patterns."

Answer: Evaporation and condensation are fundamental to the water cycle. Evaporation moves water from the surface of the Earth into the atmosphere as water vapor, driven by solar energy. As the vapor rises and cools, condensation occurs, forming clouds and releasing latent heat. This process regulates atmospheric temperature, pressure, and circulation, contributing to the formation of weather systems. Evaporation helps maintain global climate by redistributing heat, while condensation influences precipitation, which directly impacts regional weather patterns.

2. UPSC CSE 2020

Question: "Discuss the factors influencing evaporation and condensation in relation to the water cycle."

Answer: Factors influencing evaporation include temperature, wind speed, humidity, and surface area. Higher temperatures and wind speed increase evaporation rates, while higher humidity reduces it. Surface area also plays a crucial role, as larger areas facilitate more evaporation. Condensation is primarily influenced by cooling of the air and saturation of water vapor. When the air cools to its dew point, the vapor condenses into liquid, forming clouds. Understanding these factors is essential for predicting weather patterns and managing water resources effectively.