The quality of the air we breathe is a critical factor for public health and the environment, but also a key element in the operational management and regulatory compliance of many activities.
One of the pollutants most closely monitored for their adverse effects is Particulate Matter PM, especially the respirable (PM10), fine (PM2.5) and ultrafine (UFP) particles, which have been the focus of attention in recent years thanks to the most recent research.
In this article we offer you a complete guide on how to measure and control particulate matter, the technologies and regulations to be applied and some practical cases in which the importance of these measurements becomes clear.
How are particulate air pollutants classified?
In addition to oxygen, nitrogen, CO2 or water vapor, the earth’s atmosphere contains other substances in its composition that can give rise to certain air pollutants.
The classification and negative effects of suspended particles vary according to their nature, origin or size, the latter being the most important characteristic.
The nature and chemical composition of air pollutant particles is highly variable and heterogeneous: they can be solid or liquid and are composed of a complex mixture of substances of both organic and inorganic origin.
The chemical composition of particulate matter is conditioned, to a large extent, by the emission sources and the transformations it undergoes during its atmospheric transport.
Basically and as Li, Jin & Kan in their research article state they are a “mixture of chemicals (hydrocarbons, salts and other compounds emitted by vehicles, kitchens and industry) and other natural components such as dust and microorganisms whose toxicity varies depending on place and time”.
If, on the other hand, we look at their origin, suspended particles can originate both from natural causes – such as Saharan dust or forest fires – and anthropogenic activities.
Primary sources release particulate matter directly into the atmosphere, including emissions from vehicles, industrial activities or agricultural processes, among others.
On the other hand, secondary sources indirectly form particles in the atmosphere through chemical reactions between gaseous precursor compounds such as sulfur dioxide (SO2), nitrogen oxides (NOx), ammonia (NH3) and volatile organic compounds (VOCs).
All this information is expanded in our article “Primary and secondary pollutants: these are the most dangerous”.
Airborne particles, commonly referred to as particulate matter (PM), are a heterogeneous group of microscopic elements floating in the air. These particles can be solid or liquid and are composed of a complex mixture of substances of both organic and inorganic origin.
The last – and most common – classification is to classify particles based on their aerodynamic size or diameter, a key aspect that will largely determine their dispersion in the atmosphere and the effects on the human respiratory system.
The size of the particles is a critical factor in their hazardousness: the smaller their diameter, the longer they remain suspended in the atmosphere and the greater the risk they represent.
The literature distinguishes several particle sizes:
- Coarse particles: are those with a diameter less than or equal to 10 microns – µm.
- Fine particles, whose size is less than or equal to 2.5 microns – µm.
- Ultra-fine particles, with a diameter of less than 0.1 microns – µm.
The following graph shows the size of coarse and fine particles in relation to the diameter of a human hair.
Source: United States Environmental Protection Agency
Classification of PM particles:
- By nature: very variable cataloguing linked to the chemical composition that depends on the emission sources and the transformations undergone by the particles during atmospheric transport.
- By their origin: they are classified as primary sources when they are emitted directly into the atmosphere and secondary sources when they originate from transformation in the atmosphere.
- By size: this is the most common classification as it is a key aspect in the effects on human health. They are divided into:
- Coarse particles or PM10: diameter less than or equal to 10 microns – µm.
- Fine particles or PM2.5: size less than or equal to 2.5 microns – µm.
- Ultra fine particles or UFP: diameter less than 0.1 microns – µm.
Why monitor and control particulate matter? Health and environmental impacts
The aim of monitoring and controlling PM particles in suspension encompasses multiple reasons, such as:
- Protecting public health
- Protecting the environment
- Controlling the impact on the economy
- Ensuring regulatory compliance.
As mentioned above, one of the most critical reasons is their effects on human health.
As early as 2012, Kelly & Fussell concluded in their research that large particles (up to 100 µm) are retained in the nasopharyngeal passages, while coarse particles up to 10 µm (PM10) are mainly deposited in the primary bronchi; on the other hand, particles smaller than about 2.5 µm (PM2.5) penetrate directly into the alveoli and terminal bronchioles.
In fact, both PM2.5 and ultrafine particles (UFP) can penetrate deep into the respiratory system and reach the bloodstream, aggravating respiratory, cardiovascular and neurological diseases, mainly in the most vulnerable groups such as children, the elderly, pregnant women and people with pre-existing conditions.
Added to this are the social and health costs associated with poor air quality, which in Europe amount to approximately 1,250€ per inhabitant per year, according to a study published in 2020.
The harmful effects of particles on human health and the environment, as well as the high social and healthcare costs associated with poor air quality, led the WHO to state the need for urgent action by revising its Air Quality Guidelines in 2021 and the European Union to draft Directive EU 2024/2881, the most recent version, which adopts stricter limit valuesto comply with the 2050 Zero Pollution Plan.
What does the legislation say about airborne particles?
The direct relationship between particle size and its biological impact and the growing scientific evidence on the effects of particulate pollution on health and the environment has prompted a major change in the legislative framework.
From now on, the legislation has the clear objective of minimizing the harmful effects through the measures established in the “Zero Pollution” Action Plan for 2050, as set out in the new EU Directive 2024/2881. Air Quality
Among these measures, stricter limit values are established for PM10 and PM2.5 and the monitoring of new emerging pollutants such as Ultra Fine Particles (UFP) and Black Carbon is incorporated in the so-called super control sites.
To date, in Spain the legal framework establishing the regulations for the monitoring and control of PM particles includes:
- Law 34/2007, of November 15, 2007, on air quality and atmospheric protection, which establishes the general framework for air quality.
- Royal Decree 102/2011, of January 28, on the improvement of air quality, defines air quality objectives for various pollutants, including particulate matter.
- Royal Decree 1052/2022 of December 27, 2002, which regulates low emission zones (ZBE) and seeks to improve air quality and mitigate the effects of road traffic in urban environments.
How are particles in the air measured? The most relevant monitoring technologies
In order to answer the question of how to measure particles in the air, it is important to first distinguish between emissions and immissions, as the instrumentation and measurement methods will vary depending on this.
As explained in our article ‘Main differences between emissions and immissions’, emissions are related to sources that emit pollutants into the atmosphere (such as industries and energy production plants, for example), while immissions refer to the concentration of a pollutant present in the atmosphere at a given moment or period.
Since the pollutants present in emissions undergo a series of transformations in the atmosphere, it is important to measure and control both emissions and immissions, also differentiating between outdoor and indoor air quality.
- Measurement of particulate matter in emission
- Monitoring of particulate matter in ambient air
- Indoor particle measurement
Measurement of particulate matter in emission
The monitoring of particulate emissions from industrial stationary sources is crucial to comply with environmental regulations, avoid administrative sanctions and protect the atmosphere.
Two main approaches are used to measure PM particles at emission sources:
- Manual gravimetric method by isokinetic sampling.
- Automatic Continuous Emissions Monitoring Systems (CEMS).
The isokinetic sampling train is a system of equipment for sampling particulate matter in emissions from stationary sources and one of the most important devices for the collection of representative emission samples.
This manual system is based on filtration as a sampling technique and on the pressure difference generated in a Pitot tube as a velocity meter, in addition to ensuring that the velocity of the incoming sample is the same as that of the gas flow in the stack.
The UNE-EN 15259 standard is in charge of specifying the requirements and the necessary checks for sampling, guaranteeing its reliability and reproducibility.
The disadvantage of this system is that it is a manual process – not in real time – which requires specialized personnel and rigorous calibration.
Source: NMX-AA-010-SCFI-2001
On the other hand, CEMS or Continuous Emissions Monitoring Systems are integrated systems that are designed to continuously measure the concentration of particulate matter from stationary sources in order to demonstrate regulatory compliance.
As detailed in the article “CEMS emission monitoring systems: what they are, types and characteristics“, we can differentiate between Extractive CEMS, which capture the sample, condition it and transport it to an analyzer, or in-situ CEMS, in which the monitor is installed directly in the chimney, minimizing pollutant losses.
The specific operating principles for particle measurement in CEMS are varied:
- Opacimeters: measure the decrease in light transmission through the stack due to the presence of particulate matter.
- Electrodynamic: particle measurement is based on the interaction between electric current and magnetic field to determine the concentration or mass of particles in a medium.
Among the applicable standards in this area are EN 14181 “Emissions from stationary sources – Quality assurance of automatic measurement systems” which specifies procedures for establishing three quality assurance levels (QALs) and an Annual Surveillance Test (AST), EN15267-3, which establishes the performance requirements for type approval and EN 13284-2, related to the determination of particulate matter in emissions at low concentrations by automatic methods.
EPA Title 40 CFR also establishes reference methods for measuring particulate matter in emissions.
The evolution of CEMS towards integration and quality assurance has turned them into integrated systems that include data acquisition and software for validation and reporting, providing comprehensive, verifiable and auditable monitoring.
The evolution of CEMS towards integration and quality assurance has turned them into integrated systems that include data acquisition and software for validation and reporting, providing comprehensive, verifiable and auditable monitoring.
Monitoring of particulate matter in ambient air
Monitoring ambient air quality is essential for assessing population exposure, judging compliance with standards and observing pollution trends. Various methods and instruments are used for this purpose, such as:
Reference gravimetric method
This is the reference standard for determining the mass concentration of PM10 and PM2.5. The particle concentration is determined manually by recording the weight of the filter before and after sampling and the volume of air sampled. The key instruments for this method are:
-
- High-volume samplers
- Low-volume samplers
To ensure the reliability of the measurements, the samplers must have a certificate of conformity in accordance with the UNE-EN 12341:2023 standard. Despite its accuracy, the gravimetric method requires a rigorous manual process that prevents real-time results from being obtained.
Equivalent automatic methods
These methods determine the concentration of particulate matter in real time, taking advantage of the physical properties of the particles. Some of the main instruments are:
- Beta Attenuation Monitors (BAM): particles are collected on a paper filter and exposed to beta rays. The attenuation of the beta rays is directly proportional to the mass of particles on the filter. An example of this monitor is the BAM 1020 device from Met One Instruments.
- Optical light scattering methods: a light source (often a laser) illuminates the particles and a light sensor detects the intensity of the scattered light. The intensity of the scattered light is proportional to the mass concentration of the particles. The Palas Fidas 200 device is an example of this type of instrumentation.
The UNE-EN 16450:2017 standard is crucial in this context and specifies which technologies can be considered equivalent to the reference method in terms of the reliability, homogeneity and comparability of the data provided.
The different instruments for measuring suspended particles are located, together with the rest of the analysers for pollutant gases and meteorological parameters, in the fixed stations that make up the Air Quality Networks.
They can also be configured within a mobile station to carry out specific measurement campaigns or respond to episodes of exceedances with accurate, reliable and valid data for the authorities.
Sensors for measuring suspended particles
Particle monitoring sensors using IoT technology are suitable for a wide range of low-cost applications. They require minimal maintenance and provide historical and real-time data with values very close to those of standardised methods.
One example is the Nanoenvi EQPM particle monitor, whose core technology is the light scattering-based optical particle counter (OPC), which allows it to measure multiple PM fractions with a very strong correlation to reference and equivalent methods.
Their small size and low cost allow for general information and control over air quality (dust control on construction sites, perimeter monitoring, complementary measurements and preliminary studies in LEZs, etc.), but it is important to note that their data are not valid in a regulatory context (sending data to government agencies).
The main benefit of low-cost particle monitoring sensors is that they provide accurate, real-time data on PM particle concentrations at a low cost. Their small size and low maintenance make them the preferred option for informative air quality monitoring in numerous applications.
Particle measurement in indoor environments
As we have seen, there is growing concern about measuring and controlling pollutants such as PM particles in ambient air. People spend approximately 90% of their time indoors, so it is logical and equally important to measure indoor air quality.
Although indoor PM levels are similar to or lower than outdoor levels, activities such as cooking, smoking or cleaning can be sources of dust and airborne particles.
This can aggravate existing cardiovascular and respiratory conditions in occupants, such as allergies and asthma, and is particularly critical in hospital environments due to the direct influence of airborne dust on the spread of nosocomial diseases.
There are several monitoring systems available on the market, which can be divided into:
- Portable monitors, which allow PM levels to be checked in real time at different points in a building, a feature that is particularly useful for evaluating a building’s filtration systems.
- Fixed meters, which are generally multi-parameter devices that allow IAQ to be measured and monitored continuously.
Among these devices, Nanoenvi IAQ stands out as a multiparametric indoor air quality meter that integrates different IoT sensors and can be used both portably and fixed, providing continuous, real-time data on the main IAQ parameters.
The benefits of using this type of monitor to measure indoor air quality will allow us to avoid health problems, productivity losses in the workplace and facilitate the implementation of appropriate ventilation strategies.
Where is important to monitor airborne PM Particles? Graphic example
Conclusion: how to measure airborne particles complete guide
Recent scientific evidence on the effects of particulate matter on human health and the environment has led to growing interest in measuring and controlling airborne particles.
The question is then, how are PM particles measured in the air? Depending on the context—emission, immission or indoor air quality—and the applicable regulations, we will have:
- Measuring PM particles in emissions. This can be done by:
- Manual gravimetric method by isokinetic sampling
- Continuous Emission Monitoring Systems (CEMS).
- Monitoring particulate matter in ambient air. There are several options, such as:
- Fixed or mobile measuring stations that include:
- Manual gravimetric methods of reference such as high or low volume collectors.
- Automatic methods with proven equivalence such as Beta Attenuation Monitors (BAM) or optical light scattering methods.
- Low-cost sensors for obtaining general information on air quality in multiple applications and uses (data not valid for government agencies).
- Fixed or mobile measuring stations that include:
- Measurement of particles in indoor environments.
- Portable meters, useful for evaluating the effectiveness of filtration systems.
- Fixed monitors, which allow uninterrupted monitoring of the air quality in a space.
Sources:
– Kelly, F. J., & Fussell, J. C. (2012). Size, source and chemical composition as determinants of toxicity attributable to ambient particulate matter. Atmospheric Environment, Vol. 60, pp. 504–526. doi:http://doi.org/f4c88t
– Khan, B. (2016). Inorganic and organic pollutants in atmospheric aerosols: chemical composition and source apportionment. Università Ca’Foscari Venezia. http://dspace.unive.it/bitstream/handle/10579/8350/956030-1175891.pdf
– Lequy, E., Siemiatycki, J., Leblond, S., Meyer, C., Zhivin, S., & Vienneau, D. et al. (2019). Long-term exposure to atmospheric metals assessed by mosses and mortality in France. Environment International, 129, 145-153. doi: http://doi.org/c6tk
– Li, X., Jin, L., & Kan, H. (2019). Air pollution: a global problem needs local fixes. Nature, 570(7762), 437-439. doi: http://doi.org/c85v
– McFiggans, G., Alfarra, M. R., Allan, J. D., Coe, H., Hamilton, J. F., Harrison, R. M., Jenkin, M. E., Lewis, A. C., Moller, S.J., Topping, D. O., and Williams, P. I. (2015). A review of the state-of-the science relating to secondary particulate matter of relevance to the composition of the UK atmosphere. Full technical report to Defra, project AQ0732
– Salvador, P., & Artiñano, B. (2000). Evaluación de la contaminación atmosférica producida por partículas en suspensión en las redes de calidad del aire de la Comunidad de Madrid. Madrid: CIEMAT. ISSN 1135-9420
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