The role of aerosol layer height in quantifying aerosol absorption from ultraviolet satellite observations
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Published:2019-12-02
Issue:12
Volume:12
Page:6319-6340
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ISSN:1867-8548
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Container-title:Atmospheric Measurement Techniques
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language:en
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Short-container-title:Atmos. Meas. Tech.
Author:
Sun JiyuntingORCID, Veefkind Pepijn, Nanda Swadhin, van Velthoven Peter, Levelt Pieternel
Abstract
Abstract. The purpose of this study is to demonstrate the role of
aerosol layer height (ALH) in quantifying the single scattering albedo (SSA)
from ultraviolet satellite observations for biomass burning aerosols. In the
first experiment, we retrieve SSA by minimizing the near-ultraviolet (near-UV) absorbing aerosol index (UVAI) difference between
observed values and those simulated by a radiative transfer model. With the
recently released S-5P TROPOMI ALH product constraining forward
simulations, a significant gap in the retrieved SSA (0.25) is found between
radiative transfer simulations with spectral flat aerosols and those with strong spectrally dependent aerosols, implying that inappropriate assumptions regarding aerosol absorption spectral dependence may cause severe misinterpretations
of the aerosol absorption. In the second part of this paper, we propose an
alternative method to retrieve SSA based on a long-term record of co-located satellite and ground-based measurements using the support vector regression
(SVR) approach. This empirical method is free from the uncertainties due to the
imperfection of a priori assumptions on aerosol microphysics seen in the
first experiment. We present the potential capabilities of SVR using
several fire events that have occurred in recent years. For all cases, the difference
between SVR-retrieved SSA and AERONET are generally within ±0.05, and
over half of the samples are within ±0.03. The results are encouraging,
although in the current phase the model tends to overestimate the SSA for
relatively absorbing cases and fails to predict SSA for some extreme
situations. The spatial contrast in SSA retrieved by radiative transfer
simulations is significantly higher than that retrieved by SVR, and the latter better
agrees with SSA from MERRA-2 reanalysis. In the future, more sophisticated
feature selection procedures and kernel functions should be taken into
consideration to improve the SVR model accuracy. Moreover, the high-resolution TROPOMI UVAI and co-located ALH products will guide us to more
reliable training data sets and more powerful algorithms to quantify aerosol
absorption from UVAI records.
Publisher
Copernicus GmbH
Subject
Atmospheric Science
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