@article{fdi:010069345,
  title = {{G}lobal scale variability of the mineral dust long-wave refractive index : a new dataset of in situ measurements for climate modeling and remote sensing},
  author = {{D}i {B}iagio, {C}. and {F}ormenti, {P}. and {B}alkanski, {Y}. and {C}aponi, {L}. and {C}azaunau, {M}. and {P}angui, {E}. and {J}ournet, {E}. and {N}owak, {S}. and {C}aquineau, {S}andrine and {A}ndreae, {M}. {O}. and {K}andler, {K}. and {S}aeed, {T}. and {P}iketh, {S}. and {S}eibert, {D}. and {W}illiams, {E}. and {D}oussin, {J}. {F}.},
  editor = {},
  language = {{ENG}},
  abstract = {{M}odeling the interaction of dust with long-wave ({LW}) radiation is still a challenge because of the scarcity of information on the complex refractive index of dust from different source regions. {I}n particular, little is known about the variability of the refractive index as a function of the dust mineralogical composition, which depends on the specific emission source, and its size distribution, which is modified during transport. {A}s a consequence, to date, climate models and remote sensing retrievals generally use a spatially invariant and time-constant value for the dust {LW} refractive index. {I}n this paper, the variability of the mineral dust {LW} refractive index as a function of its mineralogical composition and size distribution is explored by in situ measurements in a large smog chamber. {M}ineral dust aerosols were generated from 19 natural soils from 8 regions: northern {A}frica, the {S}ahel, eastern {A}frica and the {M}iddle {E}ast, eastern {A}sia, {N}orth and {S}outh {A}merica, southern {A}frica, and {A}ustralia. {S}oil samples were selected from a total of 137 available samples in order to represent the diversity of sources from arid and semi-arid areas worldwide and to account for the heterogeneity of the soil composition at the global scale. {A}erosol samples generated from soils were re-suspended in the chamber, where their {LW} extinction spectra (3-15 mu m), size distribution, and mineralogical composition were measured. {T}he generated aerosol exhibits a realistic size distribution and mineralogy, including both the sub-and super-micron fractions, and represents in typical atmospheric proportions the main {LW}-active minerals, such as clays, quartz, and calcite. {T}he complex refractive index of the aerosol is obtained by an optical inversion based upon the measured extinction spectrum and size distribution. {R}esults from the present study show that the imaginary {LW} refractive index (k) of dust varies greatly both in magnitude and spectral shape from sample to sample, reflecting the differences in particle composition. {I}n the 3-15 mu m spectral range, k is between similar to 0.001 and 0.92. {T}he strength of the dust absorption at similar to 7 and 11.4 mu m depends on the amount of calcite within the samples, while the absorption between 8 and 14 mu m is determined by the relative abundance of quartz and clays. {T}he imaginary part (k) is observed to vary both from region to region and for varying sources within the same region. {C}onversely, for the real part (n), which is in the range 0.84-1.94, values are observed to agree for all dust samples across most of the spectrum within the error bars. {T}his implies that while a constant n can be probably assumed for dust from different sources, a varying k should be used both at the global and the regional scale. {A} linear relationship between the magnitude of the imaginary refractive index at 7.0, 9.2, and 11.4 mu m and the mass concentration of calcite and quartz absorbing at these wavelengths was found. {W}e suggest that this may lead to predictive rules to estimate the {LW} refractive index of dust in specific bands based on an assumed or predicted mineralogical composition, or conversely, to estimate the dust composition from measurements of the {LW} extinction at specific wavebands. {B}ased on the results of the present study, we recommend that climate models and remote sensing instruments operating at infrared wavelengths, such as {IASI} (infrared atmospheric sounder interferometer), use regionally dependent refractive indices rather than generic values. {O}ur observations also suggest that the refractive index of dust in the {LW} does not change as a result of the loss of coarse particles by gravitational settling, so that constant values of n and k could be assumed close to sources and following transport. {T}he whole dataset of the dust complex refractive indices presented in this paper is made available to the scientific community in the {S}upplement.},
  keywords = {},
  booktitle = {},
  journal = {{A}tmospheric {C}hemistry and {P}hysics},
  volume = {17},
  numero = {3},
  pages = {1901--1929},
  ISSN = {1680-7316},
  year = {2017},
  DOI = {10.5194/acp-17-1901-2017},
  URL = {https://www.documentation.ird.fr/hor/fdi:010069345},
}