Aethalometer multiple scattering correction <i>C</i><sub>ref</sub> for mineral dust aerosols
In this study we provide a first estimate of the Aethalometer multiple scattering correction <i>C</i><sub>ref</sub> for mineral dust aerosols. <i>C</i><sub>ref</sub> is an empirical constant used to correct the aerosol absorption coefficient measure...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-08-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://www.atmos-meas-tech.net/10/2923/2017/amt-10-2923-2017.pdf |
| Summary: | In this study we provide a first estimate of the Aethalometer multiple
scattering correction <i>C</i><sub>ref</sub> for mineral dust aerosols.
<i>C</i><sub>ref</sub> is an empirical constant used to correct the aerosol
absorption coefficient measurements for the multiple scattering artefact of
the Aethalometer; i.e. the filter fibres on which aerosols are deposited
scatter light and this is miscounted as absorption. The <i>C</i><sub>ref</sub> at 450 and 660 nm was obtained from the
direct comparison of Aethalometer data (Magee Sci. AE31) with (i) the absorption
coefficient calculated as the difference between the extinction and
scattering coefficients measured by a Cavity Attenuated Phase Shift
Extinction analyser (CAPS PMex) and a nephelometer respectively at 450 nm
and (ii) the absorption coefficient from a MAAP (Multi-Angle Absorption
Photometer) at 660 nm. Measurements were performed on seven dust aerosol samples
generated in the laboratory by the mechanical shaking of natural parent soils
issued from different source regions worldwide. The single scattering albedo
(SSA) at 450 and 660 nm and the size distribution of the aerosols were also
measured.
<br><br>
<i>C</i><sub>ref</sub> for mineral dust varies between 1.81 and 2.56 for a SSA of
0.85–0.96 at 450 nm and between 1.75 and 2.28 for a SSA of 0.98–0.99 at
660 nm. The calculated mean for dust is 2.09 (±0.22) at 450 nm and 1.92 (±0.17)
at 660 nm. With this new <i>C</i><sub>ref</sub> the dust absorption coefficient by
the Aethalometer is about 2 % (450 nm) and 11 % (660 nm) higher
than that obtained by using <i>C</i><sub>ref</sub> = 2.14 at both 450 and
660 nm, as usually assumed in the literature. This difference induces a
change of up to 3 % in the dust SSA at 660 nm. The <i>C</i><sub>ref</sub>
seems to be independent of the fine and coarse particle size fractions, and
so the obtained <i>C</i><sub>ref</sub> can be applied to dust both close to sources
and following transport. Additional experiments performed with pure kaolinite
minerals and polluted ambient aerosols indicate <i>C</i><sub>ref</sub> of 2.49
(±0.02) and 2.32 (±0.01) at 450 and 660 nm (SSA = 0.96–0.97)
for kaolinite, and <i>C</i><sub>ref</sub> of 2.32 (±0.36) at 450 nm and 2.32
(±0.35) at 660 nm for pollution aerosols (SSA = 0.62–0.87 at
450 nm and 0.42–0.76 at 660 nm). |
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| ISSN: | 1867-1381 1867-8548 |