In:
Atmospheric Measurement Techniques, Copernicus GmbH, Vol. 14, No. 6 ( 2021-06-18), p. 4517-4542
Abstract:
Abstract. We evaluate the sensitivity of the size calibrations of
two commercially available, high-resolution optical particle sizers to
changes in aerosol composition and complex refractive index (RI). The
Droplet Measurement Technologies Ultra-High Sensitivity Aerosol Spectrometer (UHSAS) and the TSI, Inc. Laser Aerosol Spectrometer (LAS) are
two commonly used instruments for measuring the portion of the aerosol size
distribution with diameters larger than nominally 60–90 nm. Both instruments
illuminate particles with a laser and relate the single-particle light
scattering intensity and count rate measured over a wide range of angles to
the size-dependent particle concentration. While the optical block geometry
and flow system are similar for each instrument, a significant difference
between the two models is the laser wavelength (1054 nm for the UHSAS and
633 nm for the LAS) and intensity (about 100 times higher for the UHSAS), which
may affect the way each instrument sizes non-spherical or absorbing
aerosols. Here, we challenge the UHSAS and LAS with laboratory-generated,
mobility-size-classified aerosols of known chemical composition to quantify
changes in the optical size response relative to that of ammonium sulfate
(RI of 1.52+0i at 532 nm) and NIST-traceable polystyrene latex spheres
(PSLs with RI of 1.59+0i at 589 nm). Aerosol inorganic salt species are
chosen to cover the real refractive index range of 1.32 to 1.78, while
chosen light-absorbing carbonaceous aerosols include fullerene soot,
nigrosine dye, humic acid, and fulvic acid standards. The instrument
response is generally in good agreement with the electrical mobility
diameter. However, large undersizing deviations are observed for the
low-refractive-index fluoride salts and the strongly absorbing nigrosine dye and fullerene soot particles. Polydisperse size distributions for both fresh
and aged wildfire smoke aerosols from the recent Fire Influence on Regional
to Global Environments Experiment and Air Quality (FIREX-AQ) and the Cloud,
Aerosol, and Monsoon Processes Philippines Experiment (CAMP2Ex)
airborne campaigns show good agreement between both optical sizers and
contemporaneous electrical mobility sizing and particle time-of-flight mass
spectrometric measurements. We assess the instrument uncertainties by
interpolating the laboratory response curves using previously reported RIs
and size distributions for multiple aerosol type classifications. These
results suggest that, while the optical sizers may underperform for strongly
absorbing laboratory compounds and fresh tailpipe emissions measurements,
sampling aerosols within the atmospherically relevant range of refractive
indices are likely to be sized to better than ±10 %–20 % uncertainty over the submicron aerosol size range when using instruments calibrated with
ammonium sulfate.
Type of Medium:
Online Resource
ISSN:
1867-8548
DOI:
10.5194/amt-14-4517-2021
DOI:
10.5194/amt-14-4517-2021-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2021
detail.hit.zdb_id:
2505596-3
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