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Utilization of different sensor-type measurement techniques leads to more comprehensive results in urban particulate matter measurements

Utilization of different sensor-type measurement techniques leads to more comprehensive results in urban particulate matter measurements

Two different methods of measuring atmospheric particles were tested in Helsinki.

Atmospheric particle sizes vary from few nanometers to several tens of micrometers. As no universal measurement method exists for the whole particle size range, several different techniques have to be used in parallel in order to achieve necessary coverage.

Finnish Meteorological Institute conducted research in co-operation with Tampere University of Technology, Helsinki Region Environmental Services Authority (HSY) and Pegasor Oy, where three month long urban air quality measurements were carried out at the Supersite measurement station in Mäkelänkatu, Helsinki. The study investigated the applicability of optical and a diffusion charged-based sensors to urban air quality measurements.

"The optical aerosol sensor developed at the Finnish Meteorological Institute is quite simple and has relatively wide operational range when considering different particle sizes", says Joel Kuula from Finnish Meteorological Institute. "However, it cannot measure particles smaller than 500 nanometers with appropriate reliability and hence nanoparticles originating from combustion processes are out of its reach. This is a problem when considering urban air quality assessments and vehicular exhaust emission measurements, in particular."

Contrary to the optical aerosol sensor, the method developed by Pegasor equipment relies on electrical charging of particles. This method enables detectability of very small, combustion related particles. The weakness is the subpar particle charging efficiency at 400 nanometers and beyond, but in practice this is not a problem if the measurements have been aimed at vehicular exhaust emissions and residential wood burning, specifically.

Out of all anthropogenic particulate matter sources vehicular exhaust emissions are the ones containing smallest particles. Fresh exhaust gasses typically comprise of particles of 10 nanometers in size, but certain mechanisms and chemical reactions may end up growing the particle – or particle agglomerate in this case – multifold in size (e.g. 100 nanometers = 0.0001 millimeters). Roughly speaking, the same applies for residential wood burning emissions. Mean particle size of a street dust may, on the other hand, be several or even tens of micrometers and hence entail completely different physical characteristics.

In the future air quality monitoring has been envisioned to be conducted with dense sensor networks. Scientists suggest that the cost-effectiveness and usability of these networks are optimized when one or several different techniques are used together or separately, depending on which parameters are intended to be measured.

Further information:

researcher Joel Kuula, Finnish Meteorological Institute, tel. +358 447 227 718,

Kuula J., Kuuluvainen H., Rönkkö T., Niemi J. V., Saukko E., Portin H., Aurela M., Saarikoski S., Rostedt A., Hillamo R., Timonen H. 2019. Applicability of Optical and Diffusion Charging-Based Particulate Matter Sensors to Urban Air Quality Measurements. Aerosol and Air Quality Research, doi: 10.4209/aaqr.2018.04.0143

This study was funded by Business Finland funded INKA-ILMA/EAKR project, CITYZER  and by the Regional innovations and experimentations funds AIKO, governed by the Helsinki Uusimaa Regional Council.

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