Australian Bushfires 2020: Procedure to Collect Ash Fallout

The measurement aim is to collect the full range of ash particle sizes and types precipitating from the air. Much of the material will be sub-micron in size. To get an idea of how small this is, a fine human hair is about 60 microns in diameter. The unaided eye cannot resolve individual particles but can see a lot of them when they form a surface film. Ideally, fallout is collected on a still day so wind does not preferentially remove the small particles from the sampling surface. For analysis only a small amount of ash is required, 1/2 a teaspoon is plenty. It is also important the sample is not contaminated, or as my sister put it, don't sneeze.

CASE 1: Light Ashfall

The fallout from the fires will most likely produce a light film of greyish ash. To capture these particles lay out about a metre of kitchen foil on a flat surface exposed to the sky. Depending on the rate of fallout you will need to leave the foil for between about an hour and a day. You have made a successful measurement if you can see a film that darkens the foil surface. It is a good idea to place some clean paper under the foil so the reverse side does not pick up any contamination. The corners of the foil may need to be weighed down with an appropriate item e.g. glass/metal paper weight. Use marker pen to write the word 'reverse' on the non-exposed side of the foil. After the measurement the foil should be folded in half so that the exposed side touches the exposed side. Continue folding (now it will just be reverse side contacting reverse) until the foil is about an A5 size (i.e. about the size of a medium envelope). The foil should then be sealed in a plastic zip lock bag or something similar.

CASE 2: Heavy Ashfall

In the unlikely event you experience heavy fallout then the best collection items are a clean glass or stainless steel bowl. After collection the ash sample can be transferred into a small plastic container. You may need to use a funnel to do this.

Samples can be sent to either
Dr Caroline Poulsen
School of Earth, Atmosphere and Environment
Monash University VIC 3800, Australia

or
Don Grainger
Clarendon Laboratory
Parks Road
Oxford OX1 3PU
UK

Please include the following information with the sample:

• name and email address (or other contact method),
• the location where the sample was collected,
• the date and time at the start of exposure,
• the date and time at the end of exposure,
• the area of the collecting surface.

If you collect more than one sample then please label them a, b, c etc.

Email me at r.grainger@physics.ox.ac.uk if you have any questions.

NOTES

• Moisture will affect the particles so do not allow the collecting surface to get wet.
• Fold the foil 'lightly', if you apply too much pressure you will crush the larger particles.
• For heavy ashfall, clean any item that you are going to use (e.g. basin, funnel, container) using water (preferably distilled or rain water) and allow the item to dry by evaporation.
• Avoid touching the collecting surface as much as possible.
• Taking some photos is a great idea too. Please send them to r.grainger@physics.ox.ac.uk.

Maintained by Don Grainger |