How does rain clean the air and change sunset colours?

In one line

The rule

Rain helps clean the air by capturing and removing dust, smoke, and other pollutants as it falls. After rain, with fewer particles in the air, sunlight travels differently, which can change the colors we see at sunset.

Let's understand it simply

Imagine your mother sweeping the floor. She uses water to stop dust from flying everywhere. Rain does the same job for the air. When it rains, water drops fall through the air, catching dust, smoke, and tiny dirt particles. These get pulled down to the ground with the rainwater. After rain, the air feels fresh and smells clean because there are fewer dirty things floating around.

Now, think about a sunset. Normally, the sky can look orange, red, or even purple. This happens because sunlight passes through the air, and dust or pollution can change how the colors spread. After rain, with less dust, the colors can look brighter or sometimes softer, depending on what is left in the air.

How it works

1. Clouds form when water vapor (water in the air) cools and turns into tiny droplets.
2. These droplets join together and become bigger, forming raindrops.
3. As raindrops fall, they bump into dust, smoke, and pollution in the air.
4. The raindrops catch these particles and carry them down to the ground.
5. After rain, the air has fewer particles, so sunlight travels more clearly.
6. At sunset, with less dust, the sky can look more blue or pink, and sometimes the colors are sharper.

The story behind it

Scientists have studied how rain cleans the air for many years. The process is called wet deposition (removal of particles by rain). In the late 1800s, scientists noticed that after rain, people with breathing problems felt better. Later, researchers like John Tyndall and Lord Rayleigh explained how sunlight changes color in the sky, which is called scattering (spreading of light in different directions).

Where you see it in real life

• After a heavy monsoon rain in Delhi: The air feels cooler and fresher, and you can see far away buildings more clearly. Rain has washed away dust and smoke.
• Village cricket match after rain: The sky looks bright blue, and the sunset is clear, with fewer orange or red colors. Less dust means less scattering.
• Diwali fireworks before and after rain: Before rain, smoke from crackers makes the air hazy. After rain, the smoke is gone, and the sky looks cleaner.
• City traffic during rain: The usual smell of petrol and smoke is less. Rain has cleaned the air.
• Sunset on a rainy day: Sometimes, the sky looks pink or purple, and the colors are softer because the air is cleaner.
• Morning after rain in the fields: The air smells fresh, and you can see the sunrise more clearly.

Why it matters

• Health: Clean air after rain helps people breathe better, especially those with asthma or allergies.
• Visibility: Drivers and pilots can see better when the air is clean.
• Crops and plants: Clean air is better for growing food, as dust and pollution can harm plants.
• Science: Understanding how rain cleans the air helps us fight pollution and keep cities healthier.

Worked example

Let’s say before rain, the air has 200 micrograms of dust per cubic meter. After a heavy rain, it drops to 50 micrograms.

Given: Dust before rain = 200 µg/m³, Dust after rain = 50 µg/m³
Step 1: Find the difference: 200 - 50 = 150 µg/m³
Step 2: Calculate the percentage removed: (150 / 200) × 100 = 75%
Step 3: Answer: Rain removed 75% of the dust from the air.

Common mistakes

• Thinking rain always makes sunsets more colorful: Sometimes, rain makes colors softer, not brighter, because there is less dust to scatter the light.
• Believing rain removes all pollution: Rain removes a lot, but not everything. Some gases and very tiny particles can stay.
• Confusing fog with pollution: After rain, you might see fog, but it is just water vapor, not dirty air.
• Assuming only rain cleans the air: Wind and plants also help clean the air, not just rain.

Remember it

Rain is nature’s sweeper — it washes away dust and pollution, making the air clean and changing how we see the sunset.