Essentially, sunlight is made up of R O Y G B I V, like the visible light in the electromagnetic spectrum.

When light travels through the atmosphere, it scatters at an amount that depends on its frequency.

Aerosols are tiny particles in the atmosphere. They cause the scattering of light.

As the sun sets, it travels through a thicker layer of the atmosphere when compared to the sun at noon.

Remember that sunlight is made up of different colors. When sunlight travels through this longer path in the atmosphere, blue light is scattered by more aerosols. By the time the light reaches our eyes, only colours such as red or orange are visible.

Blue light is scattered because the shorter the wavelength, the more it is spread out by the atmosphere. Also, because aerosols are so small, they don't affect longer wavelengths as easily.

There can be other colours of sunsets because of the different concentrations and sizes of aerosols in the atmosphere.

White/yellow sunsets are due to reduced scattering from a small amount of aerosols, so the wavelengths reach our eyes with equal intensities.

Purple skies after sunsets are because of how the red light from sunsets combine with the scattered blue light to create purple hues.

To answer my research question in one sentence...

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