The Blue Mountains appear blue primarily due to a natural phenomenon involving the scattering of light and the release of oils by the native trees. The blue hue is caused by tiny droplets of eucalyptus oil released by the abundant eucalyptus trees in the area. These oil droplets mix with dust particles and water vapor in the atmosphere, which scatter sunlight, especially the shorter blue wavelengths, creating a bluish haze over the mountains. This effect is known as Rayleigh scattering, the same phenomenon that makes the sky appear blue. Because blue light has shorter wavelengths and scatters more easily than other colors, the mountains seen from a distance take on a bluish tint. This natural blue haze, combined with the specific vegetation in the area, gives the Blue Mountains their iconic color.
In the case of the Blue Ridge Mountains in the US, a similar blue appearance comes from isoprene—an organic compound released by trees such as oaks that interacts with ozone to create a blue haze, showing another example of how tree emissions contribute to the blue appearance of distant mountain ranges.
Thus, the blue color of the Blue Mountains is a combination of tree-released oils, atmospheric scattering of light, and the specific environmental conditions creating the distinctive blue appearance from afar.
