In:
Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 21, No. 17 ( 2021-08-31), p. 12867-12894
Abstract:
Abstract. Ground-based Multi-AXis Differential Optical Absorption
Spectroscopy (MAX-DOAS) is a state-of-the-art remote sensing technique for
deriving vertical profiles of trace gases and aerosols. However, MAX-DOAS
profile inversions under aerosol pollution scenarios are challenging because
of the complex radiative transfer and limited information content of the
measurements. In this study, the performances of two inversion algorithms
were evaluated for various aerosol pollution scenarios based on synthetic
slant column densities (SCDs) derived from radiative transfer simulations.
Compared to previous studies, in our study, much larger ranges of aerosol optical depth (AOD) and
NO2 vertical column densities (VCDs) are covered. One inversion algorithm is based on optimal
estimation; the other uses a parameterized approach. In this analysis, three
types of profile shapes for aerosols and NO2 were considered:
exponential, Boltzmann, and Gaussian. First, the systematic deviations of
the retrieved aerosol profiles from the input profiles were investigated.
For most cases, the AODs of the retrieved profiles were found to be
systematically lower than the input values, and the deviations increased
with increasing AOD. In particular for the optimal estimation algorithm and for
high AOD, these findings are consistent with the results in previous studies.
The assumed single scattering albedo (SSA) and asymmetry parameter (AP) have a systematic
influence on the aerosol retrieval. However, for most cases the influence of
the assumed SSA and AP on the retrieval results are rather small (compared
to other uncertainties). For the optimal estimation algorithm, the agreement
with the input values can be improved by optimizing the covariance matrix of
the a priori uncertainties. Second, the aerosol effects on the NO2 profile
retrieval were tested. Here, especially for the optimal estimation
algorithm, a systematic dependence on the NO2 VCD was found, with a
strong relative overestimation of the retrieved results for low NO2
VCDs and an underestimation for high NO2 VCDs. In contrast, the
dependence on the aerosol profiles was found to be rather low.
Interestingly, the results for both investigated wavelengths (360 and 477 nm) were found to be rather similar, indicating that the differences in the
radiative transfer between both wavelengths have no strong effect. In
general, both inversion schemes can retrieve the near-surface values of
aerosol extinction and trace gas concentrations well.
Type of Medium:
Online Resource
ISSN:
1680-7324
DOI:
10.5194/acp-21-12867-2021
DOI:
10.5194/acp-21-12867-2021-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2021
detail.hit.zdb_id:
2092549-9
detail.hit.zdb_id:
2069847-1
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