Intercomparison of 15 aerodynamic particle size spectrometers (APS 3321): uncertainties in particle sizing and number size distribution
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...
| Main Authors: | , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-04-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | http://www.atmos-meas-tech.net/9/1545/2016/amt-9-1545-2016.pdf |
| Summary: | 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-to-unit variability of
the particle number size distribution.
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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-to-unit 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.
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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. |
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| ISSN: | 1867-1381 1867-8548 |