Blue Noon

Blue Noon is a rarely used and somewhat ambiguous term, generally referring to a situation where the sun is overhead (noon) but the light has an unusual blue tint. This effect is most commonly associated with specific atmospheric conditions such as:

• Volcanic Eruptions: Large-scale volcanic eruptions can eject significant quantities of sulfur dioxide into the stratosphere. This gas then forms sulfate aerosols which can scatter sunlight. If the size of the aerosol particles is approximately one micrometer, they tend to preferentially scatter red light, allowing more blue light to pass through, resulting in a blue-tinged sky and sunlight, even at noon. This effect has been observed after major eruptions like Krakatoa in 1883 and Mount Pinatubo in 1991.
• Large Forest Fires: Extensive wildfires can release vast amounts of particulate matter into the atmosphere. Similar to volcanic aerosols, these particles can selectively scatter red light, creating a blueish hue in the sky, including during the midday hours.
• Industrial Pollution: In highly polluted areas, specific types of industrial emissions containing appropriately sized particulate matter might contribute to a blue noon effect, though this is less common and generally less pronounced than the phenomena caused by volcanic activity or forest fires.

The "blue noon" effect is typically a transient phenomenon, lasting for days or weeks depending on the persistence and distribution of the atmospheric particles causing the scattering. The intensity of the blue tint can vary depending on the density of the particles and the angle of the sun.

While visually striking and potentially beautiful, a blue noon is usually indicative of a significant environmental event impacting atmospheric composition and air quality.