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Retrieval of total NO2columns using Direct-Sun DOAS
measurements in Thessaloniki
Dimitrios Nikolis 1, Dimitris Karagkiozidis 1and Alkiviadis F. Bais 1
1 Laboratory of Atmospheric Physics, Physics Department, Aristotle University of Thessaloniki, Greece; dnikolis@auth.gr; dkaragki@auth.gr; abais@auth.gr
Introduction
In this work, the direct-sun DOAS (DS-DOAS) technique is used for the retrieval of total NO2column amounts. This
technique has proven to be accurate for deriving NO2concentrations from ground-based instruments using
measurements of direct solar irradiance, where the Air Mass Factor is approximated by the secant of the solar
zenith angle (SZA), as discussed in the Data and Methodology section. The DS-DOAS method is equally sensitive to
stratospheric and tropospheric NO2concentrations. It does not require complicated radiative transfer calculations,
is not affected by the Ring effect, does not require prior knowledge of ground reflectivity, nor the assumption of
horizontal homogeneity (except for large SZA), typical of zenith-sky DOAS and MAXDOAS.
The Delta system
A new research-grade MAX-DOAS instrument, Delta, was
developed at the Laboratory of Atmospheric Physics in
collaboration with the Royal Belgian Institute for Space
Aeronomy (BIRA-IASB), in the framework of the
PANhellenic infrastructure for Atmospheric Composition
and Climate Change (PANACEA) project. Delta is
characterized by increased sensitivity and accuracy in
measuring trace gases and aerosols, providing valuable
insights into air quality and atmospheric chemistry.
The Pandora system
The Pandora 2S instrument was designed from a
collaboration of the National Aeronautics and Sp ace
Administration (NASA) and the European Space
Agency (ESA) with SciGlob to address the gap in air
quality validation of satellite measurements. It is an
easy-to-deploy, ground-based system that monitors
various atmospheric trace gases absorbing in the
UV and visible spectral ranges, such as NO2, O3and
formaldehyde (HCHO).
RESULTS
•The comparison of the total NO2vertical column densities between the Pandora
and the Delta systems shows a good agreement, taking into account that the
two systems are completely independent.
•The achieved agreement suggests that the Delta system is reliable regarding its
setup and operation, and, along with other products, it can be used to reliably
monitor the NO2total column amounts in Thessaloniki.
Conclusions
❖Histogram of RMSE of NO2relative slant columns
Data with Root Mean Square Errors greater than 2 are excluded
to achieve a better performance of the method. The reason for
selecting a value of 2is because it excludes the 10%of the data
with the greatest errors.
References
1.Cede, A.; Herman, J.; Richter, A.; Krotkov, N.; Burrows, J. Measurements of Nitrogen Dioxide Total Column Amounts Using a Brewer Double Spectrophotometer in Direct Sun Mode. J. Geophys. Res. 2006, 111, D05304. https://doi.org/10.1029/2005JD006585.
2.Saiz-Lopez, A.; Saunders, R.W.; Joseph, D.M.; Ashworth, S.H.; Plane, J.M. Absolute Absorption Cross-Section and Photolysis Rate of I2. Atmos. Chem. Phys. 2004, 4, 1443–1450. https://doi.org/10.5194/acp-4-1443-2004.
16th International Conference on Meteorology,
Climatology and Atmospheric Physics –COMECAP
2023, 25-29 September 2023, Athens, Greece
❖Reference spectrum
The slant column density in the reference spectrum was
calculated with the Bootstrap Estimation method. Then, by
the following equation the absolute slant column SC at time
i can be calculated.
Results and Discussion
❖Calculation and comparison of the absolute total VCDs
The total slant column density for the Delta system SCTOTD is derived from the equation:
where:
Finally, the absolute total vertical column is given by: