Intercomparison of 15 aerodynamic particle size spectrometers (APS 3321): uncertainties in particle sizing and number size distribution

Abstract

Abstract. Aerodynamic particle size spectrometers are a well-established method to measure number size distributions of coarse mode particles in the atmosphere. Quality assurance is essential for atmospheric observational aerosol networks to obtain comparable results with known uncertainties. In a laboratory study within the framework of ACTRIS (Aerosols, Clouds, and Trace gases Research Infrastructure Network), 15 aerodynamic particle size spectrometers (APS model 3321, TSI Inc., St. Paul, MN, USA) were compared with a focus on flow rates, particle sizing, and the unit-tounit variability of the particle number size distribution.Flow rate deviations were relatively small (within a few percent), while the sizing accuracy was found to be within 10 % compared to polystyrene latex (PSL) reference particles. The unit-to-unit variability in terms of the particle number size distribution during this study was within 10 % to 20 % for particles in the range of 0.9 up to 3 µm, which is acceptable for atmospheric measurements. For particles smaller than that, the variability increased up to 60 %, probably caused by differences in the counting efficiencies of individual units. Number size distribution data for particles smaller than 0.9 µm in aerodynamic diameter should only be used with caution. For particles larger than 3 µm, the unit-tounit variability increased as well. A possible reason is an insufficient sizing accuracy in combination with a steeply sloping particle number size distribution and the increasing uncertainty due to decreasing counting. Particularly this uncertainty of the particle number size distribution must be considered if higher moments of the size distribution such as the particle volume or mass are calculated, which require the conversion of the aerodynamic diameter measured to a volume equivalent diameter.In order to perform a quantitative quality assurance, a traceable reference method for the particle number concentration in the size range 0.5-3 µm is needed.

Comparison of methods for converting Dylos particle number concentrations to PM2.5 mass concentrations

“…Furthermore, the accuracy of the counting of particles was generally similar with small differences in the lower size range, where the APS seemed to be less accurate, and underestimating particles <0.7 µm. Pfeifer et al (2016) found for the APS that the variability in counting efficiency for particles <0.9 µm is 60% between different tested machines, which underline the findings of Peters et al (2006) . The OPC was less accurate in counting particles >2.5 µm, however, for this study this size range is not investigated .…”

“…In the present study, we developed two fit curves to convert Dylos for particles <0.9 µm is 60% between different tested machines, which underline the findings of Peters et al (2006). 25 The OPC was less accurate in counting particles >2.5 µm, however, for this study this size range is not investigated. 29 In two additional studies, it was shown that both the APS and the OPC mass concentrations were well in line with gravimetric samples, indicating that these devices are fairly capable of measuring PMC, 30,31 and are usable as a device to evaluate the performance of other real-time instruments.…”

Multi-Year ACSM measurements at the Central European Research Station Melpitz (Germany) Part I: Instrument Robustness, Quality Assurance, and Impact of Upper Size Cut-Off Diameter

“…The PNSD uncertainty determined 30 with the MPSS is approximately 10 %. The uncertainty of an APSS is between 10-30 %, depending on the size range (Pfeifer et al, 2016). The uncertainty of the MAAP is also within 10 % as determined by Müller et al (2011).…”

Characterization of aerosol properties at Cyprus, focusing on cloud condensation nuclei and ice nucleating particles

“…For the multiple charge correction (Wiedensohler, 1988) of the MPSS data, the APS data was accounted for in the inversion of the measured PNSD (Pfeifer et al, 2016). The combined PNSD is then given on the base of the volume equivalent particle diameter.…”