Satellite-based evidence of wavelength-dependent aerosol absorption in biomass burning smoke inferred from Ozone Monitoring Instrument 1Department of Atmospheric & Planetary Sciences, Hampton University, Hampton, VA 23668, USA
25 Oct 2011
2NASA Goddard Space Flight Center, Greenbelt, MD, 20771, USA
Received: 15 Feb 2011 – Published in Atmos. Chem. Phys. Discuss.: 02 Mar 2011Abstract. We provide satellite-based evidence of the spectral dependence of absorption
in biomass burning aerosols over South America using near-UV measurements
made by the Ozone Monitoring Instrument (OMI) during 2005–2007. In the
current near-UV OMI aerosol algorithm (OMAERUV), it is implicitly assumed
that the only absorbing component in carbonaceous aerosols is black carbon
whose imaginary component of the refractive index is wavelength independent.
With this assumption, OMI-derived aerosol optical depth (AOD) is found to be
significantly over-estimated compared to that of AERONET at several sites
during intense biomass burning events (August-September). Other well-known
sources of error affecting the near-UV method of aerosol retrieval do not
explain the large observed AOD discrepancies between the satellite and the
ground-based observations. A number of studies have revealed strong spectral
dependence in carbonaceous aerosol absorption in the near-UV region
suggesting the presence of organic carbon in biomass burning generated
aerosols. A sensitivity analysis examining the importance of accounting for
the presence of wavelength-dependent aerosol absorption in carbonaceous
particles in satellite-based remote sensing was carried out in this work.
The results convincingly show that the inclusion of spectrally-dependent
aerosol absorption in the radiative transfer calculations leads to a more
accurate characterization of the atmospheric load of carbonaceous aerosols.
The use of a new set of aerosol models assuming wavelength-dependent aerosol
absorption in the near-UV region (Absorption Angstrom Exponent
λ−2.5 to −3.0) improved the OMAERUV retrieval results by significantly
reducing the AOD bias observed when gray aerosols were assumed. In addition,
the new retrieval of single-scattering albedo is in better agreement with
those of AERONET within the uncertainties (ΔSSA = ±0.03). The
new colored carbonaceous aerosol model was also found to reproduce the
ground-based AOD observations over the biomass burning region of central
Africa and northern India. Together with demonstrating a significant
improvement in the retrieval of aerosol properties from OMI, the present
study highlights the greater sensitivity of the near-UV measurements to the
varying spectral aerosol absorption. This capability can be explored further
for the use in the identification of the black carbon and organics in the
biomass burning aerosols.
Revised: 12 Sep 2011 – Accepted: 22 Sep 2011 – Published: 25 Oct 2011
Citation: Jethva, H. and Torres, O.: Satellite-based evidence of wavelength-dependent aerosol absorption in biomass burning smoke inferred from Ozone Monitoring Instrument, Atmos. Chem. Phys., 11, 10541-10551, doi:10.5194/acp-11-10541-2011, 2011.