SCATERRING AND ABSORBTION OF DIFFERENT PARTICLES

1. Types of Atmospheric Scattering &
Absorption
• Rayleigh Scattering
• - Occurs when particles are very small
compared to the wavelength.
• - Caused by nitrogen & oxygen molecules,
small dust specks.
• - Shorter wavelengths (blue) are scattered
more than longer ones.
• - Dominant in the upper atmosphere.
• - Sky appears blue due to scattering of blue
light.

2. Mie Scattering
• - Happens when wavelength ≈ particle size.
• - Longer wavelengths scattered more than in
Rayleigh scattering.
• - Scattered light intensity 1 / wavelength.
∝
• - Caused by aerosols: dust, smoke, pollen.
• - Gas molecules don’t cause Mie scattering.

3. Non-selective Scattering
• - Occurs when particles are much larger than
the wavelength (≈10×).
• - Caused by water droplets, ice crystals,
raindrops.
• - All wavelengths (visible & IR) are scattered
equally.
• - Clouds & fog appear white or grey due to
equal scattering.

4. Atmospheric Absorption
• - Retains radiant energy in the atmosphere.
• - Unlike scattering, energy is lost and re-
radiated at longer wavelengths.
• - Main absorbers:
• • Ozone (O₃) – absorbs UV radiation.
• • CO₂ – absorbs mid & far infrared, acts as
greenhouse gas.
• • Water vapour – absorbs long IR &
microwave radiation.