Guidance

Monitoring ambient air: particulate matter

A summary of the main methods you should use to monitor for particulate matter in ambient air.

• From: Environment Agency
• Published: 10 September 2024

Applies to England

We use both the terms particulate matter (PM) and dust in this document as they are generally interchangeable.

Airborne PM is all around us and has a wide variety of sources. These sources can be natural, for example:

• sea spray
• entrained dust
• fires
• Saharan dust

Or the sources can be human activities, for example:

• road transport
• combustion
• industry
• minerals extraction
• construction

Particulate matter suspended in the air is a complex mixture of solid and liquid particles that come from local and regional sources, and sources in other countries (transboundary sources).

The general term for suspended particulate matter is an aerosol. If there are liquid particles use the terms mist or cloud. If the particles are solid, they are a smoke or dust.

This mixture can include:

• elemental and organic carbon (including complex organic chemicals)
• sulfate
• nitrate
• ammonium
• sodium chloride
• mineral dust
• water
• series of metals

Some of these particles are ‘primary particulates’. This means they are emitted directly into the air from a source such as an engine or an industrial process.

Others are ‘secondary particulates’. These are formed from reactions between other pollutants (for example, nitrogen dioxide, sulfur dioxide and ammonia) already in the air. They mainly consist of aerosols of ammonium sulfate and nitrate salts.

Secondary PM makes a significant contribution to the overall atmospheric loading of particulates. PM also originates from outside the local area, with regional and transboundary pollution usually being the main source of background levels.

Dust and its journey from source to receptor

To understand how to monitor dust and PM around regulated industrial and waste facilities, you must understand how it behaves in the air.

An emission source will generate dust and release it to air, for example when waste is tipped from a lorry on to a stockpile. Once the dust is in the air (termed ‘suspended PM’) it will spread out from the source and the wind will carry it away from the site.

The impacts of dust released from a non-elevated source (that is one close to the ground) will decrease with distance, because of dispersion and dilution.

For elevated sources such as stacks, the maximum ground level concentration will be some distance from the source, at the point where the plume intersects the ground.

Dust flux

The dust flux is the quantity of particles travelling past a particular location. You can measure this by placing a sampling device (a dust flux gauge) in the vertical plane. This captures the dust as it passes by in a direction approximately parallel to the ground.

The dust flux is often expressed in units of mass per unit area in the vertical plane per unit time. For example, milligrams per square metre per day (mg/m²/day). But you can also measure metrics other than mass (for example staining effect).

If you locate the flux gauge on the site perimeter, then the flux that you measure is the fugitive dust release rate across the site boundary.

Dustfall

When wind carries a ‘parcel’ of particles in air away from the source, some of the particles settle out of the air – this is the dustfall. The larger dust particles deposit almost immediately close to the source (and quite possibly within the site boundary). Finer particles fall out of the air only after some considerable time and distance.

You can measure the dustfall rate at a particular point by placing a dust gauge in the horizontal plane to collect the particles as they deposit out of the air and on to the surface. Only the very largest and densest particles fall at an angle approaching the vertical. Most particles deposit at a very shallow angle approaching the horizontal. Even so, gauges with upward-facing collecting surfaces will collect a different fraction of particulate matter from those with vertical collection surfaces, such as the directional flux gauge.

Dustfall rate (also known as the ‘dust deposition rate’) is often expressed in units of mass per unit area in the horizontal plane per unit time. For example, mg/m²/day. But, as with dust flux, it is also possible to use parameters other than mass as an indication of the quantity of dust. For example, dust coverage, staining effect, and loss in surface reflectance.

Suspended PM

There is an inverse relationship between dust flux and dust deposition. As dust falls out of the air during its journey, the mass of dust remaining airborne and continuing to travel away from the source must reduce by the same amount. This fraction of dust, that is still suspended in the air, becomes dispersed by the wind, and diluted in an ever-greater volume of air. This means the concentration of the suspended PM falls as the dust cloud moves downwind.

You can measure this concentration of suspended PM at any location by extracting a known volume of air into a sampler and estimating the mass of the particles it contained. The concentration of suspended PM is therefore normally given in units of mass per unit volume. For example, micrograms per cubic metre (µg/m³). You can also measure PM concentration as the number (rather than mass) of particles per unit volume of air. However, this is not common as there are no standards or adopted criteria against which to judge significance.

Receptors

For the particles to have an impact, they must reach a receptor. Receptors include:

• people and their properties (users of the adjacent land)
• materials
• plants and animals
• soils
• water bodies

Different receptors vary in their sensitivity to dust and IAQM guidance gives several classifications of sensitivity to dust. See their guidance ‘Air Quality Monitoring in the Vicinity of Demolition and Construction Sites 2018’.

The impact at a receptor will depend on how much dust there is, and the sensitivity of that receptor to dust. For dust, the most common types of exposure are:

• from inhalation of particles, potentially leading to health effects
• annoyance or nuisance

People can also be exposed to dust through the:

• oral route (ingestion) – directly, or indirectly from food grown or reared nearby
• dermal route (skin contact)

The importance of particle size

Particles suspended in air can vary from the extremely small (in the nanometre size range) up to around 1mm.

This is despite the standard definition of dust (BS ISO 4225:2020 Air quality – General aspects – Vocabulary) saying:

• particulate matter means 1 to 75µm in diameter
• grit means particles greater than 75µm in diameter

Particle deposition

Suspended particles are normally deposited. The rate of deposition depends largely on the size of the particle and its density. The size of a particle and its density influence:

• the aerodynamic and gravitational effects that determine the distance it travels
• how long it stays suspended in air before it settles on to a surface

Larger particles deposit out of the air within a short time and distance, whilst finer particles remain suspended in the air for considerably longer. For example:

• particles with diameters greater than 50µm tend to deposit quickly
• particles with diameters less than 10µm have an extremely small deposition rate in comparison

For more information on this, see: Department of the Environment, ‘The Environmental Effects of Dust from Surface Mineral Workings’, ISBN 0 11 753186 3 (1995). 

People can breathe in suspended particles that are up to 10µm aerodynamic diameter (PM₁₀).The Air Quality Expert Group’s (AQEG) 2005 report Particulate Matter in the United Kingdom defines PM₁₀ as ‘airborne particulate matter passing a sampling inlet with a 50% efficiency cut-off at 10µm aerodynamic diameter and which transmits particles of below this size’.

The convenient simplification usually made is that:

• the dust fraction, comprising particles larger than 10µm diameter, deposits out from the air within a few hundred metres to a kilometre or so of the source
• those particles suspended in the atmosphere for any significant length of time (and therefore distance) comprise the PM₁₀ fraction

For more information on this, see: Office of Deputy Prime Minister, Minerals Policy Statement 2 (MPS2), Annex 1: Dust, (2005).

Deposited dust is also sometimes called ‘amenity dust’ or ‘nuisance dust’, with the term nuisance applied in the general sense rather than the specific legal definition. Deposited dust on a Frisbee gauge (or any other horizontal gauge), is for simplicity often considered to be the larger fraction (greater than PM₁₀). This is because only large particles are usually visible to the naked eye. However, smaller particles (PM₁₀) will also be present in the deposited dust, even though these are unlikely to cause nuisance effects.

Dustfall and suspended particulates

The distinction between suspended particulate matter and deposited dust determines the potential adverse effects that can occur.

For dustfall, you can divide the effects of deposited dust into the following.

1. The effects of the bulk property of the dust, irrespective of its composition, to cause nuisance by its prevalence or its capacity to soil surfaces. (For example, a car, windowsill, laundry, buildings.) The bulk smothering effect of dust can also, potentially, have impacts on vegetation and invertebrates.

2. The effects of the deposited dust resulting from the toxic or corrosive nature of the elements (for example, metals) and compounds of its composition. This may lead to impacts on soils and vegetation and add by ingestion to people’s (and animals) total exposure to the substances on top of what they receive from inhalation of the PM₁₀ fraction.

For suspended particulates, the PM₁₀ particles are small enough to breathe in and so can potentially impact on people’s health. So, when we monitor suspended dust, we are normally interested in measuring the PM₁₀ fraction rather than total particulate matter (TPM) that contains the larger suspended dust particles as well.

Measurements of PM₁₀ concentrations in the air will include the PM_2.5 sub-set (the fine fraction of particulates that is less than 2.5µm aerodynamic diameter). However, you may also report PM_2.5 concentrations separately, and this metric has taken on an increased importance as the combustion-derived particles in this size range may have the greatest adverse impact on human health. You can breathe in all PM₁₀, but not all travels as far down as the lungs. Part of it does though, the most significant sub-fraction of PM₁₀ from this perspective being the PM_2.5 range (particles with a diameter smaller than 2.5 µm), which can travel deep into the lungs.

Ultrafine particles

It is not commonplace to measure ultrafine particles (<0.1 µm diameter) or nanoparticles and the current official advice of UK Health & Security Agency (formerly Public Health England) (The Impact on Health of Emissions to Air from Municipal Waste Incinerators) is that the health effects of these are adequately covered by the Air Quality Standards set for PM₁₀ and PM_2.5. Similarly, it is not commonplace to routinely monitor particle number concentration (particles per unit volume of air). The advice notes that:

• we do not know how to interpret measurement of number concentrations of particles in health terms
• no generally accepted coefficients that allow the use of number concentrations in impact calculations are yet defined
• no one defines Air Quality Standards in number concentration terms

Work in this area is developing.

We can categorise suspended PM size ranges from a health perspective. The human breathing system has evolved to filter out large particles at an early stage, and the proportion of particles reaching the lungs depends strongly on the particle size.

The American Conference of Government Industrial Hygienists (ACGIH), the International Standards Organisation (ISO), and the COMEAP/HPA Handbook on Air Pollution and Health have defined particle fractions on the following basis.

Inhalable fraction

The mass fraction of total suspended particles inhaled through the nose and/or mouth; there is no sharp cut-off point in terms of particle size for particles that people can inhale, but the nose traps particles greater than 15 µm and they go no further. However, the proportion of dust that can penetrate further depends on the particle sizes.

Thoracic fraction

This is the mass fraction of inhaled particles that penetrates the respiratory system beyond the larynx. It has a median diameter of 10 µm, broadly corresponding to what we call the PM₁₀ fraction.

Respirable

The mass fraction of total suspended particles that penetrates to the unciliated regions of the lung (cilia sweep mucus and dirt out of the lungs and are present in the ‘conducting zone’ that routes the air, comprising the trachea, the bronchi, the bronchioles, and the terminal bronchioles). This fraction has a median diameter of 4 µm.

‘High-risk’ respirable

The mass fraction of total suspended particles that penetrates to the ciliated regions of the lung (this is the respiratory zone, comprising the respiratory bronchioles, the alveolar ducts, and the alveoli). This fraction has a median diameter of 2.5 µm, broadly corresponding to the PM_2.5 fraction.

Ultrafine particles that are <20 nm (<0.02 µm) that can reach the alveoli

As a size range, AQEG (Particulate Matter in the United Kingdom) defines ultrafine particles (PM0.1) as <100 nm and nanoparticles as <50 nm.

Emerging scientific evidence

The emerging scientific evidence is that the most biologically active (and potentially damaging) component of most particulates we are exposed to is the soot (elemental, or black, carbon) from road traffic, particularly diesel engines, which can make up a considerable proportion of the PM₁₀, and especially the PM_2.5, in many urban areas.

The monitoring techniques and the compliance limits of deposited dust and suspended PM are different because of the different effects they have.

Sources and types of particulate matter around regulated facilities

Not all the airborne or deposited particulate matter around a regulated facility will be from the facility itself. A proportion probably will be, but this process contribution (PC) superimposes on top of the underlying ambient background contribution (BC). The total environmental level (the sum of PC + BC) is what is important in terms of exposure. But in terms of environmental regulation there will tend to be a strong focus on the PC from regulated facilities.

Understanding the ambient background

An understanding of the make-up of the underlying ambient background is necessary. Also, a knowledge of the likely types of particulates added on top of this by different operations. If you are to design a successful monitoring scheme that will enable you to draw useful conclusions on the impact of the site.

High background levels may leave limited headroom for additional emissions from future developments in the area. This has implications for the setting of appropriate action levels for compliance monitoring purposes. Background levels are also important in considering enforcement action: though there may be no argument about the adverse environmental or health impacts of elevated levels of particulate around a site. If it is largely because of background levels, then an operator may be limited in their ability to influence this. You will need to take care in these circumstances to make sure you follow a proportionate approach.

Large particles (suspended PM greater than 10 µm) generally do not travel far, so it is mainly local sources of these that usually contribute to the ambient background concentrations in the air and to dustfall levels. The chemical and physical composition of the larger particles tends to show a strong dependence on the characteristics of the local sources.

The picture is different for PM₁₀ and the fine subset of this, PM_2.5. The underlying ambient background concentrations in each area depend on:

• local emission sources
• regional pollution
• pollution from more remote sources brought in on incoming air mass

Urban background

These can have quite different chemical compositions. In urban areas the predominant primary local source is road traffic, including re-suspended dust from road surfaces, particles from brake and tyre wear, and diesel engine exhausts. Diesel engine exhausts contain highly biologically reactive sooty particles known as black carbon. They may be responsible for much of the observed adverse health effects of these particle size ranges.

Rural background

In rural areas, the background PM concentrations from local sources may be from agriculture, quarrying or mining. These primary local particles are additional to an underlying regional level of PM, a substantial proportion of which is transboundary. This may arise from direct emissions from traffic, industry, and agriculture, but much of this long-range pollution is secondary PM. This forms from gases, such as sulfur dioxide and ammonia during their journey on winds from their points of origin. Long-range particulate pollution tends to have a large proportion of PM_2.5 and is usually high in volatile PM, sulfate and nitrate. You can find further information on ambient background PM in the AQEG report, Particulate Matter in the United Kingdom and the SNIFFER report, PM_2.5 in the UK (2010).

Monitoring dust deposited from air (dustfall)

Here we look at methods for measuring dustfall and guideline limits.

Mass deposition rate and soiling rate

People experience nuisance from dustfall in several different ways, sometimes in combination. They may be annoyed about the amount of dust, or by the soiling that it causes to their property and belongings, such as car paintwork, windowsills, or laundry.

One way to gauge the size of this nuisance is to measure the community response directly. For example, monitoring levels of complaints or asking people with surveys and questionnaires. The other way is to try and measure quantitatively some physical feature of the dustfall that correlates with the nuisance effect. The following measures are in use:

• the amount and regularity of nuisance dust
• the amount of soiling of property and belongings

Further information is provided in the index of methods.

The mass of dust relates to the amount of dust. The mass of dust is easily and reproducibly measured, so you can use it as a measure of nuisance caused by dust.

You should monitor nuisance dustfall at receptors to gauge the nuisance dust impact at those locations. If this is not practicable, locate the dustfall samplers on land under the control of the site operator, for example, just inside the site perimeter. In such cases, the assumption is usually made that the results can represent a worst-case estimate of the impact at receptors, since dustfall generally decreases with distance.

The dustfall monitoring approaches of mass deposition rate and soiling rate are complementary. Sometimes one will be more appropriate to a particular site, process emission or receptor than the other. But monitoring both may sometimes provide a more complete measure of the nuisance impact.

For example, monitoring Effective Area Coverage (%EAC) is best suited for monitoring of dark coloured dusts. You can compare results with an agreed nuisance limit.

Another example is low density material, such as woodchip. The normal custom and practice mass deposition rate guideline of 200 mg/m³/day does not properly reflect the nuisance effects from these materials. To use mass deposition rate as a measure of nuisance from such low-density materials, you should derive a bespoke benchmark limit. This is done by correlating observed dustfall rates with complaints data or community responses. Such a study may be able to use monitoring and complaints data that the site has already collected.

The alternative approach would be to use a metric of nuisance based on the prevalence of the dust rather than its mass, such as measuring actual area coverage (%AAC/day). Unfortunately, no universally accepted nuisance benchmark limit yet exists for dustfall as %AAC/day. Further research and study is needed to establish one by correlating observed measurements with complaints data (complaints to all bodies, not just to the operator) or community responses.

All the nuisance dustfall monitoring methods are manual techniques (no automatic methods being available). We provide a brief description of each approach in section 5.

All the above dustfall monitoring techniques use horizontal samplers that are omni- directional and give no information on the direction the dust has come from. If you need to distinguish dust from different directions, then you may complement the dustfall samplers (this will increase the cost) with vertical dust flux gauges. These are ‘directional’, they allow you to distinguish the amounts of dust coming from different quadrants. Note that such vertical dust gauges do not provide measures of dustfall in the conventional sense. They can provide an estimate of the dust deposition on a vertical surface (such as a building façade or laundry). This may be the issue of concern on some occasions.

Further analysis of deposited dust

Here are some methods for further investigations of dust.

Loss on ignition

You can estimate the organic content of a dust sample by determining the loss in mass of the dried dust sample after ignition in a crucible at high temperature. The fraction that remains is non-organic in nature (although losses can also occur from carbonates and hydrates).

Chemical analysis

You can analyse a dust sample (for example collected using a Frisbee gauge) to give a comprehensive compositional breakdown of the deposited dust.

Chemical analysis is valuable in quantifying the levels of specific contaminants in the deposited dust. For example, at waste facilities, the most likely requirement to chemically analyse the collected samples of deposited dust is to determine the levels of heavy metals and metalloids, such as:

• cadmium
• thallium
• mercury
• antimony
• arsenic
• lead
• chromium
• cobalt
• copper
• manganese
• nickel
• vanadium

Sample preparation involves acidifying the filtered solid deposited matter from the Frisbee gauge and its collection bottle, and the filtrate. The analysis of the digested metals content of the combined solution will be typically by one of the following:

• inductively coupled plasma - optical emission spectrometry (ICP-OES)
• inductively coupled plasma - mass spectrometry (ICP-MS)
• cold vapour - atomic fluorescence spectrometry (CV-AFS)

Calculate the deposition rate for each metal in units of mg/m²/day² from the amount of metal collected, the sampling area of the Frisbee gauge, and the number of days of exposure of the gauge.

Particle identification

You can examine the optical and morphological properties of individual particles by:

• light microscopy (conventional reflected light microscopy
• polarised light microscopy, or dispersion staining)
• electron microscopy (transmission electron microscopy, TEM, and scanning electron microscopy, SEM)

You can determine the chemical composition of the individual particles by advanced analytical techniques such as:

• electron diffraction,
• x-ray fluorescence (XRF) spectroscopy
• energy dispersive analysis by x-ray (EDAX)
• electron or ion probe microanalysis.

Dust flux monitoring technique

Dust flux monitoring is best suited for assessing dust releases across a site boundary.

Dust flux is always sampled with a collection device positioned in the vertical plane to intercept dust as it travels nominally parallel to the ground. You can use different collection devices and different analysis stages. Further information is provided in the index of methods.

Guideline limits for dust flux

There are difficulties in setting a limit value for the rate of nuisance dust travelling past a location (dust flux) for the following reasons:

1. An acceptable flux past a particular location will depend upon what the subsequent impact will be when the dust settles out of the air as dustfall, at some point downwind, at a sensitive receptor.

2. Locate flux gauges at some point between the source and the receptor, preferably at the site boundary. When a flux gauge is located on the site perimeter, it gives a measure of the site’s fugitive dust emission rate across its boundary.

3. The dust flux from one site may have a different significance to the dust flux at another site, dependent on the pathways (for example, distance and direction) to the nearest receptors and the sensitivities of those receptors.

Consequently, there are no agreed numerical standards for dust flux.

To set an appropriate numerical compliance limit for dust emission rates across a site boundary, consider the level of emission likely to cause an adverse impact at receptors. To set a risk-based limit, correlate the levels of dust emissions across the site boundary (the dust flux) with the level of impact at the nearest sensitive receptors. For existing sites do this either:

• qualitatively (for example, by correlating measured dust flux with community responses such as complaints frequency or the results of dust diaries)
• quantitatively (for example, by correlating measured dust flux with dust deposition rates monitored at receptors)

Operators should record complaints data as a matter of routine. This can provide operators with data to make a site-specific correlation with dust flux, to establish a non-compliant threshold.

In the absence of a site-specific dust emission rate limit, you can compare the boundary dust flux to the background dust flux. This provides a good indication of the significance of the emission rate across a boundary. You can compare between the measured dust flux from the quadrant facing the site (the dust emission from the site boundary) with the dust fluxes from other directions. This will give an estimate of the magnitude of the cross-boundary emissions as a multiple of the normal background dust flux.

You can also use vertically orientated flux gauges to determine the relative intensities of dust flux from different directions. This enables you to understand the relative importance of dust sources from different directions. This means you can use vertically orientated flux gauges as a management tool to monitor the effectiveness of your dust controls. Also, you can separate the relative contribution of your site from the interference of sources from other directions.

Visual assessment of dust emissions

Operators may need to make regular (for example, daily) subjective visual assessments of dust emissions across the site boundary as part of their routine walkover inspections. Visual observations of dust emissions are affected by:

• the subjective opinion of the observer
• his visual acuity and powers of observation
• the environmental conditions at the time (such as light and wind conditions)

The assessment criteria may be similarly subjective: for instance, a permit may state that “there shall be no visible dust emissions”.

Despite its subjective nature, this simple, cheap, and easy to implement assessment approach has the significant advantage of providing instantaneous information on problems. For example, it may be possible to directly observe the source of the dust emission, such as a particular stockpile of material. This allows the taking of rapid actions to deal with the problem.

Bioaerosols

Bioaerosols are microscopic airborne particles or droplets of biological origin. The sizes of the individual particles vary from fractions of a micron up 30 µm or more. But many tend to form larger clumps or agglomerations, or to attach to inert dust particles. These biological aerosols are complex and may include:

• viruses
• bacteria (including actinomycetes)
• fungal spores
• enzymes
• endotoxins
• mycotoxins and glucans
• dust mites
• protozoa
• fragments of plant material
• shed animal debris (such as skin cells and hair)

Bioaerosols consist of viable components (that is living organisms and cells) and non-viable components that were part of an organism (for example cell walls).

Bioaerosols arise widely throughout the waste industry including:

• waste collection
• materials recovery facilities
• mechanical biological treatment facilities
• composting
• storage of waste material prior to incineration

Increased activity levels and the agitation of material such as turning of windrows during composting and the shredding of material can lead to increased levels of bioaerosol production.

The composting process relies on the growth and activity of micro- organisms. Different groups of micro-organisms predominate at different phases of the composting process according to how well they adapt to specific conditions such as temperature. Cellular waste products such as endotoxins and glucans are also present during composting. Composting relies on turning the compost regularly to increase aeration and maintain optimum composting activity by increasing porosity of the windrow pile. It is during the agitation of the material when the warm buoyant air rises from the windrow that elevated numbers of bioaerosols are released and dispersed downwind. This has caused concerns over the impact of bioaerosols on the public living around such facilities. However, there is the potential to reduce exposure to bioaerosols from such facilities by the implementation of good practice and having adequate control measures in place to minimise bioaerosol release.

A study by the Health and Safety Executive (report RR786) confirmed that large concentrations of bacteria (including actinomycetes) and fungi, and to a lesser extent endotoxin, are found close to the source of composting activities such as windrow turning. But there was little evidence of a major contribution to the overall bioaerosol burden by 250 metres from such activities.

A significant exposure to bioaerosols could be associated with different adverse health effects such as increased risk of respiratory illness and possibly gastrointestinal symptoms and fatigue. The type of effect is dependent on the species present and the associated exposure level. At the present time we cannot fully quantify the true significance of the health impact due to a lack of dose response data for individual components. For more details on health effects refer to the IOM/Defra review (Searl A (2010) Exposure- response relationships for bioaerosol emissions from waste treatment processes. Defra Project WR0606).

The Environment Agency has more guidance on environmental monitoring of bioaerosols at regulated facilities.

Asbestos

At some waste facilities, such as landfill sites, particulate matter in the form of fibres may be encountered.

This includes materials such as asbestos and man-made mineral fibres (MMMFs). Asbestos waste must be deposited in a landfill for hazardous waste, a site designed to accept asbestos only or in a separate cell in a landfill for non-hazardous waste, but only if the cell is sufficiently self-contained and the design provides a physical separation and isolates the asbestos so that it remains undisturbed (Council Directive 1999/31/EC of 26 April 1999 on the landfill of waste.)  To prevent the uncontrolled release of asbestos fibres there must be no drilling through asbestos cells.

Asbestos legacy

There is also the legacy of asbestos and MMMF being released to air from contaminated land. We have conducted trials with the HSE to support development of guidance for assessing the risks from asbestos in contaminated soils. See the Asbestos in Soil report on this work. We are now also seeing a small number of contaminated land remediation projects involving treatment of soils contaminated with asbestos away from the site.

The epidemiological risk implications of fibres are due, in part, to their long, thin structure (aspect ratio) and, especially for asbestos fibres, their propensity to break down into ever finer, sharp fibres. The main health impacts from asbestos are from exposure that has occurred at work, rather than from non-occupational exposure. Workplace exposure to asbestos kills more people than any other single work-related illness. The diseases can take from 15 to 60 years to develop – so the person who has breathed in the fibres is not immediately aware of any change in their health. Asbestos can cause two main types of disease in humans: asbestosis (scarring of lung tissue) and cancer (particularly lung cancer and mesothelioma).

MMMFs can in some circumstances cause irritation of the skin and eyes and upper respiratory tract. You can find further detail of these effects in HSE Man-made mineral fibres OC 267/2.

Asbestos monitoring

There are no standard methods for monitoring fibres in ambient air around waste management facilities. Therefore, procedures have been adopted based on modifications of published methods for occupational monitoring.

Manual sampling of fibres is undertaken in much the same way as for many other particulates, using air-sampling pumps and filters. You can use several analytical end methods to identify and quantify the collected fibres. This is outlined in MDHS 87 (see MDHS 87 HSE Books 1999 ISBN 0 7176 1487 5).

MDHS 87 outlines the two main methods of quantifying the collected asbestos from air samples – optical microscopy, and electron microscopy.

Use the optical microscopy method given in HSE guidance HSG 248 as the routine approach for monitoring ambient air. Note that this method is principally for controlled conditions in premises and workplaces, and dusty outdoor conditions. The procedure uses a membrane filter method. Fibres collected on the filter are counted using phase contrast microscopy (PCM) to obtain the countable fibre number concentration in air.

PCM is the analytical method of choice for occupational monitoring of asbestos, because of the following advantages over other methods:

• the technique is specific for countable fibres as it excludes non-fibrous particles from the count
• the technique is relatively inexpensive
• you can perform the analysis quickly and on-site for rapid determination of air concentrations of asbestos fibres
• the technique has continuity with historical epidemiological studies so that you can make estimates of expected disease
• from long-term determinations of asbestos exposures

The main disadvantage of PCM is that it does not positively identify asbestos fibres. Other fibres that are not asbestos may be included in the count if deemed a countable fibre by HSG 248. A further disadvantage of PCM is that the smallest visible fibres are about 0.2 µm in diameter while the finest asbestos fibres may be as small as 0.02 µm in diameter. For some exposures, substantially more fibres may be present than are counted. Other fibres can also interfere with counting, including fibreglass, anhydrite, plant fibres, perlite veins, gypsum, some synthetic fibres, membrane structures, sponge spicules, diatoms, micro-organisms, and wollastonite. Positive identification of asbestos must be performed by dispersion staining or electron microscopy techniques. Fibre counting is not suited to very dusty atmospheres, and high levels of general environmental dust can render samples unreadable by PCM.

Electron microscopy can detect much smaller fibres than optical microscopy. Quantification is by counting of fibres, but positive confirmation of fibres as asbestos on selected areas of the filter can also be made. This makes the electron microscope method preferable when there are significant levels of non-asbestos fibres in the air.

In summary, for monitoring around waste facilities the preferred method will usually be sampling onto membrane filters, followed by fibre counting by PCM in accordance with HSG 248. If difficulties with interferences are experienced with PCM, then electron microscopy should be used as the end method. One practical approach that can be taken is to divide the exposed filter paper in half and immediately analyse the first half by PCM. Then, if necessary, the other half of the filter paper can later be analysed by electron microscopy to establish the PCM-equivalent asbestos fibres concentrations.

We provide further information on techniques and standards for monitoring asbestos in our index of methods.

Several direct-reading instruments operating on the light scattering principle are used as portable fibre counters in occupational hygiene work, but their suitability for ambient applications is unproven. The instruments rely on being able to first align fibres before they pass into the optical sensor. However, they cannot match the performance of manual methods and are best used only for an indication of whether levels are increasing or decreasing.

Man-made mineral fibres

The UK occupational method MDHS 59 offers two approaches for monitoring man-made mineral fibre concentrations:

• sampling by cellulose ester filter followed by gravimetric determination, or sampling onto a filter followed by plasma ashing
• fibre counting by polarised light microscopy

The gravimetric approach is not well suited to ambient air because the method is non-specific and other atmospheric dusts would interfere significantly.

The fibre counting method is preferred for monitoring around waste facilities, it is similar in principle to that for asbestos.

We provide further information on techniques and standards for monitoring in our index of methods.

Asbestos limits and guideline levels

Asbestos is a proven human carcinogen (IARC Group 1). No safe level can be proposed for asbestos because a safe threshold is not known to exist. Exposure should be prevented but where that is not possible, it should be minimised. Asbestos should not be found above background levels at site boundaries.

Occupational exposure limits exist for MMMF (refer to the latest issue of Guidance Note EH 4059 and to Operational Circular HSE OC 267/260). But for ambient air, no Environmental Assessment Leve (EAL) is currently listed in the H1 environmental risk assessment tool for permits . The are no plans to consider alternative thresholds for asbestos due to there being no safe level.

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Published 10 September 2024