Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Journal topic

Journal metrics

Journal metrics

  • IF value: 5.509 IF 5.509
  • IF 5-year value: 5.689 IF 5-year 5.689
  • CiteScore value: 5.44 CiteScore 5.44
  • SNIP value: 1.519 SNIP 1.519
  • SJR value: 3.032 SJR 3.032
  • IPP value: 5.37 IPP 5.37
  • h5-index value: 86 h5-index 86
  • Scimago H index value: 161 Scimago H index 161
Volume 16, issue 3 | Copyright
Atmos. Chem. Phys., 16, 1565-1585, 2016
https://doi.org/10.5194/acp-16-1565-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 11 Feb 2016

Research article | 11 Feb 2016

Remote sensing of soot carbon – Part 1: Distinguishing different absorbing aerosol species

G. L. Schuster1, O. Dubovik2, and A. Arola3 G. L. Schuster et al.
  • 1NASA Langley Research Center, Hampton, VA, USA
  • 2Laboratoire d'Optique Atmosphérique, Université de Lille-1, CNRS, Villeneuve d'Ascq, France
  • 3Finnish Meteorological Institute, Kuopio, Finland

Abstract. We describe a method of using the Aerosol Robotic Network (AERONET) size distributions and complex refractive indices to retrieve the relative proportion of carbonaceous aerosols and free iron minerals (hematite and goethite). We assume that soot carbon has a spectrally flat refractive index and enhanced imaginary indices at the 440nm wavelength are caused by brown carbon or hematite. Carbonaceous aerosols can be separated from dust in imaginary refractive index space because 95% of biomass burning aerosols have imaginary indices greater than 0.0042 at the 675–1020nm wavelengths, and 95% of dust has imaginary refractive indices of less than 0.0042 at those wavelengths. However, mixtures of these two types of particles can not be unambiguously partitioned on the basis of optical properties alone, so we also separate these particles by size. Regional and seasonal results are consistent with expectations. Monthly climatologies of fine mode soot carbon are less than 1.0% by volume for West Africa and the Middle East, but the southern African and South American biomass burning sites have peak values of 3.0 and 1.7%. Monthly averaged fine mode brown carbon volume fractions have a peak value of 5.8% for West Africa, 2.1% for the Middle East, 3.7% for southern Africa, and 5.7% for South America. Monthly climatologies of free iron volume fractions show little seasonal variability, and range from about 1.1 to 1.7% for coarse mode aerosols in all four study regions. Finally, our sensitivity study indicates that the soot carbon retrieval is not sensitive to the component refractive indices or densities assumed for carbonaceous and free iron aerosols, and the retrieval differs by only 15.4% when these parameters are altered from our chosen baseline values. The total uncertainty of retrieving soot carbon mass is  ∼ 50% (when uncertainty in the AERONET product and mixing state is included in the analysis).

Download & links
Publications Copernicus
Download
Short summary
We describe a method of using remote sensing of the refractive index to determine the relative contribution of carbonaceous aerosols and absorbing iron minerals. Monthly climatologies of fine mode soot carbon are low for West Africa and the Middle East, but the southern Africa and South America biomass burning sites have peak values that are much higher; this is consistent with expectations. Hence, refractive index is a practical parameter for quantifying soot carbon in the atmosphere.
We describe a method of using remote sensing of the refractive index to determine the relative...
Citation
Share