Particulate matter emissions and particulate matter measurementIn order to reduce emissions from certain sources, the particulate matter values must be recorded in a close-meshed network.

Particulate matter emissions

Metropolises like Stuttgart, Germany, or Highveld, South Africa, became infamous for their bad air quality and smog. Daily use of face masks against smog and the continuous absence of a blue sky in some regions peaked in the formulation of the new term ‘air-pocalypse’ in 2013 that stresses the enormous health issues from these conditions. Although for example Beijing managed to strongly reduce its average annual particulate matter up to 2.5 microns diameter (PM2.5) pollution levels between 2013 and 2022 by about two thirds, still the World Health Organization limits are even lower.
While pollutants like nitrous oxides from Diesel engines may be widely reduced during the electric revolution of personal transports, particulate matter is still generated by tires and brakes as well as other anthropogenic and natural sources like agriculture, industry or forest fires.

After only 15 years, the World Health Organization even lowered the PM limits in its air quality guidelines from 10 to 5 µg/m³ for PM2.5 and from 20 to 15 µg/m³ for particles up to 10 microns in diameter (PM10) in 2021. Air pollution is now considered as dangerous to health as smoking or unhealthy alimentation. Consequently, also the EU plans to lower the PM limits drastically in 2030.

The particle sources need to be identified and analyzed and PM distribution mechanisms have to be understood.

General measures like speed limits or laws against combustion engines and oil heating systems to meet the PM limits can be accompanied or avoided by the reduction of pollution from specific sources or for example dynamic traffic management. To reduce emissions from specific sources, PM levels have to be collected on a fine grid, the particle sources need to be identified and analyzed and PM distribution mechanisms have to be understood. Dynamic traffic management based on PM levels even needs real-time measurements.

Public agencies investigate PM values using scientific instruments which come with considerable investments and installation thresholds. Such measurements are suitable for point-wise investigation of PM in a coarse measurement network. Already a few streets away from the measurement location strong deviations are possible – depending on topography, buildings, wind or PM sources. For locations that were not selected by public agencies, the closest measurement values may already be invalid and even many kilometers away.

As a solution to this, much cheaper but still sufficiently accurate PM sensors are needed that can be installed easily and everywhere. Such devices can be used to provide a finer measurement grid for local information about the air pollution – leading to widespread knowledge of the local immission file:///A:/Marketing/Ago/14%20Stories-PR-Presse-Kombis/Feinstaub/Meteorological%20Technology%20International%20_%202023.docx#_msocom_1 and enabling distribution studies as well as source identification. At the same time, the measurements have to be reliable even if the scientific precision is not reached to the core.

Methods for measuring particulate matter
Classically, particulate matter is measured by deposition of particles on a filter. The filter is usually exchanged on a daily basis, dried and weighed in a laboratory. The relevant measurement values are consequently recorded as micrograms of dust on the filter per cubic meter of filtered air. Information about the chemical substances involved is not obtained regardless of the potentially different impact on the human body. The PM classes are derived from separation of the dust sizes by inertia-based impactor filters. The dust particles with diameters up to 2.5 microns in PM class 2.5 are also included in the fraction PM10.

Particulate matter sensors based on light scattering

As a different approach to obtain the particulate matter amount in the air, the measurement principle of light scattering is employed. Instead of repeated exchanges and weighing of filters in a laboratory, light scattered at particles in an air flow provides continuous information about the PM concentration. A photodetector is placed perpendicular to the air flow and also perpendicular to a light beam such that normally no light reaches the detector. When a particle crosses the beam the light is scattered and a part of it will reach the photo detector. The intensity of the received pulse conveys information about the cross section of the particle. Together with the air flow volume, the number density and size distribution of the particles can be obtained. In contrast to weighing dust on a filter, with this method the results can be transmitted in real time.
Working principle of a light scattering PM sensor. Scattered light from dust particles in an air stream is detected and evaluated to compute particulate matter densities

Important to notice is that this measurement principle conveys information about the reflectivity and cross section of the dust particle rather than its chemical composition or mass. Consequently, empirical algorithms process the information including the size distribution to convert the scattered light pulses into particle number densities and mass densities. The main advantages compared to the weighing method are a low installation threshold, low costs and the continuity of the measurements.

Particulate-Hygro-Thermo-Baro Sensor Compact measures temperature, humidity, PM2.5, PM10 and many other parameters with minimal installation effort.
Further product details

Particulate Hygro Thermo Baro Sensor Compact

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Our custom-fit mounting solutions enable attachment at all locations.

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Glossary of particulate matter measurement technology: Find out more about particulate matter measurement technology in our glossary‎‎

The Fine Dust Hygro-Thermo-Baro Sensor Compact (Fine Dust HTB Compact) measures the fine dust fractions PM1, PM2.5, PM4, PM10!

Thies CLIMA has developed a PM sensor for this application based on its meteorological Hygro-Thermo-Baro Transmitter Compact with a weather and radiation shield. The Particulate-Hygro-Thermo-Baro Sensor Compact measures the particulate matter fractions PM2.5 and PM10 together with precise meteorological basis information about temperature (± 0.1 °C), humidity (± 1.5 % r.h.) and air pressure (typ. ± 0.25 hPa). Accurate temperature readings and fast reaction times are provided by active and supervised ventilation of the hygro and thermo sensors.‎

For even more detailed investigations, also number densities and mass densities for the fractions up to 1 and 4 microns are measured and the number density for particles with diameters up to 0.5 microns is available. A measurement quality indicator is provided based on a combination of the PM values and the meteorological measured values. The sensor offers a RS485 interface with binary MODBUS-RTU and an ASCII protocol. With its ID-based communication operation in a bus system is possible.

Long-term exposure tests at the North Sea coastlineBuilt from corrosion-free materials, the Particulate-Hygro-Thermo-Baro Sensor Compact withstands long-term exposure tests at the North Sea coastline. Further long-term investigations directly at a public agency measurement container confirm the agreement between filter-based measurements and the Particulate-Hygro-Thermo-Baro Sensor Compact. The sensor is readily available and meets the requirements for distributed live monitoring of particulate matter levels.

Compared to the investments for public agency measurement containers, dozens of such sensors can be installed in a fine-grained network. Additionally, the sensors are operated continuously without frequent maintenance. Self-cleaning procedures and a robust design reduce personnel expenses
The Fine Dust Hygro-Thermo-Baro Sensor Compact (Fine Dust HTB Compact) measures the fine dust fractions PM1, PM2.5, PM4, PM10!

Very high level of agreement with the official gravimetric reference

PM2.5 measurement results of two Thies CLIMA particulate matter measuring devices (Particulate-hygro-thermo-baro sensor compact) and a close-by gravimetric measurement of a public agency.

Report: AIR-Pokalypse (Meteorological Technology World, 2023, September)

Sources of materials:
From ʻair-pocalypseʻ to blue skies. Beijingʻs fight for cleaner air is a rare victory for public dissent | CNN, , abgerufen am 21.06.2023
China: annual PM2.5 levels Beijing 2022 | Statista, /, abgerufen am 21.06.2023
WHO global air quality guidelines: particulate matter (‎PM2.5 and PM10)‎, ozone, nitrogen dioxide, sulfur dioxide and carbon monoxide, ISBN 9789240034228
Revision EU ambient air quality legislation (,

Further useful sources, links:
Glossary of particulate matter measurement technology: Find out more about particulate matter measurement technology in our glossary


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