Diffusion of light in the atmosphere takes place due to

Diffusion (diffuse) light in the atmosphere is produced primarily by scattering of sunlight by air molecules and suspended particles (aerosols, dust). Molecules cause Rayleigh scattering which preferentially scatters shorter (blue) wavelengths, while larger aerosols and dust produce Mie/non‑selective scattering that redirects sunlight in many directions, creating diffuse sky light [2]. Dust and other solid/aerosol particles are therefore key contributors to diffusion; water vapour and clouds can also scatter or absorb but act differently (cloud droplets cause non‑selective scattering and absorption), whereas trace gases like CO2 mainly absorb at specific wavelengths and noble gases such as helium have negligible effect on visible light diffusion. Thus “dust particles” is the best choice.

Sources

1. [1] https://www.pveducation.org/pvcdrom/properties-of-sunlight/atmospheric-effects
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 10: The Human Eye and the Colourful World > 10.6.2 Why is the colour of the clear Sky Blue? > p. 169