Environmental Fallout Dust Monitoring Equipment and Devices

DustWatch CC - South Africa

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Fallout Dust Monitoring Practical and Theoretical Training - 1 or 2 day Training Course - Contact us for more information

Courses run in the 1st and 3rd week of each month as required.

The fallout dust monitoring section of the course aims to train the trainees so that they are able to do the following.




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Course Time Table for Two Day Dust Monitoring Equipment Training.

Day 1 

08:45        Registration
09:00        Welcome and Who is Who
09:15        Introduction to Environmental Monitoring - Fallout Dust
09:45        Discussion and Comments
10:00        What is precipitant Dust - Fallout Dust.
10:45        Discussion and Comments
11:00        Break
11:15        How to collect Fallout Dust
12:00        Discussion and comments
12:15        Particle Size and settling velocity.
13:00        Lunch
13:45        How to Calculate fallout dust results and Interpretation of the results.
14:30        Discussion and Comments
14:45        Trace Element Analysis and Fingerprinting
15:15        Break
15:30        Microscanning
16:00        General Discussion time and practical examples
17:00                End

Possible other topics for discussion:

               PM 10 discussion
               Relation of Fallout dust to PM10

Day 2 

09:00        Welcome and Names
09:15        Practical training of bucket changes and filtering procedure.
11:00        Break
11:15        Report writing and presentation options for the results will also be discussed. 
                Computer training as required.  Any aspects of computer training can be discussed.  Computer
                skills are important for performing tasks efficiently when using a computer.
13:00        Lunch
13:45        Access to our software for processing of the fallout dust data will also be included after the
                course.  This can be used to simplify the data collection and report writing and will also provide a
                database of the fallout dust levels over the years.
                If time allows, other aspects can be discussed to suit the specific requirements of the people
                being trained.
16:00        Discussion and Comments
16:30        Attendance Documentation

Course Handout - Updated August 2010


Looking up at the sky, we would never guess that our atmosphere contains between one and three billion tons of dust and other particles at any given time. Wind assists in keeping this dust airborne, but gravity wins most of the time, forcing the dust particles earthward, proving the old adage: what goes up, must come down.

Dust comes from many different sources. Some, like the byproducts of the combustion of fossil fuels, are man-made. Others
come from natural sources like sea-spray blowing off the ocean, or dust blowing in from the desert.  Dust comprises inorganic matter, such as sand particles, as well as a large amount of organic matter, including pollen, spores, moulds and viruses. These minute particles, ranging in size from around 100 micro metres (m) to a few nano metres (nm)3, invade our airspace every day, a part of life that we arent even aware of, except when we dust the furniture!


Aerodynamic diameter - the diameter of a spherical particle that has a density of 1g/cm3 and which has the same terminal settling velocity as the particle of interest.

Atmospheric dust Dust that is in the atmosphere.

Brownian Motion The continual random movement, due to molecular agitation, of fine particles suspended in a gas or a liquid.

d50 In a sample of dust the d50 diameter is the diameter above which fifty percent of the particles are larger and below which fifty percent of the particles are smaller.

Dry deposition The collection of precipitant dust during periods with no rainfall.

Export bucket The export bucket can be the North, South, East or West bucket that is closest to the dust sources. When the wind blows over the dust source towards the sampling location then the export bucket is open and dust from the dust source is collected in the bucket.

Fugitive dust Dust that is not emitted from a point source that can be easily defined such as stacks. Sources are open fields, travel-ways, stockpiles and process-buildings.

Meteorology the earth science dealing with phenomena of the atmosphere (especially weather).

Occult deposition Increasing particle size due to moisture that results in deposition due to increased mass of particle.

PM2 .5 Sampling of atmospheric dust where the aerodynamic d50 diameter is 2.5 m.

PM10 Sampling of atmospheric dust where the aerodynamic d50 diameter is 10 m.

Precipitant dust Any particulate matter that has an aerodynamic diameter below 100 m.

Total deposition The sum of wet and dry deposition. Occult deposition is also included.

Wet deposition The collection of precipitant dust and any soluble substances in the rainwater during periods of rainfall.

Definition of monitoring:

Keep the focus on using the tool to create awareness and achieve the objective of monitoring which is to create awareness of environmental pollution.

The design of a monitoring program must therefore have regard for the final use of the data before monitoring starts.

Environmental monitoring - The process of checking, observing, or keeping track of something for a specified period of time or at specified intervals.

Environmental monitoring must have a goal in mind and be linked to a problem or potential problem.

Keep it simple initially and then as the monitoring identifies problems, the results can be used to include more complicated results.  Reports should be easy to read and understand.

It is important to keep the big picture in focus when running a monitoring programme, while still maintaining high levels of quality control.

What is Precipitant Dust

Precipitant dust, as the word implies, is dust that precipitates or falls down. It refers to any particle with an aerodynamic diameter less than 100 m and precipitant dust is broadly defined as particulate that ranges in size up to 100 m in diameter. 

  1. Inhalable particulate mass is for those materials that are hazardous when deposited anywhere in the respiratory tract.  This is the particulate that will pass from the air into the nose or mouth and will travel up to the beginning of the throat.

  2. Thoracic Particulate mass is for those materials that are hazardous when deposited anywhere within the lung airways and the gas-exchange region.  This is the particulate that will pass through the throat and up to the small bronchiole.

  3. Respirable particulate mass is for those materials that are hazardous when deposited in the gas-exchange region.




Particle Aerodynamic Diameter (m)

Mass % Inhalable Particulate





















  The Mass % of Inhalable Dust that can be deposited.
The bold numbers in this table indicate how many of the particles with an aerodynamic diameter above 10 micron are inhaled into the body.  This provides information regarding the health implications of fallout dust, which is often regarded as benign.  If particles are breathed into the body then the contents of the dust can be absorbed into the body.


Particle Aerodynamic Diameter (m)

Mass % Thoracic Particulate

























Mass % that can be Deposited in the Lung Airways and the Gas-exchange Region
The bold numbers in this table indicate how many of the particles with an aerodynamic diameter above 10 micron are inhaled into the body.  This provides information regarding the health implications of fallout dust, which is often regarded as benign.  If particles are breathed into the body then the contents of the dust can be absorbed into the body.

The fall-out dust standards from STANDARDS SOUTH AFRICA are shown in the table below.  (SANS 1929:2005)


Dustfall (mg/m2/day) averaged over 30 days.

Permitted frequency of exceeding the levels.

Target long-term average


Long-term average (Annual)

Action residential


Three within any year, no two sequential months.

Action industrial


Three within any year, no two sequential months.

Alert threshold


None.  First time exceeded, triggers remediation and reporting to authorities.

How to collect fallout dust.

The present method used to establish precipitant dust levels is the ASTM (American Standard Test Method) D-1739 of 1998 Standard Method for Collection and Analysis for Dust Fall (Settleable particulates) 
While single open buckets partly-filled with a capture medium will accumulate all precipitating dust, this does not establish precipitant dust emanating from a given direction unless the bucket is closed to any dust from other directions. Such open buckets are also subject to inaccuracies due to wind turbulence within the buckets, lower air densities over the bucket and other factors.

The single-bucket precipitant dust collection method is a crude and nonspecific test method, but it is useful in the study of long term trends.

Image Courtesy of http://www.meted.ucar.edu/mesoprim/dust/print.htm



  Dust Storm Approaching Melbourne, Australia. - For more information see


How big is a micrometer?

A. One micrometer is 1/1 000 000 of a meter, or 1/1000 of a mm. For comparison, the thickness of a human hair ranges from 50 to 200 micrometers. The smallest particle discernible by the human eye is about 10 micrometers. - Taken From http://www.meted.ucar.edu/mesoprim/dust/print.htm

http://www.meted.ucar.edu/mesoprim/dust/aeolian.htm - Wind-Driven Movement of Sand and Dust particles by Creep, Saltation, and Suspension.  Some of these are collected in dust monitoring equipment


http://www.meted.ucar.edu - Register and get access to their material.  An excellent resource.

Initially keep it simple and then if required go to more complex scenarios. 

Carriage of Airborne Particulates
Carriage of airborne pariculates.  Fallout dust dynamics for different particle sizes.

With factors like particulate density and shape playing a major part in the distance that the particle will travel, the above table is only an indication based on testwork with tracer dust.  The height to which particulate is lifted depends on air turbulence, temperatures, humidity, density and thermals which can be encountered.  Vegetation and Bush can impede and capture larger particulates.

does not impede travel of dust unless close to source of dust

Trees will arrest greater than 50 micrometre or 50 micron dust particulates up to a height of 10 metres

Bushes will arrest greater than 80 micrometres or 80 micron particulates up to a height above the ground of 3 metres.

Bushes will arrest greater than 80 micrometres or 80 micron particulates.





How to Calculate fallout dust Results and Interpretation.

1.0               CALCULATIONS

        The cross-sectional area of the buckets is a standard constant in all of the calculations representing the area over which fall-out collection has been made:  = 0.02545m2

         The actual mass collected is derived by subtraction of the mass of the filter (mass1) from the combined mass of the filter and filtrate (mass2):
 Mass2 mass1 = collected mass of dust sample 

         All units should be expressed in milligrams and the value of milligram/square metre/day derived from the formula:
 Fall-out rate (mg/m2/day) = (collected mass x 1)/(0.02545 X days)


         Generally finer suspended dust (2.5m > 5m) will remain airborne almost indefinitely due to the dynamic nature of the air currents and thermal activities on any given day, even if there is no wind at all.  A rapid increase in humidity together with an absence of wind will result in precipitation of less than 5 micron particulate. 

         Particulate larger than about 5m will settle on a very still day and this material is collected within the DustWatch buckets in varying amounts depending on the wind velocities. 

         Particulate of a size about 0.5mm carried by high wind velocities will not be collected within the buckets due to the aerodynamic shape and wind screen effect of the selector disk.  This acts much like the wing of an aircraft, which produces a high-pressure area below the disk, keeping the gritty particulate from falling into the buckets.  The disk optimum efficiency occurs at wind velocities exceeding 2.0m/s.   At velocities below 3.0 m/s no particulate of this size is lifted higher than a maximum of about 2.0m. 

        Once the wind changes direction the particulate starts precipitating and this gets captured in the buckets.  We thus note that no dust gets captured during very windy conditions but actually when the wind drops.   Once the wind changes, the maximum precipitation rate is reached when the air mass movement is totally arrested and then starts to move in the opposite direction.

Unit Location Options
Fallout dust monitoring unit location options

Results Achieved - Linear Function

Source Export Dust and Ambient Import
A.  Direction Export from Source
B.  Ambient Import

Cross Contamination - Two Stockpile
A. Direct A Export
B.  Direct B Export

Nett Export / Ambient Import
Nett Export North = A1 - C
Nett Export South = A - B
Ambient Import = C and B (S and N)

Fall-out Quantification
Fall-out at x metres = A3
Fall-out at (x+y) metres = A2
Fall-out at (x+y+z) metres = A1

Village Nett Import
Import from North = B
Import from South = A
+ Import from East and West = C and D

Source Export with Ambient Import From 3 Directions
A.  Direct Export From Source
B.  Opposing Ambient Import and Import From Other Directions C and D

Nett Export / Ambient Import - 4 Directions
Nett Export North - A1 - B1
Nett Export South - A - B
Ambient Import = B1 and B (S & N)
Ambient Import = C - Checks C & D - Checks D (East and West)




Very often there is a necessity to know more than the mere proportions of various chemical elements within a sample, especially when detailed fingerprinting has to be undertaken.   Under these circumstances or where a high natural radiation level exists it is important to view trace elements like the following:

The analysis lends itself ideally to fingerprinting for a suite of some 40 60 elements depending on the composition of the dust.



The carrying out of a routine microscopic examination offers a valuable continuous check for any sign of fibres of a mineral nature as well as giving an indication of the amount of organics within the sample.  While very detailed examinations require specialised knowledge and techniques, the type of examination carried out here can be extremely valuable in offering an insight into the collected dust.


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  Last modified: July 18, 2018

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