16 May 2022
16 May 2022
Status: this preprint is currently under review for the journal AMT.

Performance analysis of the NanoScan SMPS and the Mini WRAS Ultrafine Aerosol Particle Size Spectrometers

Ajit Ahlawat1, Kay Weinhold1, Jesus Marval2, Paolo Tronville2, Ari Leskinen3,4, Mika Komppula3, Holger Gerwig5, Lars Gerling6, Stephan Weber6, Rikke Bramming Jørgensen7, Thomas Nørregaard Jensen8, Marouane Merizak9, Ulrich Vogt9, Carla Ribalta10, Mar Viana11, Andre Schmitz12, Maria Chiesa13, Giacomo Gerosa13, Lothar Keck14, Markus Pesch14, Gerhard Steiner14, Thomas Krinke15, Torsten Tritscher15, Wolfram Birmili16, and Alfred Wiedensohler1 Ajit Ahlawat et al.
  • 1Leibniz Institute for Tropospheric Research, Permoserstrasse 15, 04318 Leipzig, Germany
  • 2Politecnico di Torino - DENERG, Corso Duca degli Abruzzi 24, 10129 Turin, Italy
  • 3Finnish Meteorological Institute, Yliopistonranta 1 F, 70210 Kuopio, Finland
  • 4University of Eastern Finland, Yliopistonranta 1 F, 70210 Kuopio, Finland
  • 5Umweltbundesamt, Paul-Ehrlich-Straße 29, 63225 Langen, Germany
  • 6Technische Universität Braunschweig, Institute of Geoecology, Langer Kamp 19c, 38106 Braunschweig, Germany
  • 7Norwegian University of Science and Technology, Department of Industrial Economics and Technology Management, 7491 Trondheim, Norway
  • 8Center for Air and Sensor Technology, Danish Technological Institute, DK-8000 Aarhus C, Denmark
  • 9Institut für Feuerungs- und Kraftwerkstechnik (IFK), Universität Stuttgart, Pfaffenwaldring 23 70569 Stuttgart, Germany
  • 10Det Nationale Forskningscenter for Arbejdsmiljø, Lersø Parkallé 105, 2100 København Ø, Denmark
  • 11Institute of Environmental Assessment and Water Research (IDAEA-CSIC), Jordi Girona 18, 08034 Barcelona, Spain
  • 12Wessling GmbH, Oststraße 7, 48341 Altenberge, Germany
  • 13Università Cattolica del Sacro Cuore, Department of Mathematics and Physics, Via della Garzetta 48, 25133 Brescia, Italy
  • 14GRIMM Aerosol Technik Ainring GmbH & Co. KG, Dorfstrasse 9, 83404 Ainring, Germany
  • 15TSI GmbH, Neuköllner Str. 4, 52068 Aachen, Germany
  • 16Umweltbundesamt, Corrensplatz 1, 14195 Berlin, Germany

Abstract. In aerosol science, there is an increasing interest to perform mobile measurements to obtain number size distribution of ultrafine particles (UFP), using portable instruments based on unipolar charging and size segregation by electrical particle mobility. Applications of such measurements range from ambient and indoor aerosol studies to source identification in work environments. However, knowledge on the actual measurement uncertainties of these portable instruments under various conditions has been limited. This investigation presents results from an intercomparison workshop conducted at the World Calibration Center for Aerosol Physics (WCCAP) in Leipzig, Germany, in January 2020. Manufacturers and users were invited to have their portable instruments tested and compared against reference instrumentation for particle number size distributions (PNSD) and total particle number concentration (PNC). In particular, the performances and uncertainties of the NanoScan SMPS (Scanning Mobility Particle Sizer) Model 3910 (TSI Inc.) and the Mini Wide Range Aerosol Spectrometer (WRAS) Model 1371 (Grimm Aerosol Technik) were investigated extensively against the WCCAP Mobility Particle Size Spectrometers (MPSS) and Condensation Particle Counters (CPC). A total of 11 TSI NanoScan SMPS and 4 GRIMM Mini WRAS instruments were characterized for ambient aerosols as well as lab-generated aerosols.

The workshop results affirm that the portable instruments must be serviced and calibrated annually or prior field studies to provide measurements within the given uncertainties. It should be noted that users should carry out timely service, maintenance and calibration of portable instruments at their facilities. During initial inspection, non-serviced NanoScan SMPS instruments overestimated a dominant ultrafine aerosol mode by 120 % at around 80 nm. Maintenance and servicing improved the performance. Overall, the performance of NanoScan SMPS instruments improved for the ultrafine aerosol mode while the PNC in the fine aerosol mode still overestimated by up to 80 %. The latter effect seems to be systematically related to the unipolar charging of particles, and the reduced sensitivity of electrical particle mobility with increasing particle size above 200 nm. Due to shift in the second mode of bimodal distribution, particles are overcounted around 100 nm. With regard to the integral PNC, some of the NanoScan SMPS found to be in good agreement (i.e. within 20 %) compared to the reference CPC. In addition, a reasonably good unit-to-unit agreement within ±20 % was found for NanoScan SMPS instruments. The Mini WRAS instruments, after proper cleaning and servicing, provided improved results within ±15 % deviation in PNC in the ultrafine aerosol mode. Overall, most of the GRIMM Mini WRAS instruments (operating with software version 10.0) agrees well with PNC (i.e. 10–50 %) when the ultrafine mode was dominant. Conversely, PNC of the fine aerosol mode was systematically underestimated by 60 % above 100 nm. Except for one instrument, the integral PNC of the GRIMM Mini WRAS spectrometers were within an uncertainty range of ±20 % compared to the reference CPC. Additionally, it is important for users to note that the Mini WRAS performed significantly better when using software version 10.0 compared to version 8.2.

The workshop results suggest that despite the above-mentioned uncertainties, these portable instruments are suited for mobile ultrafine particle measurements to detect relative differences in the PNSD such as source apportionment studies of ultrafine particles at work places or outdoors near sources.

Ajit Ahlawat et al.

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Short summary
Measurements of ultrafine particles must be done with quality-assured instruments. The performance of portable instruments such as NanoScan SMPS, and GRIMM Mini WRAS spectrometer measuring the particle number size distribution in the range from 10 to 200 nm were investigated. The influence of different aerosol types and maintenance activities on these instruments were explored. The results show that these portable instruments are suitable for mobile UFP measurements for source identification.