A brief introduction to aerosols..

Let’s skip the chit chat and go straight into post number three… Spray-cans will come to mind for many people when they first think of aerosols, but this term has a much more general meaning and plays an important role in climate science. Anything that has a suspension of liquid or solid in a gas is deemed an aerosol. In fact, a spray-can may actually contain hundreds of different individual aerosols.

A simple demonstration that shows the significance of aerosols in the atmosphere is the ‘cloud in a bottle’ trick. A trickle of water is added to an empty bottle and the cap put on. By just shaking and squeezing the bottle (simulating pressure changes that occur every day in the Earth’s atmosphere) no cloud is formed. However, if smoke is added, from a blown out match for example, and then the bottle squeezed, a small vapour cloud becomes visible – try it yourself or see the video of it below!

These tiny particles – aerosols – are necessary for clouds to form anywhere in the world. The photograph below shows how clouds have formed from aerosols released by ships.

Cloud formation using aerosols emitted from ships

Cloud formation using aerosols emitted from ships

Aerosol sources can be both natural and anthropogenic. The photo above is an example of industrial aerosol emissions but other major sources can include deserts (in the form of dust and sand) and from fires / biomass burning, which can be both natural and manmade, even tiny ice crystals can be classed as aerosols. One of the global climate models, Global Earth Observing System Model – Version 5 (GEOS-5) has simulated the emissions and transportation of all major aerosols from September 1st 2006 to March 17th 2007 and the video can be seen below. For a description of the colours see the figure description.

Summary copied directly from you tube link: “Dust (red) blows over the Saharan desert and interacts with two Atlantic tropical cyclones. Sea salt (blue) churned up from the ocean by surface winds is most prevalent along mid-latitude storm tracks and fronts in the Southern Ocean and within tropical cyclones. Organic and black carbon (green) burst from extensive biomass burning in South America and Africa. Sulphate (white) arises from three primary sources: fossil fuel emissions over Asia, Europe, and the United States; a persistently active volcano in Mozambique, Africa; and a large eruption from the Karthala Volcano on Grande Comore Island, Comoros, in January 2007.

Aerosols have both positive and negative radiative forcing effects (for more information on radiative forcing please read my first post! – An Introduction to Global Warming). The diagram below shoes the major contributors to global warming and whether they have a positive effect (a warming – coloured red) or negative effect (a cooling – coloured blue) on the Earth’s climate. The highlighted box shows the contribution from aersols – a very negative effect! However the black lines show how much of this estimation is uncertain. There is a large amount of research currently trying to reduce these uncertainty bars so we can be more sure of how much an overall effect aerosols have on our climate.

Global average radiative forcing estimates and ranges. Oringially produced by the IPCC.

Global average radiative forcing estimates and ranges. Originally produced by the IPCC.

There are two main ways aerosols effect our climate. The first is a ‘direct‘ way. I.e through re-radiating energy (warming the Earth) or reflecting incomming sun’s rays back out to space (cooling the Earth). Again, my first post explains this in more detail. The other way aerosols effect our climate is called the ‘indirect effect‘. As aerosols are needed as ‘seeds’ for clouds to form, an increase in aerosols can cause an increase in cloud number thus increasing the Albedo effect. When aerosols help form clouds they are referred to as ‘cloud condensation nuclei’ (CCN). The more CCN present the whiter the clouds can appear which further increases the albedo effect.

As you read this you may be thinking, the more aerosols present the better in the atmosphere as they have an overall cooling effect of climate however not all effects of aerosols are good. Aerosols can have a huge impact of air quality and atmospheric pollution. The recent smog events in Singapore (shown in the picture below) are thought to have occurred because of aerosols released from illegal biomass burning from Indonesia and travelling up to Singapore where they formed these smog clouds which can have severe health effects.

Comparison of Singapore skyline from Feb 2012 and June 2013. Image found on BBC News website.

Comparison of Singapore skyline from Feb 2012 and June 2013. Image originally from BBC News website.

Any questions or comments please write them below, or perhaps even a request for future posts?? Next time I plan to give a very brief overview of the history of the Earth’s temperature has changed over 65 millions years. They’ll be videos in that one as well!

Thanks for reading.

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8 thoughts on “A brief introduction to aerosols..

  1. Your blog is great Sarah! I’m enjoying reading it 🙂 I love this one in particular – I will use the ideas/videos for science club next year!! I am looking forward to the next post xx

  2. Pingback: 4.5 Billion Years of the Earth’s Temperature | MuchAdoAboutClimate

  3. Pingback: Key Figures From The IPCC’s AR5 Report | MuchAdoAboutClimate

  4. This is my first visit to your website. I’m very impressed. Nicely written, and from the few articles I’ve looked at so far, seems that you manage to keep away from the Denialist Game – and keep things to nice clean science explanation. Love it!

    Might I suggest that you embed a Post Archive list – so we can see what all you’ve posted at glance.

    Best wishes, Peter

  5. OK I see your post archive list, it’s on the home page.
    Keep posting your thoughts.
    For instance what about that Hoerling, Francis disagreement regarding changes to Jet Stream and north pole ice melt and extreme weather. That’s a timely important issue for people to get a better grasp of. Bet you could do the topic justice.

    • Dear Peter,
      Thank you for your compliments – it means a lot! I’m finding it hard to find the time to write posts right now (thesis deadline looming) but I will try to read into the jet stream variability more in the near future.
      Thank you,
      Sarah

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