Three types of atmospheric scattering — classified by particle size relative to wavelength.

• Rayleigh scattering — particles ≪ λ (air molecules). Inverse-λ⁴ dependence — affects shorter wavelengths most. Why the sky is blue.
• Mie scattering — particles ≈ λ (dust, smoke, pollen, aerosols). Influences longer wavelengths / all visible. Creates hazy skies.
• Non-selective scattering — particles ≫ λ (cloud droplets, ice). Affects all wavelengths equally → clouds appear white because blue, green, and red are all scattered in the same proportion.