PM10 vs Fallout Dust Monitoring: What’s the Difference and Which Method Do You Need?
When it comes to environmental dust monitoring, PM10 and fallout dust are not the same thing. Although both can be used to assess dust impacts from construction sites, mining operations, quarries, industrial facilities and other activities, they measure different characteristics of airborne dust.
Understanding the difference between PM10 monitoring and fallout dust monitoring is important when selecting the right dust monitoring equipment, developing an environmental monitoring programme, or demonstrating compliance with applicable air-quality requirements.
In this guide, we explain what PM10 and fallout dust are, how each is measured, what the results mean, and when you should use one method rather than the other.
What Is PM10?
PM10 refers to particulate matter with an aerodynamic diameter of approximately 10 micrometres or less. These particles are small enough to remain suspended in the air and can be inhaled. The US EPA describes PM10 as inhalable particles generally 10 micrometres and smaller.
PM10 monitoring therefore focuses on particles that are airborne at the time of measurement.
Typical sources of PM10 include:
- Construction and demolition activities
- Mining and quarrying
- Unpaved roads and vehicle movements
- Material handling and stockpiles
- Crushing and screening
- Wind erosion
- Industrial processes
- Agricultural activities
Because PM10 particles can remain suspended in the atmosphere, PM10 monitoring can provide information about short-term changes in airborne particulate concentrations.
How Is PM10 Measured?
PM10 is generally measured using equipment designed to draw a known volume of ambient air through a size-selective inlet and collect or measure the PM10 fraction.
Depending on the monitoring application, equipment can include:
- Continuous or real-time PM10 monitors
- Automatic particulate monitors
- Gravimetric PM10 samplers
- High-volume particulate samplers
- Portable dust monitors
Results are normally expressed as a mass concentration, such as micrograms per cubic metre (µg/m³).
This makes PM10 particularly useful when the objective is to understand airborne particulate concentrations and potential exposure.
What Is Fallout Dust?
Fallout dust, also known as dust deposition, deposited dust or settleable dust, refers to particulate matter that settles out of the atmosphere onto a surface.
Unlike PM10 monitoring, which measures particles suspended in the air, fallout dust monitoring measures the amount of material that has fallen onto a defined collection area over a specified period.
A typical dust deposition gauge uses a collection container and funnel positioned at a suitable monitoring location. Dust entering the gauge is collected over a defined sampling period and subsequently analysed.
The resulting measurement is generally reported as a deposition rate, for example:
g/m²/month
The New Zealand Ministry for the Environment describes deposited dust as dust that settles out of the air and notes that deposition measurements are commonly made using a collection jar or gauge over a fixed area and period.
PM10 vs Fallout Dust: The Key Difference
The simplest way to understand the difference is:
PM10 measures airborne particulate matter, while fallout dust measures particulate matter that settles from the air.
Feature PM10 Monitoring Fallout Dust Monitoring
What is measured? Airborne particles Deposited/settled particles
Particle focus Generally ≤10 µm aerodynamic diameter Primarily larger, settleable particles
Typical result µg/m³ g/m²/month or mg/m²/day
Sampling period Can be continuous, hourly or daily, Often monthly
Main purpose Assess airborne particulate concentrations Assess dust deposition and nuisance/amenity impacts
Typical equipment PM10 monitor or sampler Dust deposition/fallout gauge
Best suited to Air-quality and exposure assessment Dustfall and deposition assessment
It is important not to treat the two measurements as interchangeable.
Why Fallout Dust Does Not Equal PM10
One of the most common misunderstandings in dust monitoring is assuming that a fallout gauge measures PM10.
It does not.
A fallout or deposition gauge is designed to collect particles that settle from the atmosphere. Deposition equipment typically collects particles larger than approximately 10–20 micrometres, although there is no sharp particle-size cut-off and collection efficiency varies with particle size.
PM10 monitoring, on the other hand, specifically targets the inhalable fraction of particulate matter with an aerodynamic diameter of approximately 10 micrometres or less.
Consequently, a high fallout dust result does not automatically mean that PM10 concentrations are high, and a low fallout result does not necessarily mean that PM10 concentrations are low.
The two monitoring methods answer different environmental questions.
When Should You Use PM10 Monitoring?
PM10 monitoring is generally appropriate when you need to understand airborne particulate concentrations.
It may be appropriate for:
Construction sites
Earthworks, excavation, demolition, vehicle movements and material handling can generate airborne particulate matter. PM10 monitoring can help assess changes in ambient particulate concentrations around a site.
Mining and quarrying
Mining, crushing, blasting, haul roads and stockpiles can generate airborne dust. PM10 monitoring can form part of a broader air-quality monitoring programme.
Industrial facilities
Where an industrial process has the potential to generate fine airborne particulate matter, PM10 monitoring can help assess the concentration of particulate matter in surrounding air.
Environmental and air-quality studies
PM10 measurements can be used to establish baseline conditions, investigate potential impacts and assess trends over time.
Real-time monitoring can also provide much more immediate information than conventional deposition sampling, making it useful when investigating short-term dust events.
When Should You Use Fallout Dust Monitoring?
Fallout dust monitoring is particularly useful when the concern is dust deposition, nuisance dust or the amount of particulate material settling onto surrounding areas.
It can be useful around:
- Mines
- Quarries
- Construction projects
- Bulk material handling facilities
- Industrial sites
- Landfills
- Stockpiles
- Unpaved roads
- Residential areas potentially affected by dust
A major advantage of deposition monitoring is its simplicity and its ability to provide information about longer-term dust deposition trends. It can also allow the collected material to be analysed for its physical or chemical characteristics.
Fallout Dust Monitoring in South Africa
Fallout dust monitoring is particularly relevant in South African environmental monitoring programmes.
The SANS 1929:2005 fallout dust criteria referenced by Dust Monitoring Equipment include target and action levels based on dustfall averaged over 30 days. The referenced classifications include a long-term target of 300 mg/m²/day, residential and industrial action levels of 600 mg/m²/day and 1,200 mg/m²/day, respectively, and an alert threshold of 2,400 mg/m²/day.
However, the applicable monitoring requirements and limits for a particular site should always be confirmed against the relevant environmental authorisation, legislation, permit conditions, monitoring plan and current applicable standards.
How Does a Fallout Dust Gauge Work?
A typical fallout dust monitoring system consists of a collection container and funnel mounted at an appropriate height above ground level.
During the sampling period, airborne material that settles into the collection system is retained. At the end of the monitoring period, the sample is collected and processed to determine the amount of deposited material.
The result can then be compared with the applicable dustfall criteria.
The Australian/New Zealand deposited-matter method, AS/NZS 3580.10.1:2016, similarly specifies a gravimetric method for determining deposited particulate matter and provides an estimate of the mean surface concentration of deposited matter, typically over a one-month sampling period.
PM10 or Fallout Dust: Which One Is Better?
There is no universal answer because PM10 and fallout dust monitoring are designed for different purposes.
If your primary question is:
“How much inhalable particulate matter is suspended in the air?”
→ PM10 monitoring is likely to be the more appropriate method.
If your primary question is:
“How much dust is settling onto surrounding areas?”
→ Fallout dust monitoring is likely to be more appropriate.
For some projects, the best approach may be to use both methods.
Combining airborne particulate monitoring with dust deposition monitoring can provide a more complete picture of how a dust-generating activity affects the surrounding environment.
PM10 and Fallout Dust Can Complement Each Other
Using both methods can help distinguish between different types of dust impacts.
For example, a mining or construction site may produce relatively high airborne PM10 concentrations during a particular activity while also generating measurable dust deposition in surrounding areas.
Conversely, a site could experience significant deposited dust without necessarily producing correspondingly high PM10 concentrations at all times.
The difference is partly related to particle size, atmospheric conditions, wind speed, distance from the source and how long particles remain suspended.
This is why selecting monitoring equipment based on the monitoring objective is more important than simply choosing the most advanced or expensive instrument.
Choosing the Right Dust Monitoring Equipment
Before purchasing or installing dust monitoring equipment, consider the following questions:
1. What are you trying to measure?
Determine whether the objective is airborne PM10, deposited dust, total suspended particulate matter, or another particulate fraction.
2. What is the required sampling period?
Real-time PM10 instruments can provide rapid information about changes in airborne particulate concentrations, whereas fallout gauges are commonly used for longer sampling periods.
3. What standard applies?
Your monitoring programme should follow the applicable national or project-specific standard and any conditions contained in your environmental authorisation.
4. Where should the equipment be installed?
Monitoring location can have a major effect on results. Site selection should take account of prevailing winds, nearby structures, potential dust sources, sensitive receptors and the purpose of the monitoring programme.
5. Do you need real-time information?
If you need to identify dust events as they happen, a real-time PM10 monitor may be preferable to a conventional deposition gauge.
6. Do you need to assess dust nuisance or deposition?
If the primary concern is the amount of dust settling around a site, fallout dust monitoring may be the more appropriate approach.
The Bottom Line: PM10 vs Fallout Dust Monitoring
PM10 and fallout dust monitoring should not be viewed as competing methods. They measure different aspects of particulate pollution.
PM10 monitoring measures airborne inhalable particulate matter, making it useful for assessing concentrations of suspended particles in ambient air.
Fallout dust monitoring measures particulate matter that settles from the atmosphere, making it useful for assessing dust deposition and potential nuisance impacts.
For environmental monitoring programmes, the right method depends on the question you need the data to answer.
If you are unsure whether your project requires PM10 monitoring, fallout dust monitoring, or a combination of both, selecting equipment based on your regulatory requirements, monitoring objectives and site conditions is the best place to start.
Frequently Asked Questions
Is PM10 the same as fallout dust?
No. PM10 refers to airborne particulate matter approximately 10 micrometres or smaller, while fallout dust refers to particulate material that settles out of the atmosphere.
What unit is used for PM10?
PM10 concentration is commonly reported in micrograms per cubic metre (µg/m³).
What unit is used for fallout dust?
Fallout dust is commonly reported as a deposition rate, such as mg/m²/day or g/m²/month, depending on the applicable monitoring method and reporting requirements.
Can a fallout dust gauge measure PM10?
A conventional fallout dust gauge is not a PM10 monitor. Deposition gauges collect settling particulate matter and do not provide a direct measurement of airborne PM10 concentration.
How often are fallout dust gauges sampled?
Fallout dust is commonly collected over approximately 30 days, although the required sampling period should be determined by the applicable standard and monitoring programme. AS/NZS 3580.10.1:2016, for example, describes a typical one-month sampling period.
Should I monitor both PM10 and fallout dust?
For some projects, yes. Using both methods can provide complementary information about airborne particulate concentrations and dust deposition. The appropriate combination depends on the project’s environmental objectives and regulatory requirements.
Need Dust Monitoring Equipment?
Choosing the correct monitoring method is the first step toward obtaining useful, defensible dust monitoring data.
For PM10 monitoring equipment, fallout dust gauges and other environmental dust monitoring solutions, visit Dust Monitoring Equipment to explore equipment options for your monitoring requirements.
