Determination of the refractive index of insoluble organic extracts from atmospheric aerosol over the visible wavelength range using optical tweezers
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Published:2018-04-18
Issue:8
Volume:18
Page:5235-5252
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ISSN:1680-7324
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Container-title:Atmospheric Chemistry and Physics
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language:en
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Short-container-title:Atmos. Chem. Phys.
Author:
Shepherd Rosalie H., King Martin D.ORCID, Marks Amelia A., Brough Neil, Ward Andrew D.
Abstract
Abstract. Optical trapping combined with Mie spectroscopy is a new technique used to
record the refractive index of insoluble organic material extracted from
atmospheric aerosol samples over a wide wavelength range. The refractive
index of the insoluble organic extracts was shown to follow a Cauchy equation
between 460 and 700 nm for organic aerosol extracts collected from urban
(London) and remote (Antarctica) locations. Cauchy coefficients for the
remote sample were for the Austral summer and gave the Cauchy coefficients of
A = 1.467 and B = 1000 nm2 with a real refractive index of
1.489 at a wavelength of 589 nm. Cauchy coefficients for the urban samples
varied with season, with extracts collected during summer having Cauchy
coefficients of A=1.465±0.005 and
B=4625±1200 nm2 with a representative real refractive index
of 1.478 at a wavelength of 589 nm, whilst samples extracted during autumn
had larger Cauchy coefficients of A = 1.505 and B = 600 nm2
with a representative real refractive index of 1.522 at a wavelength of
589 nm. The refractive index of absorbing aerosol was also recorded. The
absorption Ångström exponent was determined for woodsmoke and humic
acid aerosol extract. Typical values of the Cauchy coefficient for the woodsmoke
aerosol extract were A=1.541±0.03 and
B=14800±2900 nm2, resulting in a real refractive index of
1.584 ± 0.007 at a wavelength of 589 nm and an absorption
Ångström exponent of 8.0. The measured values of refractive index
compare well with previous monochromatic or very small wavelength range
measurements of refractive index. In general, the real component of the
refractive index increases from remote to urban to woodsmoke. A
one-dimensional radiative-transfer calculation of the top-of-the-atmosphere
albedo was applied to model an atmosphere containing a 3 km thick layer of
aerosol comprising pure water, pure insoluble organic aerosol, or an
aerosol consisting of an aqueous core with an insoluble organic shell. The
calculation demonstrated that the top-of-the-atmosphere albedo increases by
0.01 to 0.04 for pure organic particles relative to water particles of the
same size and that the top-of-the-atmosphere albedo increases by 0.03 for aqueous
core-shell particles as volume fraction of the shell material increases to
25 %.
Publisher
Copernicus GmbH
Subject
Atmospheric Science
Reference112 articles.
1. Adler, G., Flores, J. M., Abo Riziq, A., Borrmann, S., and Rudich, Y.:
Chemical, physical, and optical evolution of biomass burning aerosols: a case
study, Atmos. Chem. Phys., 11, 1491–1503, https://doi.org/10.5194/acp-11-1491-2011,
2011. 2. Ajtai, T., Filep, A., Utry, N., Schnaiter, M., Linke, C., Bozoki, Z., Szabo,
G., and Leisner, T.: Inter-comparison of optical absorption coefficients of
atmospheric aerosols determined by a multi-wavelength photoacoustic
spectrometer and an Aethalometer under sub-urban wintry conditions,
J. Aerosol Sci., 42, 859–866, https://doi.org/10.1016/j.jaerosci.2011.07.008, 2011. 3. Andreaea, M. O. and Rosenfeld, D.: Aerosol–cloud–precipitation
interactions. Part 1. The nature and sources of cloud-active aerosols,
Earth-Sci. Rev., 89, 13–41, https://doi.org/10.1016/j.earscirev.2008.03.001, 2008. 4. Arnold, A., Spock, D. E., and Folan, L. M.: Electric-field-modulated light
scattering near a morphological resonance of a trapped aerosol particle, Opt.
Lett., 15, 1111–1113, https://doi.org/10.1364/OL.15.001111, 1990. 5. Barkey, B., Paulson, S. E., and Chung, A.: Genetic Algorithm Inversion of
Dual Polarization Polar Nephelometer Data to Determine Aerosol Refractive
Index, Aerosol Sci. Tech., 41, 751–760, https://doi.org/10.1080/02786820701432640,
2007.
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