Hygroscopic Condensation Nuclei | Cloud, Rain formation

This article talks about – “how condensation takes place”. A very simple form of condensation is – get a bottle of cold water from the fridge, keep it outside for sometime, you will see water droplets starts to form on the outer surface of the bottle. So what do you think is happening?

Since the bottle has cold water inside, naturally the bottle itself will be cold. Now we know that there is moisture in the air, in other words humidity. If we look at the outer surface of the bottle very closely, air molecules in the surrounding constantly hits the outer surface of the bottle from all direction (omnidirection). Since the bottle is cool, the air right next to the bottle gets colder. That means the air which already has moisture cannot hold anymore water when it is closer to the surface of the bottle. And that’s how moisture or water vapour transforms into liquid droplets (gas turns into liquid).

Now this is a tiny example, but the process is same in the formation of clouds and rainfall. The next interesting question to think about is – what is there inside a water droplet? Or in other words, what is holding the water together in the shape of a drop?

It is because of Hygroscopic Condensation Nuclei. I know it’s a long terminology, but its fairly easy to understand. If you study particle physics, to understand the substructure of a material in decreasing form (bigger to smaller).

1. At first we have a solid block – this could be any object that you see around you.
2. Then there are molecules that together give structure to the solid block.
3. If we go further, molecules are formed when two or more atoms are combined together. An atom is the smallest unit of matter. Inside an atom you’ll find subatomic particles like proton, electron, and neutron.
4. A combination of these sub-automatic particles form nucleus. Nucleus is the center of an atom. And the plural form of nucleus is nuclei.

Basically everything that we see around us comes down to nuclei. Likewise, when water droplets are formed during condensation, there is a central nuclei that holds the water together in the form of a drop.

So what is this nuclei? Well, these are nothing but extremely tiny particles of dust, smoke and salt of the sea and ocean. There is a term given to it – aerosol. These aerosol has an amazing property of attracting and holding water molecules from the surrounding environment. That’s how the term hygroscopic comes into the picture.

So if at all anyone asks you – what is there inside a water droplet? Or what is it that holds the water together in the shape of a drop? Now you should be able to say that there are tiny particles of dust, smoke and salt which have the property to absorb water molecules from the surrounding environment.