Combining Multi-Wavelength AERONET SSA Retrievals with a MIE Model and
UV AI from OMI to Quantify the Global AAOD of BC and OC
Abstract
Black carbon (BC), organic carbon (OC) and dust (or Absorbing Aerosols -
AA) strongly absorb visible solar radiation, leading to impacts on the
atmospheric radiation budget, climate, water cycle, and more. Recent
attempts have been made to elucidate the spatial-temporal concentrations
and radiative forcing of AA over East Asia using the UV band OMAERUV
product from OMI. The product provides global coverage of AAOD in the UV
bands, limiting the results to where retrievals can be made, and to
cases where the average aerosol size is not too small. For these
reasons, this approach cannot estimate the magnitude of total AAOD
and/or radiative forcing. To achieve this, we include relevant data from
multiple bands in the visible and NIR in tandem with the UV, so that a
more complete relationship can be made to understand the magnitude and
properties of AA globally. We employ a MIE model to simulate the
absorption of core-shell coated mixtures of AA (specifically a mixture
of BC core with sulfate shell (MBS) and OC core with sulfate shell (MOS)
across multiple individual wavelengths. These values are then merged
with individual inversions of SSA from AERONET at each individual
wavelength across the spectrum from the UV through the NIR. Fitting is
done based on the temporally varying magnitude band of the measured AOD
and the inverted SSA incorporating all individual data points where both
calculations exist at each station, from 2010 to 2016. The relationship
between core and shell sizes that is consistent with AERONET is then
fitted to OMI measurements that overlap AERONET in space and time. A
sensitivity matrix of optical uncertainties is made to compute the
robustness of the constrained aerosol size, chemical composition and
refractive indices. Initial results show that retrieved aerosol
properties of MBS and MOS are consistent with known properties over
urban areas, biomass burning areas, and those regions frequently
impacted by long-range transport events, as observed over Asia. A few
interesting scientific findings include mixing between these different
sources and detection of otherwise missing sources. It is hoped that
ongoing calculations allowing our approximation to be extended spatially
away from sites where AERONET measurements exist will also be ready to
present.