Investigation of Cloud Seed in CERN Research Laboratories.

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Particles in the air

The air is made up of the smallest particles we know, which are stable in themselves: atoms and molecules. On the other hand, the air around us also carries many other small particles: lumps of matter that are too small to be seen in the eye. Like solids and other liquids, the tiny particles in the air are made up of many molecules that are bound together by electrical attraction.

These particles are so light that they move with the air. Slowly they fall to the ground because of gravity, but the movement of the air pushes them harder than the force of gravity pulls them down. Particles are flown around by the wind, and can travel far distances, even between continents, before they fall down into the earth. When there are many particles in the air, the sky becomes turbid and the visibility is impaired.

Near the ground, the largest particles in the air are usually dust particles or plant pollen. The smallest particles are small clusters of molecules that stick together. Agglomers can grow into atmospheric particles if other molecules collide with a cluster and stick to it. Of only a few molecules, and they are much smaller than dust or stamens. Smoke is also composed of particles. Smoke particles are larger than molecules but smaller than dust. When such particles come from human activity we call them “air pollution.” However, air pollution can also be caused by individual molecules of toxic gases.

Particles in the sky are important for two main reasons. First, the breathing of a lot of such particles is not healthy. For example, smoke emitted from a car or cigarette lighter can be from a drug. The second reason that the particles are important is that they are needed for the formation of clouds.

Create clouds

Clouds, whether they are large gray layers, white lumps and fluffy clouds or plane trails in the sky, all share a few things in common. The most important thing is that they consist of tiny water droplets called Cloud droplets. Cloud drops are created when hot air from the surface of the earth rises up and cools down slowly. Like the particles we mentioned earlier, the cloud drops are so small that they do not fall to the ground (unless it rains). The air around the drops of water and rising up pushes them, and gravity pulls them down so that in the end they simply float in the sky.

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In the atmosphere the water is in a state of gas, unless there is any surface where the water droplets can be infected or the weather is very cold (-38 ° C). When there is a surface that the water comes into contact with, they can undergo condensation, that is to turn into liquid, or to freeze on the surface as happens when ice is formed on the ground. However, there are not many available scents in the sky. Therefore, to create a “drop of a cloud” need tiny particles with a small surface area to which water droplets can be infected. These particles function as the seeds of the drop of the cloud, also called condensation nuclei. In order for the droplet to form, particles must be about 50 nm in diameter: about a thousandth of a hair’s thickness. Figure 1 shows where these particles come from in the atmosphere.

Figure 1 – Where the particles in the atmosphere come from (left and center of the illustration) and how they are deposited (ie, back to the ground, right).

Figure 1 – Where the particles in the atmosphere come from (left and center of the illustration) and how they are deposited (ie, back to the ground, right).

Dust, sea salt particles and smoke particles come directly from the ground (blue arrows in the figure), while gas molecules can stick together and form particles (red arrows in the figure). If there are more particles in the sky, the resulting clouds bring back more sun rays back into space.

The illustration works from the original diagram of Jasper Kirby.

Looking from space, the clouds look like a bright white surface that returns some of the sunlight back to space. This fact plays an important role in regulating the amount of sunlight that reaches the ground. If there are few particles in the sky, fewer drops will be generated in each cloud and more light will reach the ground. This can significantly affect the temperature of the Earth because the clouds cover, on average, more than half of its surface.

When we pollute the atmosphere, for example with smoke particles (from factories, etc.), we change the number of particles in the sky. As a result, the clouds will contain smaller droplets and a larger quantity. It changes the brightness of the clouds: they return more sunlight back into space and less sunlight reaches the ground. This has reduced global warming by a quarter to half, caused by greenhouse gas emissions that absorb energy from the sun, such as carbon dioxide. Molecules composed of two atoms are more likely to become greenhouse gases, such as carbon dioxide, which we have experienced over the past century. Particle effects on earth temperature are uncertain. We need to understand these particles better to understand which warming (or cooling) are factors [1].

Create particles

Air is mostly composed of nitrogen and oxygen molecules, but there are many other molecules floating in the air. Some of the molecules that make up the air are more sticky than others (for a detailed explanation, see Box 1). Water is relatively sticky, but some other molecules are so sticky they can make particles by sticking directly to each other, without needing the surface the water molecules need to stick together. We refer to this process as an abstraction in the context of this article. This means the formation of particles in the sky using gas molecules that stick together. This process is also called “secondary particle formation” or “new particle formation”.

Box 1. Why some molecules stick more than others

Why do some of the molecules stick together?

In this article I described some of the molecules as more “sticky” than others. This means that certain molecules are pulled tightly together by electrical forces. All atoms contain a nucleus.


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