Tyndall effect, a beautiful negative indicator

  Have you ever seen “the sun shining out of the sky”?
  Some time ago, this scene appeared in Shuangfeng County, Hunan: the sun shot a white beam of light through the gaps in the clouds, piercing the sky, and the ten thousand rays of light hung in the sky. It was so beautiful… People took pictures and swiped the screen of the circle of friends. The scene also appeared in the hot search on Weibo. While being shocked by this landscape, many netizens are also asking, what makes the sun so beautiful?
  In the early western civilization, people called this light “Jesus light”, which is the light that flashed when Jesus was born. We can also see this element in many famous religious paintings. And now, we know that this is a weather phenomenon, thanks to the famous British physicist Tyndall. In 1869, Tyndall discovered the phenomenon of light scattering (or opalescence), and this phenomenon was therefore named “Tyndale phenomenon” or “Tyndale effect”.
  The Tyndall effect is related to the reflection of light: when light is propagating, it will be affected by colloidal particles, resulting in a “light path”. When the sun is irradiated, the dust and fog in the atmosphere are exactly on the projection surface of the sun, and then pass through the thicker clouds to illuminate it, forming a visual effect of rays of light.
  In fact, in our daily lives, we can also create the Tyndall phenomenon. For example, if you take a flashlight and irradiate a transparent colloid, when a beam of light passes through the colloid, you can see a “light path” appearing in the colloid from the direction of the incident light. This is because the particle size of the colloidal particles is 1-100nm (nanometers), and the visible light wavelength range is 390-760nm. When light enters the colloid, since the particle size of the colloid particles is smaller than the wavelength of visible light, light scattering occurs, which also produces the Tyndall effect.
  The Tyndall effect appears for a short time. If you are lucky, you should take a photo of it as soon as you see it, and then slowly appreciate it. Fortunately, it is also easy to “capture”, and the time and place of appearance are relatively fixed: generally in the early morning, at sunset, and when there are more clouds after the rain; it mainly appears in wooded areas. Because of its beauty, people have given it a lot of romantic and literary descriptions, such as “With Tyndall effect, just take shape”…
  Although the Tyndall phenomenon is beautiful, from the perspective of environmental protection, the appearance of the Tyndall effect also indicates that the air is polluted.

  The Tyndall effect is related to the presence of fog and dust in the air. Once the environment is polluted and the dust in the atmosphere reaches a certain proportion, the Tyndall effect will be produced when the weather is met. On the contrary, if the air is fresh and clean, it is difficult for people to see this kind of light.
  Specifically, the Tyndall effect is largely dependent on the most common fine particles and pollutants in our lives, which are also known as the medium that increases the value of PM2.5. This refers to particles with an “aerodynamic equivalent diameter” less than or equal to 2.5 microns. This kind of particulate matter can be suspended in the air for a longer time, and the more content in the air, the more serious the air pollution. And because the particles are small, it is easily inhaled into the lungs, which is harmful to health. In the past decade or so, many environmentalists have called for a ban on fireworks during the Spring Festival and weddings, hoping not to increase air pollution.
  Therefore, when the Tyndall phenomenon occurs, we must also be aware that the air has already been polluted to a certain degree at this moment. Therefore, the Tyndall effect is also used to detect the concentration of fine particles and pollutants in the air. For example, some car brands will use the Tyndall effect to prove the performance of the car’s air circulation system when they hold events.
  No wonder some people say that the Tyndall effect is brilliant, beautiful and terrifying!