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.