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Retrieval of Total NO2 Columns Using Direct-Sun Differential Optical Absorption Spectroscopy Measurements in Thessaloniki

Authors:
Dimitrios Nikolis at Aristotle University of Thessaloniki
Dimitrios Nikolis
Dimitris Karagkiozidis at Aristotle University of Thessaloniki
Dimitris Karagkiozidis
Alkiviadis F Bais at Aristotle University of Thessaloniki
Alkiviadis F Bais
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Citation: Nikolis, D.; Karagkiozidis,
D.; Bais, A.F. Retrieval of Total NO2
Columns Using Direct-Sun
Differential Optical Absorption
Spectroscopy Measurements in
Thessaloniki. Environ. Sci. Proc. 2023,
26, 51. https://doi.org/10.3390/
environsciproc2023026051
Academic Editors: Konstantinos
Moustris and Panagiotis Nastos
Published: 25 August 2023
Copyright: © 2023 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
Proceeding Paper
Retrieval of Total NO2Columns Using Direct-Sun Differential
Optical Absorption Spectroscopy Measurements
in Thessaloniki †
Dimitrios Nikolis *, Dimitris Karagkiozidis and Alkiviadis F. Bais
Laboratory of Atmospheric Physics, Physics Department, Aristotle University of Thessaloniki,
54124 Thessaloniki, Greece; dkaragki@auth.gr (D.K.); abais@auth.gr (A.F.B.)
*Correspondence: dnikolis@auth.gr
†Presented at the 16th International Conference on Meteorology, Climatology and Atmospheric
Physics—COMECAP 2023, Athens, Greece, 25–29 September 2023.
Abstract:
The monitoring of trace gases in the troposphere has been routinely performed at the
Laboratory of Atmospheric Physics, Thessaloniki, Greece, for a decade now, by multiple Multi-Axis
Differential Optical Absorption Spectroscopy (MAX-DOAS) instruments. Even though measurements
of trace gas concentrations in the troposphere are of great interest in terms of air quality, the MAX-
DOAS technique is only sensitive to absorbers in the lowest few kilometers of the atmosphere. In
this work, we present a methodology for the retrieval of total NO
2
columns in the atmosphere by
applying the DOAS technique on direct sun spectra (DS-DOAS) measured with a new research-grade
system. The advantages and limitations of the total NO
2
retrieval methodology, based on DS-DOAS,
are discussed. The accuracy and the quality of the retrieved columns were assessed by comparison
with a collocated Pandora system that also measures total NO
2
column amounts using a similar
technique with independent calibration.
Keywords: MAX-DOAS; Pandora; NO2total column; DS-DOAS
1. Introduction
Nitrogen dioxide (NO
2
) is a major pollutant worldwide, playing a key role in the
tropospheric and stratospheric chemistry [
1
]. It partly affects the ozone (O
3
) distribution in
the Earth’s atmosphere through contribution to the catalytic destruction of ozone in the
upper troposphere and lower stratosphere [
2
]. In the lower troposphere (mostly in the
boundary layer), the horizontal and vertical distributions of NO
2
strongly affect the air
quality and, consequently, human health [3].
Retrievals of total vertical column amount of NO
2
from space-borne sensors are
usually performed by applying Differential Optical Absorption Spectroscopy (DOAS) on
radiance measurements of scattered sunlight [
4
]. Concerning the ground-based systems,
sky radiances are measured either in the zenith direction (zenith-sky DOAS) [
5
] or in
multiple directions (MAX-DOAS) [6].
In this work, the direct-sun DOAS (DS-DOAS) technique was used for the retrieval
of total NO
2
column amounts. This technique has proven to be accurate for deriving
NO
2
concentrations from ground-based instruments using measurements of direct solar
irradiance [
7
], 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 NO
2
concentrations. It does not
require complicated radiative transfer calculations, is not affected by the Ring effect, does
not require prior knowledge of ground reflectivity [
7
], nor the assumption of horizontal
homogeneity (except for large SZA), typical of zenith-sky DOAS and MAXDOAS.
Environ. Sci. Proc. 2023,26, 51. https://doi.org/10.3390/environsciproc2023026051 https://www.mdpi.com/journal/environsciproc
Environ. Sci. Proc. 2023,26, 51 2 of 6
2. Instrumentation
A new research-grade MAX-DOAS instrument, Delta, was developed at the Labora-
tory of Atmospheric Physics in collaboration with the Royal Belgian Institute for Space
Aeronomy (BIRA-IASB), in the framework of the PANhellenic infrastructure for Atmo-
spheric 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. Delta consists of two sepa-
rate units: The external unit houses the optical head which is mounted on a sun tracker
that allows accurate orientation of the optics at different viewing directions. The Delta
system’s internal unit consists of a spectrograph that analyzes the incoming radiation and
produces a spectrum and a CCD camera that functions as a detector and measures the
spectral intensity. Both are placed in a thermally isolated box, designed by Raymetrics
S.A. (https://raymetrics.com, accessed on 25 March 2023), where the temperature is kept
constant at 20 ◦C with a thermoelectric Peltier system.
The Pandora 2S instrument was designed from a collaboration of the National Aero-
nautics and Space 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 NO
2
, O
3
and formaldehyde (HCHO). The
Pandora 2S Head sensor is mounted on a microprocessor-controlled azimuth and elevation
sun tracker and can point in any direction in the sky. The control software (Blick Software
Suite 1.8) supports automated measurements, remote monitoring and data transfers over
the internet. Pandora system’s internal unit consists of a controller running the BlickO
1.8 operating software under Microsoft Windows 10 Pro, the power distribution and system
interface electronics unit and the two spectrometers (UV/Vis and Vis/NIR). All these
components are installed to a thermally isolated box.
3. Data and Methodology
The Pandora direct-sun total NO2column data were produced using Pandora’s stan-
dard NO
2
algorithm implemented in the BlickP 1.8 software [
8
]. The measured direct-sun
spectra in the range of 400–440 nm were used in the analysis. The reference spectrum is a
synthetic reference spectrum, which is usually the average over several spectra measured
by the Pandora unit and corrected for the estimated total optical depth of the different
atmospheric extinction processes included in it.
Two spectral fittings were applied to the data, which differ in the effective temperature
of NO
2
absorption. In one case, the NO
2
cross section is taken for the boundary layer
temperature climatology and for the stratospheric temperature climatology in the other
case. For the final NO
2
total column product, an effective height for the stratosphere and a
stratospheric NO2climatology are used to estimate the stratospheric NO2fraction.
A direct-sun NO
2
inversion method, similar to that described in [
7
], was applied to
the radiances measured by the Delta system. These measurements were analyzed using
the QDOAS (version 3.2, September 2017) spectral fitting software suite developed by
BIRA-IASB (https://uv-vis.aeronomie.be/software/QDOAS/, accessed on 12 May 2023)
to derive the slant column density (SC) of NO
2
relative to a reference spectrum. The
measured relative slant columns SCRELi at time i would be given by the linear relation:
SCRELi = SCi−SCREF (1)
where SCiis the absolute slant column at time i.
The reference spectrum that is used in the DOAS analysis is a direct-sun spectrum
recorded around noon during a summer day under low NO
2
conditions (12/07/2022).
The slant column density in the reference spectrum was calculated with the Bootstrap
Estimation method [9] which will be discussed in the Results section.
Environ. Sci. Proc. 2023,26, 51 3 of 6
From the SC, the vertical column density (VC) is calculated by division with the
appropriate airmass factor. For the calculation of the direct-sun air mass factor, we use
Equation (2):
AMF = sec{arcsin[(r/(r + hEFF)) sin(SZAa)]} (2)
where r is the distance from the center of the Earth to the measurement location
(~6370 km
),
SZAa is the apparent solar zenith angle (i.e., the true SZA corrected for refraction), and
h
EFF
is the assumed effective height of the NO
2
layer. Here, we assume h
EFF
= 25 km to
derive the stratospheric AMFs and hEFF = 12.5 km for the total column AMF.
The absorption cross sections used are the same with those used in Pandora’s data
analysis [
10
] for NO
2
effective temperatures of 220, 298 and 254.5 K, which are represen-
tative for the stratospheric, tropospheric and total NO
2
columns, respectively. The other
atmospheric gases’ absorption cross sections used are for O
3
at 223 K [
11
], H
2
O at 293 K,
O4at 262 K [12], OIO at 298 K [13] and I2at 295 K [14].
4. Results
To calculate the total VC from the Delta system measurements, it is essential that
the SC of the reference spectrum is calculated. The method applied to perform this is the
Bootstrap Estimation method [
14
]. 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
2 is because it excludes the 10% of the data with the greatest errors, as can be seen in the
histogram in Figure 1.
Environ. Sci. Proc. 2023, 26, x 3 of 7
The reference spectrum that is used in the DOAS analysis is a direct-sun spectrum
recorded around noon during a summer day under low NO2 conditions (12/07/2022). The
slant column density in the reference spectrum was calculated with the Bootstrap Estima-
tion method [9] which will be discussed in the Results section.
From the SC, the vertical column density (VC) is calculated by division with the ap-
propriate airmass factor. For the calculation of the direct-sun air mass factor, we use Equa-
tion (2):
AMF = sec{arcsin[(r/(r + hEFF)) sin(SZAa)]} (2)
where r is the distance from the center of the Earth to the measurement location (~6370
km), SZAa is the apparent solar zenith angle (i.e., the true SZA corrected for refraction),
and hEFF is the assumed effective height of the NO2 layer. Here, we assume hEFF = 25 km to
derive the stratospheric AMFs and hEFF = 12.5 km for the total column AMF.
The absorption cross sections used are the same with those used in Pandora’s data
analysis [10] for NO2 effective temperatures of 220, 298 and 254.5 K, which are representa-
tive for the stratospheric, tropospheric and total NO2 columns, respectively. The other at-
mospheric gases’ absorption cross sections used are for O3 at 223 K [11], H2O at 293 K, O4
at 262 K [12], OIO at 298 K [13] and I2 at 295 K [14].
4. Results
To calculate the total VC from the Delta system measurements, it is essential that the
SC of the reference spectrum is calculated. The method applied to perform this is the Boot-
strap Estimation method [14]. Data with Root Mean Square Errors greater than 2 are ex-
cluded to achieve a better performance of the method. The reason for selecting a value of
2 is because it excludes the 10% of the data with the greatest errors, as can be seen in the
histogram in Figure 1.
Figure 1. Histogram of RMSE of NO2 relative slant columns measured by Delta and analyzed
through QDOAS 3.2 software.
For the Bootstrap method, the relative slant columns are binned with respect to AMFs
and the average of the lowest 2nd percentile in each bin is plotted against the correspond-
ing AMFs. The bin size was chosen to be 0.4 units of AMFs. The slant column density of
the reference day, SCREF = 7.65 Pmolec/cm2, is derived from the linear fit of the 2nd per-
centile averages and the corresponding AMFs (see Figure 2) as the intercept of the regres-
sion line.
Figure 1.
Histogram of RMSE of NO
2
relative slant columns measured by Delta and analyzed through
QDOAS 3.2 software.
For the Bootstrap method, the relative slant columns are binned with respect to AMFs
and the average of the lowest 2nd percentile in each bin is plotted against the corresponding
AMFs. The bin size was chosen to be 0.4 units of AMFs. The slant column density of the
reference day, SC
REF
= 7.65 Pmolec/cm
2
, is derived from the linear fit of the 2nd percentile
averages and the corresponding AMFs (see Figure 2) as the intercept of the regression line.
Environ. Sci. Proc. 2023,26, 51 4 of 6
Environ. Sci. Proc. 2023, 26, x 4 of 7
Figure 2. Relative NO2 slant columns SCREL as a function of AMFs for Delta. The green dots are the
2nd percentile minima of each of the 5 AMF bins and the red line is the respective linear regression.
The total slant column density for the Delta system SCTOTD is derived from Equation
(3):
SCTOTD = SCTD [(1 − qCLIM × AMFS)/SCSD] + AMFS × qCLIM + SCREF (3)
where SCTD and SCSD are, respectively, the tropospheric and stratospheric slant columns
from the Delta system and AMFS are calculated assuming that most of the absorption oc-
curs due to the stratospheric NO2. Finally, qCLIM represents the climatological value of the
stratospheric NO2 column for the location, season and time of each measurement.
The SCTD and SCSD are derived from the QDOAS analysis using cross sections for the
climatological temperatures of the troposphere (298 K) and the stratosphere (220 K), re-
spectively. Essentially, Equation (3) partitions the tropospheric and stratospheric columns
to the total column of NO2 under the assumption that the stratospheric column remains
close to the climatological values. Finally, the absolute total vertical column is calculated
for the Delta system:
VCTOTD = SCTOTD/AMFTOT (4)
where AMFTOT is the AMF calculated for the effective height 12.5 km, which is assumed
to be representative of the total NO2 column.
The comparison of the absolute total VCDs from the two systems is visualized in
Figure 3. In Figure 4, the differences between the absolute total vertical column amounts
from the two systems are shown.
Figure 2.
Relative NO
2
slant columns SC
REL
as a function of AMFs for Delta. The green dots are the
2nd percentile minima of each of the 5 AMF bins and the red line is the respective linear regression.
The total slant column density for the Delta system SC
TOTD
is derived from Equation (3):
SCTOTD = SCTD [(1 −qCLIM ×AMFS)/SCSD] + AMFS×qCLIM + SCREF (3)
where SC
TD
and SC
SD
are, respectively, the tropospheric and stratospheric slant columns
from the Delta system and AMF
S
are calculated assuming that most of the absorption
occurs due to the stratospheric NO
2
. Finally, q
CLIM
represents the climatological value of
the stratospheric NO2column for the location, season and time of each measurement.
The SC
TD
and SC
SD
are derived from the QDOAS analysis using cross sections for
the climatological temperatures of the troposphere (298 K) and the stratosphere (220 K),
respectively. Essentially, Equation (3) partitions the tropospheric and stratospheric columns
to the total column of NO
2
under the assumption that the stratospheric column remains
close to the climatological values. Finally, the absolute total vertical column is calculated
for the Delta system:
VCTOTD = SCTOTD/AMFTOT (4)
where AMF
TOT
is the AMF calculated for the effective height 12.5 km, which is assumed to
be representative of the total NO2column.
The comparison of the absolute total VCDs from the two systems is visualized in
Figure 3. In Figure 4, the differences between the absolute total vertical column amounts
from the two systems are shown.
The comparison of the total NO
2
absolute vertical columns measured by the two
systems reveals generally a very good correlation (R
≈
0.97), with a few outliers. The slope
of the linear regression was very close to the ideal value of 1 (1.009) and the offset was close
to 0.1 Pmolec/cm
2
. The points deviating from the ideal line are due to residual noise in
the retrieval algorithms and instrumental noise and uncertainties. The distribution of the
differences peaks very close to 0.1, which can be explained by the offset value, indicates
that more than 95% of the measurements agree to within 0.1 Pmolec/cm2.
Environ. Sci. Proc. 2023,26, 51 5 of 6
Environ. Sci. Proc. 2023, 26, x 5 of 7
Figure 3. The comparison between absolute total VCDs from Delta and Pandora systems.
Figure 4. The total NO2 VCDs differences between the Delta and the Pandora systems (in
Pmolec/cm2).
The comparison of the total NO2 absolute vertical columns measured by the two sys-
tems reveals generally a very good correlation (R ≈ 0.97), with a few outliers. The slope of
the linear regression was very close to the ideal value of 1 (1.009) and the offset was close
to 0.1 Pmolec/cm2. The points deviating from the ideal line are due to residual noise in the
retrieval algorithms and instrumental noise and uncertainties. The distribution of the dif-
ferences peaks very close to 0.1, which can be explained by the offset value, indicates that
more than 95% of the measurements agree to within 0.1 Pmolec/cm2.
5. Conclusions
A methodology for the calculation of the total NO2 column density for a research-
grade DOAS system (Delta) operating in Thessaloniki at the Laboratory of Atmospheric
Physics, AUTH, was presented. The data from this system were compared to data from a
collocated Pandora system that has been operating since September 2022. The comparison
of the total ΝΟ2 vertical column densities between the Pandora and the Delta systems
shows a good agreement, taking into account that the two systems are completely inde-
pendent. As the Pandora system has been validated before delivery in the frame of the
Pandonia Global Network, their achieved agreement suggests that the Delta system is
Figure 3. The comparison between absolute total VCDs from Delta and Pandora systems.
Environ. Sci. Proc. 2023, 26, x 5 of 7
Figure 3. The comparison between absolute total VCDs from Delta and Pandora systems.
Figure 4. The total NO2 VCDs differences between the Delta and the Pandora systems (in
Pmolec/cm2).
The comparison of the total NO2 absolute vertical columns measured by the two sys-
tems reveals generally a very good correlation (R ≈ 0.97), with a few outliers. The slope of
the linear regression was very close to the ideal value of 1 (1.009) and the offset was close
to 0.1 Pmolec/cm2. The points deviating from the ideal line are due to residual noise in the
retrieval algorithms and instrumental noise and uncertainties. The distribution of the dif-
ferences peaks very close to 0.1, which can be explained by the offset value, indicates that
more than 95% of the measurements agree to within 0.1 Pmolec/cm2.
5. Conclusions
A methodology for the calculation of the total NO2 column density for a research-
grade DOAS system (Delta) operating in Thessaloniki at the Laboratory of Atmospheric
Physics, AUTH, was presented. The data from this system were compared to data from a
collocated Pandora system that has been operating since September 2022. The comparison
of the total ΝΟ2 vertical column densities between the Pandora and the Delta systems
shows a good agreement, taking into account that the two systems are completely inde-
pendent. As the Pandora system has been validated before delivery in the frame of the
Pandonia Global Network, their achieved agreement suggests that the Delta system is
Figure 4.
The total NO
2
VCDs differences between the Delta and the Pandora systems (in
Pmolec/cm2).
5. Conclusions
A methodology for the calculation of the total NO
2
column density for a research-grade
DOAS system (Delta) operating in Thessaloniki at the Laboratory of Atmospheric Physics,
AUTH, was presented. The data from this system were compared to data from a collocated
Pandora system that has been operating since September 2022. The comparison of the total
NO
2
vertical column densities between the Pandora and the Delta systems shows a good
agreement, taking into account that the two systems are completely independent. As the
Pandora system has been validated before delivery in the frame of the Pandonia Global
Network, their 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.
Author Contributions:
Conceptualization, D.N., D.K. and A.F.B.; methodology, D.N. and A.F.B.;
writing—original draft preparation, D.N.; writing—review and editing, D.K. and A.F.B.; visualization,
D.N.; supervision, A.F.B. All authors have read and agreed to the published version of the manuscript.
Funding: This research received no external funding.
Environ. Sci. Proc. 2023,26, 51 6 of 6
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement:
The data presented in this study are available on request from the
corresponding author. The data are not publicly available because they are preliminary retrievals.
Acknowledgments:
The authors acknowledge Thomas Danckaert (thomas.danckaert@aeronomie.be),
Caroline Fayt (caroline.fayt@aeronomie.be) and Michel Van Roozendael (michelv@aeronomie.be) for
providing the QDOAS 3.2 software.
Conflicts of Interest: The authors declare no conflict of interest.
References
1.
Crutzen, P.J.; Heidt, L.E.; Krasnec, J.P.; Pollock, W.H.; Seiler, W. Biomass Burning as a Source of Atmospheric Gases CO, H
2
, N
2
O,
NO, CH3Cl and COS. Nature 1979,282, 253–256. [CrossRef]
2.
Brasseur, G.P.; Cox, R.A.; Hauglustaine, D.; Isaksen, I.; Lelieveld, J.; Lister, D.H.; Sausen, R.; Schumann, U.; Wahner, A.; Wiesen, P.
European Scientific Assessment of the Atmospheric Effects of Aircraft Emissions. Atmos. Environ.
1998
,32, 2329–2418. [CrossRef]
3.
Air Quality in Europe 2022—European Environment Agency, Web Report. Available online: https://www.eea.europa.eu/
publications/air-quality-in-europe-2022 (accessed on 10 May 2023).
4. Platt, U.; Stutz, J. Differential Optical Absorption Spectroscopy; Springer: Berlin/Heidelberg, Germany, 2008. [CrossRef]
5.
Liley, J.B.; Johnston, P.V.; McKenzie, R.L.; Thomas, A.J.; Boyd, I.S. Stratospheric NO
2
Variations from a Long Time Series at Lauder,
New Zealand. J. Geophys. Res. Atmos. 2000,105, 11633–11640. [CrossRef]
6.
Hönninger, G.; Von Friedeburg, C.; Platt, U. Multi Axis Differential Optical Absorption Spectroscopy (MAX-DOAS). Atmos. Chem.
Phys. 2004,4, 231–254. [CrossRef]
7.
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. [CrossRef]
8.
Zhao, X.; Griffin, D.; Fioletov, V.; McLinden, C.; Davies, J.; Ogyu, A.; Lee, S.C.; Lupu, A.; Moran, M.D.; Cede, A.; et al. Retrieval of
Total Column and Surface NO2from Pandora Zenith-Sky Measurements. Atmos. Chem. Phys. 2019,19, 10619–10642. [CrossRef]
9.
Herman, J.; Cede, A.; Spinei, E.; Mount, G.; Tzortziou, M.; Abuhassan, N. NO
2
Column Amounts from Ground-Based Pandora
and MFDOAS Spectrometers Using the Direct-Sun DOAS Technique: Intercomparisons and Application to OMI Validation. J.
Geophys. Res. 2009,114, D13307. [CrossRef]
10.
Vandaele, A.C.; Hermans, C.; Simon, P.C.; Carleer, M.; Colin, R.; Fally, S.; Merienne, M.F.; Jenouvrier, A.; Coquart, B. Measurements
of the NO
2
Absorption Cross-Section from 42 000 cm
−1
to 10 000 cm
−1
(238–1000 Nm) at 220 K and 294 K. J. Quant. Spectrosc.
Radiat. Transf. 1998,59, 171–184. [CrossRef]
11.
Bogumil, K.; Orphal, J.; Homann, T.; Voigt, S.; Spietz, P.; Fleischmann, O.C.; Vogel, A.; Hartmann, M.; Kromminga, H.;
Bovensmann, H.; et al. Measurements of Molecular Absorption Spectra with the SCIAMACHY Pre-Flight Model: Instrument
Characterization and Reference Data for Atmospheric Remote-Sensing in the 230–2380 Nm Region. J. Photochem. Photobiol. A
Chem. 2003,157, 167–184. [CrossRef]
12.
Thalman, R.; Volkamer, R. Temperature Dependent Absorption Cross-Sections of O
2
–O
2
Collision Pairs between 340 and 630 Nm
and at Atmospherically Relevant Pressure. Phys. Chem. Chem. Phys. 2013,15, 15371–15381. [CrossRef] [PubMed]
13.
Spietz, P.; Martín, J.C.; Burrows, J.P. Spectroscopic Studies of the I
2
/O
3
Photochemistry: Part 2. Improved Spectra of Iodine
Oxides and Analysis of the IO Absorption Spectrum. J. Photochem. Photobiol. A Chem. 2005,176, 50–67. [CrossRef]
14.
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. [CrossRef]
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Absolute absorption cross-section and photolysis rate of I2
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Following recent observations of molecular iodine (I2) in the coastal marine boundary layer (MBL) (Saiz-Lopez and Plane, 2004), it has become important to determine the absolute absorption cross-section of I2 at reasonably high resolution, and also to evaluate the rate of photolysis of the molecule in the lower atmosphere. The absolute absorption cross-section (σ) of gaseous I2 at room temperature and pressure (295K, 760Torr) was therefore measured between 182 and 750nm using a Fourier Transform spectrometer at a resolution of 4cm-1 (0.1nm at λ=500nm). The maximum absorption cross-section in the visible region was observed at λ=533.0nm to be σ=(4.24±0.50)x10-18cm2molecule-1. The spectrum is available as supplementary material accompanying this paper. The photo-dissociation rate constant (J) of gaseous I2 was also measured directly in a solar simulator, yielding J(I2)=0.12±0.03s-1 for the lower troposphere. This is in excellent agreement with the value of 0.12±0.015s-1 calculated using the measured absorption cross-section, terrestrial solar flux for clear sky conditions and assuming a photo-dissociation yield of unity. A two-stream radiation transfer model was then used to determine the variation in photolysis rate with solar zenith angle (SZA), from which an analytic expression is derived for use in atmospheric models. Photolysis appears to be the dominant loss process for I2 during daytime, and hence an important source of iodine atoms in the lower atmosphere.
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Full-text available
Pandora spectrometers can retrieve nitrogen dioxide (NO2) vertical column densities (VCDs) via two viewing geometries: direct Sun and zenith sky. The direct-Sun NO2 VCD measurements have high quality (0.1 DU accuracy in clear-sky conditions) and do not rely on any radiative transfer model to calculate air mass factors (AMFs); however, they are not available when the Sun is obscured by clouds. To perform NO2 measurements in cloudy conditions, a simple but robust NO2 retrieval algorithm is developed for Pandora zenith-sky measurements. This algorithm derives empirical zenith-sky NO2 AMFs from coincident high-quality direct-Sun NO2 observations. Moreover, the retrieved Pandora zenith-sky NO2 VCD data are converted to surface NO2 concentrations with a scaling algorithm that uses chemical-transport-model predictions and satellite measurements as inputs. NO2 VCDs and surface concentrations are retrieved from Pandora zenith-sky measurements made in Toronto, Canada, from 2015 to 2017. The retrieved Pandora zenith-sky NO2 data (VCD and surface concentration) show good agreement with both satellite and in situ measurements. The diurnal and seasonal variations of derived Pandora zenith-sky surface NO2 data also agree well with in situ measurements (diurnal difference within ±2 ppbv). Overall, this work shows that the new Pandora zenith-sky NO2 products have the potential to be used in various applications such as future satellite validation in moderate cloudy scenes and air quality monitoring.
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Stratospheric NO2 variations from a long time series at Lauder, New Zealand
Article
Full-text available
  • May 2000
Eighteen years of NO2 measurements using zenith-scattered sunlight are analyzed for seasonal, cyclic, and episodic variability and secular trends. The analysis shows a marked increase in stratospheric NO2 over the period, corresponding to a trend of 5% per decade, and the influences of both the El Chichón and Pinatubo eruptions are clearly evident. Smaller effects of the El Niño-Southern Oscillation and quasi-biennial oscillation are apparent, but correlation with the solar cycle is poor after correction for autocorrelation. All of these effects are similar for sunrise and sunset NO2.
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European Scientific Assessment of the Atmospheric Effects of Aircraft Emission
Article
  • Jul 1998
  • ATMOS ENVIRON
The purpose of this report prepared on behalf of the European Commission is to review the current understanding of chemical and dynamical processes in the upper troposphere and lower stratosphere, and to assess how these processes could be perturbed as a result of current and future aircraft emissions. Specifically, perturbations in the atmospheric abundance of ozone and in climate forcing, as predicted by atmospheric models, will be presented. The goal is to compile and evaluate scientific information related to the atmospheric impact of subsonic and supersonic aircraft emissions and to review the state of knowledge concerning the various aspects of this problem. In Section 2, the issues and scientific questions relevant to the problem of aircraft perturbations will be presented. The key physical and chemical processes occurring in the troposphere and stratosphere will be discussed in Section 3. Estimates of air traffic and aircraft emissions will be given in Section 4. Section 5 and 6 will review the understanding of the atmospheric impact of aircraft emissions at small and large scale, respectively. The effect of aircraft emissions on climate forcing will be discussed in Section 7. Finally, conclusions will be provided in Section 8.
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Temperature dependent absorption cross-sections of O-2-O-2 collision pairs between 340 and 630 nm and at atmospherically relevant pressure
Article
  • Aug 2013
  • PHYS CHEM CHEM PHYS
The collisions between two oxygen molecules give rise to O4 absorption in the Earth atmosphere. O4 absorption is relevant to atmospheric transmission and Earth's radiation budget. O4 is further used as a reference gas in Differential Optical Absorption Spectroscopy (DOAS) applications to infer properties of clouds and aerosols. The O4 absorption cross section spectrum of bands centered at 343, 360, 380, 446, 477, 532, 577 and 630 nm is investigated in dry air and oxygen as a function of temperature (203-295 K), and at 820 mbar pressure. We characterize the temperature dependent O4 line shape and provide high precision O4 absorption cross section reference spectra that are suitable for atmospheric O4 measurements. The peak absorption cross-section is found to increase at lower temperatures due to a corresponding narrowing of the spectral band width, while the integrated cross-section remains constant (within <3%, the uncertainty of our measurements). The enthalpy of formation is determined to be ΔH(250) = -0.12 ± 0.12 kJ mol(-1), which is essentially zero, and supports previous assignments of O4 as collision induced absorption (CIA). At 203 K, van der Waals complexes (O2-dimer) contribute less than 0.14% to the O4 absorption in air. We conclude that O2-dimer is not observable in the Earth atmosphere, and as a consequence the atmospheric O4 distribution is for all practical means and purposes independent of temperature, and can be predicted with an accuracy of better than 10(-3) from knowledge of the oxygen concentration profile.
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Measurements of molecular absorption spectra with the SCIAMACHY pre-flight model: Instrument characterization and reference data for atmospheric remote-sensing in the 230-2380 nm region
Article
  • May 2003
  • J PHOTOCH PHOTOBIO A
Using the scanning imaging absorption spectrometer for atmospheric chartography (SCIAMACHY) pre-flight model satellite spectrometer, gas-phase absorption spectra of the most important atmospheric trace gases (O3, NO2, SO2, O2, OClO, H2CO, H2O, CO, CO2, CH4, and N2O) have been measured in the 230–2380nm range at medium spectral resolution and at several temperatures between 203 and 293K. The spectra show high signal-to-noise ratio (between 200 up to a few thousands), high baseline stability (better than 10−2) and an accurate wavelength calibration (better than 0.01nm) and were scaled to absolute absorption cross-sections using previously published data. The results are important as reference data for atmospheric remote-sensing and physical chemistry. Amongst other results, the first measurements of the Wulf bands of O3 up to their origin above 1000nm were made at five different temperatures between 203 and 293K, the first UV-Vis absorption cross-sections of NO2 in gas-phase equilibrium at 203K were recorded, and the ultraviolet absorption cross-sections of SO2 were measured at five different temperatures between 203 and 296K. In addition, the molecular absorption spectra were used to improve the wavelength calibration of the SCIAMACHY spectrometer and to characterize the instrumental line shape (ILS) and straylight properties of the instrument. It is demonstrated that laboratory measurements of molecular trace gas absorption spectra prior to launch are important for satellite instrument characterization and to validate and improve the spectroscopic database.
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Biomass burning as a source of atmospheric gases CO, H2_2, N2_2O, NO, CH3_3Cl and COS
Article
  • Nov 1979
The potential importance of deforestation and biomass burning for the atmospheric CO2 cycle has received much attention and caused some controversy. Biomass burning can contribute extensively to the budgets of several gases which are important in atmospheric chemistry. In several cases the emission is comparable to the technological source. Most burning takes place in the tropics in the dry season and is caused by man’s activities. The potential importance of deforestation and biomass burning for the atmospheric CO2 cycle has received much attention and caused some controversy. In this article we will show the probable importance of biomass burning as a trace gas source, which is caused by man’s activities in the tropics. We used the results of our global biomass burning analysis to derive some rough estimates of the sources of the important atmospheric trace gases CO, H2, CH4, N2O, NOx (NO and NO2), COS and CH3Cl from the worldwide burning of biomass.
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Differential Optical Absorption Spectroscopy (DOAS)—Principles and Applications
Book
  • Jan 2008
Measurement techniques form the basis of our knowledge about atmospheric composition and chemistry. Presently, important questions of atmospheric chemistry center on urban pollution, free-radical chemistry, degradation of greenhouse gases and the budgets of tropospheric and stratospheric ozone. Among the many different optical spectroscopic methods that are in use, DOAS has emerged as a universal technique to measure the concentrations of atmospheric trace gases by making use of the characteristic absorption features of gas molecules along a path of known length in the open atmosphere. This book reviews the basics of atmospheric chemistry, radiation transport, and optical spectroscopy before detailing the principles underlying DOAS. The second part of the book describes the design and application of DOAS instruments as well as the evaluation and interpretation of spectra. The recent expansion of DOAS application to the imaging of trace gas distributions by ground, aircraft, and satellite-based instruments is also covered. Written for graduate students and researchers with a general background in environmental physics, this book especially addresses the needs of those working in the field of atmospheric chemistry, pollution monitoring, and volcanology.
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NO2 column amounts from ground-based Pandora and MFDOAS spectrometers using the Direct-Sun DOAS technique: Intercomparisons and application to OMI validation
Article
  • Jul 2009
Vertical column amounts of nitrogen dioxide, C(NO2), are derived from ground-based direct solar irradiance measurements using two new and independently developed spectrometer systems, Pandora (Goddard Space Flight Center) and MFDOAS (Washington State University). We discuss the advantages of C(NO2) retrievals based on Direct Sun - Differential Optical Absorption Spectroscopy (DS-DOAS). The C(NO2) data are presented from field campaigns using Pandora at Aristotle University (AUTH), Thessaloniki, Greece; a second field campaign involving both new instruments at Goddard Space Flight Center (GSFC), Greenbelt, Maryland; a Pandora time series from December 2006 to October 2008 at GSFC; and a MFDOAS time series for spring 2008 at Pacific Northwest National Laboratory (PNNL), Richland, Washington. Pandora and MFDOAS were compared at GFSC and found to closely agree, with both instruments having a clear-sky precision of 0.01 DU (1 DU = 2.67 × 1016 molecules/cm2) and a nominal accuracy of 0.1 DU. The high precision is obtained from careful laboratory characterization of the spectrometers (temperature sensitivity, slit function, pixel to pixel radiometric calibration, and wavelength calibration), and from sufficient measurement averaging to reduce instrument noise. The accuracy achieved depends on laboratory-measured absorption cross sections and on spectrometer laboratory and field calibration techniques used at each measurement site. The 0.01 DU precision is sufficient to track minute-by-minute changes in C(NO2) throughout each day with typical daytime values ranging from 0.2 to 2 DU. The MFDOAS instrument has better noise characteristics for a single measurement, which permits MFDOAS to operate at higher time resolution than Pandora for the same precision. Because Pandora and MFDOAS direct-sun measurements can be made in the presence of light to moderate clouds, but with reduced precision (∼0.2 DU for moderate cloud cover), a nearly continuous record can be obtained, which is important when matching OMI overpass times for satellite data validation. Comparisons between Pandora and MFDOAS with OMI are discussed for the moderately polluted GSFC site, between Pandora and OMI at the AUTH site, and between MFDOAS and OMI at the PNNL site. Validation of OMI measured C(NO2) is essential for the scientific use of the satellite data for air quality, for atmospheric photolysis and chemistry, and for retrieval of other quantities (e.g., accurate atmospheric correction for satellite estimates of ocean reflectance and bio-optical properties). Changes in the diurnal variability of C(NO2) with season and day of the week are presented based on the 2-year time series at GSFC measured by the Pandora instrument.
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