Atmospheric Aerosols

Dr Ruhi Humphries, from Ocean and Atmospheres At CSIRO, tells us about what Atmospheric Aerosols are, why they are important and why they are studying them in Antarctica. He includes a "Make your own clouds" experiment at the end of the Page.. His Student Jack Simmons will be sampling for Antarctic aerosols on this mission.

What Are Aerosols?

We’re not talking aerosol cans here, we’re thinking about natural aerosols! Aerosols is just a fancy word for particles. In the atmosphere, these particles can be things like sea salt, dust and volcanic ash. The smaller and often more chemically complex particles are those which form when sticky (or oxidised) gases, such as sulfate, join together ( Figure 1), resulting in tiny particles that are 1000 times smaller than a red blood cell!

Figure 1: The process of particle formation and their interaction with sunlight!

The pictures below show some examples of naturally occurring aerosols including sea salt from wave breaking action (Figure 2), mineral dust from deserts and soil (Figure 3), and ash and sulfate from volcanos (Figure 4).

Figure 2: Sea spray from offshore winds. (

Figure 3: The Sydney Dust Storm, 23 Sept, 2009.

Figure 4: The Eyjafjallajökull Volcano, Iceland, caused major air travel shutdowns in 2010. 
Volcanos emit both ash and sulfate aerosol.

The video included here is a computer simulation run by NASA that shows the various types of aerosols that affect different parts of our globe and how they circulate with the weather patterns. We use these models regularly in our work to test our knowledge from data collected in the field and further understand the different forces in our environment.

Aerosols: Airborne particles in Earth's atmosphere

Aerosols in Antarctica.

Antarctica is so far from any other land that the air here is the cleanest in the world! This means that measurements taken in Europe, America, or even Australia are too polluted to really tell us anything about what’s happening in Antarctica. Because of these lower levels of pollution, the chemical reactions that take place in Antarctica are very different! So, to know how different, we have to go south on research vessels to measure it!

Surprisingly, in this area, there has only been one measurement campaign of aerosols before… ever! In 2012, we made measurements on Australia’s icebreaker, the RV Aurora Australis and found out that the number of aerosols in this area were 10 times more than what we thought! During this voyage, we’re trying to figure out why, and if it stays this high at different times of year. Understanding these factors will help us to understand the clouds and particles of the whole Antarctic and Southern Ocean region – and anywhere else as clean as that (think open oceans).

Figure 5: Air sampling in Antarctica using glass flasks.

Figure 6: The Aurora Australis, Australia’s icebreaker, was used to make the first measurements of aerosols in 2012. Left: nicknamed “the candy cane”, the aerosol inlet pulled air rapidly inside where it was measured for the number of aerosols. Middle: the “Ned Kelly inlet” provided protection from waves and cranes for the inlet which pulled air in for measuring various gases. Right: this instrument measures the amount of sunlight reaching it, and from this we can figure out how much aerosol and specific gases are in the atmosphere, and where they are!

But why are aerosols important?

Aerosols cool the planet and help keep it just the right temperature for us to live in. In fact, if we didn’t have aerosols, global warming would be going MUCH faster! Aerosols cool the planet by reflecting the light that is coming in from the sun. They do this in two ways: first, they reflect light themselves (the reason you can see the beam of a search light or torch, is that the aerosols are reflecting it back into your eye!); and secondly, they are the key to forming clouds (which if you’ve ever been on a plane looking down on a cloud, or watched a puffy white cloud pass over the sun on a hot day, you know are important to reducing the amount of sunlight reaching the ground)!

Figure 7: You can only see the path of a search light because aerosols are reflecting (or scattering) the light back into your eye!

Aerosols as the key to cloud formation – experiment time!

Without aerosols, clouds would simply not exist on earth. For cloud droplets to form without aerosols, you would need a relative humidity of over 300% (which is just not possible on earth).

But not all aerosols can act as seeds for clouds. They need to love water (be hydrophilic), and they must be the right size. Those that can be these seeds are known as “Cloud Condensation Nuclei”, or “CCN”.

You can see the effect of CCN at home by making your own cloud in a bottle! 

Get some parental supervision for this one, as you’ll be using matches (and maybe chemicals - i.e. nail polish remover).

You can follow this youtube video, or the (slightly simpler) instructions below.

Making Clouds in a Bottle

What you’ll need:

· Empty juice or soft drink bottle

· Water (or if you want even better clouds, use a very small amount nail polish remover)

· Matches

What to do:

1. Place a small amount of water (or nail polish remover) in the bottom of the bottle and put the lid on.

2. Squeeze and release the bottle a few times. This will help to make the water go to a vapour (or gas).

3. Take the lid off the bottle, then light a match, let it burn for a few seconds (until its burnt about 1/3 of the length of the match), then blow it out and while its still smoking, put the match into the bottle and put the lid on.

4. Now, squeeze and release the bottle again and you should see a cloud form!

What’s happening?

When you squeeze the bottle, the temperature of the air increases, which forces more water into the air. When you release it, the temperature decreases quickly and the amount of water vapour that the air can hold decreases with it. When there is no aerosol in there, the water vapour simply condenses back into the liquid at the bottom of the bottle. Once you add aerosol (after adding the match), the vapour has somewhere else to condense, so condenses onto the particles, and grows them into tiny cloud droplets! You’ve made your own cloud in a bottle.