Young Brunette Girl On The Sand At Sunset

After Rayleigh scattering has removed the violets, blues, and greens, people's viewing of red and orange colors of sunsets and sunrises is then enhanced by the presence of particulate matter, dust, soot, water droplets (like clouds), or other aerosols in the atmosphere, (notably sulfuric acid droplets from volcanic eruptions). Particles much smaller than the wavelength of the incident light efficiently enhance the blue colors for off-axis short path lengths through air (resulting in blue skies, since Rayleigh scattering intensity increases as the sixth power of the particle diameter). Larger particles as aerosols, however, with sizes comparable to and longer than the wavelength of light, scatter by mechanisms treated, for spherical shapes, by the Mie theory. Mie scattering is largely wavelength insensitive. Its spacial distribution is highly preferential in the forward direction of the incident light being scattered, thus having its largest effect when an observer views the light in the direction of the rising or setting Sun, rather than looking in other directions. During the daytime, Mie Scattering generally causes a diffuse white halo around the Sun decreasing the perception of blue color in the direction toward the Sun and it causes daytime clouds to appear white due to white sunlight. At sunset and sunrise, Mie scattering off of particles and aerosols across the horizon, then transmits the red and orange wavelengths that remain after Rayleigh scattering has depleted the blue light. This explains why sunsets without soot, dust, or aerosols are dull and fairly faint red, while sunsets and sunrises are brilliantly intense when there are lots of soot, dust, or other aerosols in the air.
Sunset colors are typically more brilliant than sunrise colors, because the evening air contains generally more particles and aerosols and clouds than morning air. Cloud droplets are much larger than the wavelength of light; so they scatter all colors equally by Mie scattering, which makes them appear white when illuminated by white sunlight during the daytime. The clouds glow orange and red due to Mie scattering during sunsets and sunrises because they are illuminated with the orange and red light that remains after multiple prior Rayleigh scattering events of the light from the setting/rising sun.
Ash from volcanic eruptions, trapped within the troposphere, tends to mute sunset and sunrise colors, while volcanic ejecta that is instead lofted into the stratosphere (as thin clouds of tiny sulfuric acid droplets), can yield beautiful post-sunset colors called afterglows and and pre-sunrise glows. A number of eruptions, including those of Mount Pinatubo in 1991 and Krakatoa in 1883, have produced sufficiently high stratospheric sulfuric acid clouds to yield remarkable sunset afterglows (and pre-sunrise glows) around the world. The high altitude clouds serve to reflect strongly-reddened sunlight still striking the stratosphere after sunset, down to the surface.