Retrieval of tropospheric aerosol, NO<sub>2</sub> and HCHO vertical profiles from MAX-DOAS observations over Thessaloniki, Greece

Abstract. In this study we focus on the retrieval of aerosol and trace gas vertical profiles from Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) observations for the first time over Thessaloniki, Greece. We use two independent inversion algorithms for the profile retrievals: The Mexican MAX-DOAS Fit (MMF) and the Mainz Profile Algorithm (MAPA). The former is based on the Optimal Estimation Method (OEM), while the latter follows a parameterization approach. We evaluate the performance of MMF and MAPA and we validate their retrieved products with ancillary data measured by other co-located reference instruments. We find an excellent agreement between the tropospheric column densities of NO2 retrieved by MMF and MAPA (Slope = 1.009, Pearson's correlation coefficient R = 0.982) and a good correlation for the case of HCHO (R = 0.927). For aerosols, we find better agreement for the aerosol optical depths (AODs) in the visible (i.e., at 477 nm), compared to the UV (360 nm) and we show that the agreement strongly depends on the O4 scaling factor that is used in the analysis. The trace gas differential slant column densities (dSCDs), simulated by the forward models, are also in good agreement, except for HCHO, where larger scatter is observed due to the increased spectral noise of the measurements in the UV. The agreement for NO2 and HCHO surface concentrations is similar to the comparison of the integrated columns with slightly decreased correlation coefficients. The AODs retrieved by the MAX-DOAS are validated by comparing them with AOD values measured by a CIMEL sun-photometer and a Brewer spectrophotometer. Four different flagging schemes were applied to the data in order to evaluate their performance. Qualitatively, a generally good agreement is observed for both wavelengths, but we find a systematic bias from the CIMEL and Brewer measurements, due to the limited sensitivity of the MAX-DOAS in retrieving information at higher altitudes, especially in the UV. An in-depth validation of the aerosol vertical profiles retrieved by the MAX-DOAS is not possible since only in very few cases the true aerosol profile is known during the period of study. However, we examine four cases, where the MAX-DOAS provided a generally good estimation of the shape of the profiles retrieved by a co-located multi-wavelength lidar system. The NO2 surface concentrations are validated against in situ observations and the comparison of both MMF and MAPA revealed good agreement with correlation coefficients of R = 0.78 and R = 0.73, respectively. Finally, the effect of the O4 scaling factor is investigated by intercomparing the integrated columns retrieved by the two algorithms and also by comparing the AODs derived by MAPA for different values of the scaling factor with AODs measured by the CIMEL and the Brewer.

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The Mainz profile algorithm (MAPA)

Atmospheric Measurement Techniques ◽

10.5194/amt-12-1785-2019 ◽

2019 ◽

Vol 12 (3) ◽

pp. 1785-1806 ◽

Cited By ~ 7

Author(s):

Steffen Beirle ◽

Steffen Dörner ◽

Sebastian Donner ◽

Julia Remmers ◽

Yang Wang ◽

...

Keyword(s):

A Priori ◽

Scaling Factor ◽

Least Square ◽

Trace Gas ◽

Vertical Profiles ◽

Mixing Ratios ◽

Surface Mixing ◽

Sensitivity Studies ◽

The Impact ◽

Good Agreement

Abstract. The Mainz profile algorithm (MAPA) derives vertical profiles of aerosol extinction and trace gas concentrations from MAX-DOAS measurements of slant column densities under multiple elevation angles. This paper presents (a) a detailed description of the MAPA (v0.98), (b) results for the CINDI-2 campaign, and (c) sensitivity studies on the impact of a priori assumptions such as flag thresholds. Like previous profile retrieval schemes developed at MPIC, MAPA is based on a profile parameterization combining box profiles, which also might be lifted, and exponential profiles. But in contrast to previous inversion schemes based on least-square fits, MAPA follows a Monte Carlo approach for deriving those profile parameters yielding best match to the MAX-DOAS observations. This is much faster and directly provides physically meaningful distributions of profile parameters. In addition, MAPA includes an elaborated flagging scheme for the identification of questionable or dubious results. The AODs derived with MAPA for the CINDI-2 campaign show good agreement with AERONET if a scaling factor of 0.8 is applied for O4, and the respective NO2 and HCHO surface mixing ratios match those derived from coincident long-path DOAS measurements. MAPA results are robust with respect to modifications of the a priori MAPA settings within plausible limits.

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Intercomparison of MAX-DOAS Vertical Profile Retrieval Algorithms: Studies using Synthetic Data

10.5194/amt-2018-423 ◽

2018 ◽

Cited By ~ 3

Author(s):

Udo Frieß ◽

Steffen Beirle ◽

Leonardo Alvarado Bonilla ◽

Tim Bösch ◽

Martina M. Friedrich ◽

...

Keyword(s):

Radiative Transfer ◽

Trace Gases ◽

Estimation Method ◽

Synthetic Data ◽

Optimal Estimation ◽

Trace Gas ◽

Optical Absorption Spectroscopy ◽

Vertical Profiles ◽

Retrieval Algorithms ◽

Transfer Modelling

Abstract. Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) is a widely used measurement technique for the detection of a variety of atmospheric trace gases. Using inverse modelling, the observation of trace gas column densities along different lines of sight enables the retrieval of aerosol and trace gas vertical profiles in the atmospheric boundary layer using appropriate retrieval algorithms. In this study, the ability of eight profile retrieval algorithms to reconstruct vertical profiles is assessed on the basis of synthetic measurements. Five of the algorithms are based on the optimal estimation method, two on parametrised approaches, and one using an analytical approach without involving any radiative transfer modelling. The synthetic measurements consist of the median of simulated slant column densities of O4 at 360 nm and 477 nm, as well as of HCHO at 343 nm and NO2 at 477 nm, from seven datasets simulated by five different radiative transfer models. Simulations are performed for a combination of 10 trace gas and 11 aerosol profiles, as well as 11 elevation angles, 3 solar 10 zenith and 3 relative azimuth angles. Overall, the results from the different algorithms show moderate to good performance for the retrieval of vertical profiles, surface concentrations and total columns. Except for some outliers, the root mean squares difference between true and retrieved state ranges between (0:05–0:1) km1 for aerosol extinction, and (2:5–5:0) × 1010 molec/cm3 for HCHO and NO2 concentrations.

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Intercomparison of MAX-DOAS vertical profile retrieval algorithms: studies using synthetic data

Atmospheric Measurement Techniques ◽

10.5194/amt-12-2155-2019 ◽

2019 ◽

Vol 12 (4) ◽

pp. 2155-2181 ◽

Cited By ~ 9

Author(s):

Udo Frieß ◽

Steffen Beirle ◽

Leonardo Alvarado Bonilla ◽

Tim Bösch ◽

Martina M. Friedrich ◽

...

Keyword(s):

Radiative Transfer ◽

Trace Gases ◽

Estimation Method ◽

Synthetic Data ◽

Optimal Estimation ◽

Trace Gas ◽

Optical Absorption Spectroscopy ◽

Vertical Profiles ◽

Retrieval Algorithms ◽

Mean Square Difference

Abstract. Multi-axis differential optical absorption spectroscopy (MAX-DOAS) is a widely used measurement technique for the detection of a variety of atmospheric trace gases. Using inverse modelling, the observation of trace gas column densities along different lines of sight enables the retrieval of aerosol and trace gas vertical profiles in the atmospheric boundary layer using appropriate retrieval algorithms. In this study, the ability of eight profile retrieval algorithms to reconstruct vertical profiles is assessed on the basis of synthetic measurements. Five of the algorithms are based on the optimal estimation method, two on parametrised approaches, and one using an analytical approach without involving any radiative transfer modelling. The synthetic measurements consist of the median of simulated slant column densities of O4 at 360 and 477 nm, as well as of HCHO at 343 nm and NO2 at 477 nm, from seven datasets simulated by five different radiative transfer models. Simulations are performed for a combination of 10 trace gas and 11 aerosol profiles, as well as 11 elevation angles, three solar zenith, and three relative azimuth angles. Overall, the results from the different algorithms show moderate to good performance for the retrieval of vertical profiles, surface concentrations, and total columns. Except for some outliers, the root-mean-square difference between the true and retrieved state ranges between (0.05–0.1) km−1 for aerosol extinction and (2.5–5.0) ×1010 molec cm−3 for HCHO and NO2 concentrations.

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The Mainz Profile Algorithm (MAPA)

10.5194/amt-2018-375 ◽

2018 ◽

Author(s):

Steffen Beirle ◽

Steffen Dörner ◽

Sebastian Donner ◽

Julia Remmers ◽

Yang Wang ◽

...

Keyword(s):

A Priori ◽

Scaling Factor ◽

Trace Gas ◽

Aerosol Extinction ◽

Vertical Profiles ◽

Mixing Ratios ◽

Surface Mixing ◽

Sensitivity Studies ◽

The Impact ◽

Good Agreement

Abstract. The Mainz profile algorithm MAPA derives vertical profiles of aerosol extinction and trace gas concentrations from MAX-DOAS measurements of slant column densities under multiple elevation angles. This manuscript presents (a) a detailed description of the MAPA algorithm v0.98, including the flagging scheme for the identification of questionable or dubious results, (b) results for the CINDI-2 campaign, and (c) sensitivity studies on the impact of a-priori assumptions such as flag thresholds. MAPA is based on a profile parameterization combining box profiles, which also might be lifted, and exponential profiles. The profile parameters yielding best match to the MAX-DOAS observations are derived by a Monte Carlo approach, making MAPA much faster than previous parameter-based inversion schemes, and directly providing distributions of profile parameters. The AODs derived with MAPA for the CINDI-2 campaign show good agreement to AERONET if a scaling factor of 0.8 is applied for O4, and the respective NO2 and HCHO surface mixing ratios match those derived from coincident long-path DOAS measurements. MAPA results are robust to modifications of the a-priori MAPA settings within plausible limits.

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Analysis of a Regional Scale Chemical-Transport Model to Investigate the Potential Capability of Satellites for Identifying a Widespread Air Pollution Event

10.20944/preprints201708.0020.v3 ◽

2017 ◽

Author(s):

Jason Welsh ◽

Jack Fishman

Keyword(s):

Transport Model ◽

Regional Scale ◽

Correlation Coefficients ◽

Ozone Production ◽

Metropolitan Region ◽

Trace Gas ◽

Chemical Transport Model ◽

Satellite Measurements ◽

Pollution Event ◽

Good Agreement

We use a regional scale photochemical transport model to investigate the surface concentrations and column integrated amounts of ozone (O3) and nitrogen dioxide (NO2) during a pollution event that occurred in the St. Louis metropolitan region in 2012. These trace gases will be two of the primary constituents that will be measured by TEMPO (Tropospheric Emissions: Monitoring of Pollution), an instrument on a geostationary platform, which will result in a dataset that has hourly temporal resolution during the daytime and ~4 km spatial resolution. Although air quality managers are most concerned with surface concentrations, satellite measurements provide a quantity that reflects a column amount, which may or may not be directly relatable to what is measured at the surface. Our model results provide reasonably good agreement with observed surface O3 concentrations (correlation coefficients ranging from 0.69 to 0.87 at each of the nine monitoring stations in the St. Louis region), which is the only trace gas dataset that can be used for verification. The model shows that a plume of O3 extends downwind from St. Louis and contains an integrated amount of ozone of ~ 16 Dobson Units (DU; 1 DU = 2.69 x 1016 molecules cm-2), an amount lower than what was observed during two massive pollution episodes in the 1980s. Based on the smaller isolatable emissions coming from St. Louis, this quantity is not unreasonable, but may also reflect the reduction of photochemical ozone production due to the implementation of emission controls that have gone into effect since the 1980s.

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Intercomparison of MAX-DOAS vertical profile retrieval algorithms: studies on field data from the CINDI-2 campaign

10.5194/amt-2019-456 ◽

2020 ◽

Cited By ~ 8

Author(s):

Jan-Lukas Tirpitz ◽

Udo Frieß ◽

François Hendrick ◽

Carlos Alberti ◽

Marc Allaart ◽

...

Keyword(s):

Lower Troposphere ◽

Trace Gas ◽

Optical Absorption Spectroscopy ◽

Measuring Instruments ◽

Visible Radiation ◽

Radiation Spectra ◽

Tropospheric Aerosol ◽

Wide Range ◽

Sun Photometer ◽

Low Sensitivity

Abstract. Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) is a well-established ground-based measurement technique for the detection of aerosols and trace gases particularly in the boundary layer and the lower troposphere: ultraviolet- and visible radiation spectra of skylight are analysed to obtain information on different atmospheric parameters, integrated over the light path from space to the instrument. An appropriate set of spectra recorded under different viewing geometries ("Multi-Axis") allows retrieval of tropospheric aerosol and trace gas vertical distributions by applying numerical inversion methods. The second Cabauw Intercomparison of Nitrogen Dioxide measuring Instruments (CINDI-2) took place in Cabauw (The Netherlands) in September 2016 with the aim of assessing the consistency of MAX-DOAS measurements of tropospheric species (NO2, HCHO, O3, HONO, CHOCHO and O4). This was achieved through the coordinated operation of 36 spectrometers operated by 24 groups from all over the world, together with a wide range of supporting reference observations (in situ analysers, balloon sondes, lidars, Long-Path DOAS, sun photometer and others). In the presented study, the retrieved CINDI-2 MAX-DOAS trace gas (NO2, HCHO) and aerosol vertical profiles of 15 participating groups using different inversion algorithms are compared and validated against the colocated supporting observations. The profiles were found to be in good qualitative agreement: most participants obtained the same features in the retrieved vertical trace gas and aerosol distributions, however sometimes at different altitudes and of different intensity. Under clear sky conditions, the root-mean-square differences of aerosol optical thicknesses, trace gas (NO2, HCHO) vertical columns and surface concentrations among the results of individual participants vary between 0.01–0.1, (1.5–15) x 1014 molec cm-2 and (0.3–8) x 1010 molec cm-3, respectively. For the comparison against supporting observations, these values increase to 0.02–0.2, (11–55) x 1014 molec cm-2 and (0.8–9) x 1010 molec cm-3. It is likely that a large part of this increase is caused by imperfect spatio-temporal overlap of the different observations. In contrast to what is often assumed, the MAX-DOAS vertically integrated extinction profiles and the sun photometer total aerosol optical thickness were found to not necessarily being comparable quantities, unless information on the real aerosol vertical distribution is available to account for the low sensitivity of MAX-DOAS observations at higher altitudes.

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Determination of an effective trace gas mixing height by differential optical absorption spectroscopy (DOAS)

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-2-1663-2009 ◽

2009 ◽

Vol 2 (4) ◽

pp. 1663-1692 ◽

Cited By ~ 1

Author(s):

B. Zhou ◽

S. N. Yang ◽

S. S. Wang ◽

T. Wagner

Keyword(s):

Trace Gases ◽

Mixing Layer ◽

Correlation Coefficients ◽

Trace Gas ◽

Optical Absorption Spectroscopy ◽

Gas Mixing ◽

Mixing Height ◽

Free Atmosphere ◽

Layer Height

Abstract. A new method for the determination of the Mixing layer Height (MH) by the DOAS technique is proposed in this article. The MH can be retrieved by a combination of active DOAS and passive DOAS observations of atmospheric trace gases; here we focus on observations of NO2. Because our observations are sensitive to the vertical distribution of trace gases, we refer to the retrieved layer height as an ''effective trace gas mixing height'' (ETMH). By analyzing trace gas observations in Shanghai over one year (1017 hourly means in 93 days in 2007), the retrieved ETMH was found to range between 0.1 km and 2.8 km (average is 0.78 km); more than 90% of the measurements yield an ETMH between 0.2 km and 2.0 km. The seasonal and diurnal variation of the ETMH shows good agreement with mixing layer heights derived from meteorological observations. We investigated the relationship of the derived ETMH to temperature and wind speed and found correlation coefficients of 0.65 and 0.37, respectively. Also the wind direction has an impact on the measurement to some extent. Especially in cases when the air flow comes from highly polluted areas and the atmospheric lifetime of NO2 is long (e.g. in winter), the NO2 concentration at high altitudes over the measurement site can be enhanced, which leads to an overestimation of the ETMH. Enhanced NO2 concentrations in the free atmosphere and heterogeneity within the mixing layer can cause additional uncertainties. Our method could be easily extended to other species like e.g. SO2, HCHO or Glyoxal. Simultaneous studies of these molecules could yield valuable information on their respective atmospheric lifetimes.

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Reactive bromine in the low troposphere of Antarctica: estimations at two research sites

Atmospheric Chemistry and Physics ◽

10.5194/acp-18-8549-2018 ◽

2018 ◽

Vol 18 (12) ◽

pp. 8549-8570 ◽

Cited By ~ 4

Author(s):

Cristina Prados-Roman ◽

Laura Gómez-Martín ◽

Olga Puentedura ◽

Mónica Navarro-Comas ◽

Javier Iglesias ◽

...

Keyword(s):

Arctic Region ◽

The Arctic ◽

Trace Gas ◽

Optical Absorption Spectroscopy ◽

Ancillary Data ◽

Reactive Halogen Species ◽

The Subject ◽

The Antarctic ◽

Halogen Species ◽

The Arctic Region

Abstract. For decades, reactive halogen species (RHSs) have been the subject of detailed scientific research due to their influence on the oxidizing capacity of the atmosphere and on the climate. From the RHSs, those containing bromine are of particular interest in the polar troposphere as a result of their link to ozone-depletion events (ODEs) and to the perturbation of the cycle of toxic mercury, for example. Given its remoteness and related limited accessibility compared to the Arctic region, the RHSs in the Antarctic troposphere are still poorly characterized. This work presents ground-based observations of tropospheric BrO from two different Antarctic locations: Marambio Base (64∘13′ S, 56∘37′ W) and Belgrano II Base (77∘52′ S, 34∘7′ W) during the sunlit period of 2015. By means of MAX-DOAS (Multi-axis Differential Optical Absorption Spectroscopy) measurements of BrO performed from the two research sites, the seasonal variation in this reactive trace gas is described along with its vertical and geographical distribution in the Antarctic environment. Results show an overall vertical profile of BrO mixing ratio decreasing with altitude, with a median value of 1.6 pmol mol−1 in the lowest layers of the troposphere. Additionally, observations show that the polar sunrise triggers a geographical heterogeneous increase in bromine content in the Antarctic troposphere yielding a maximum BrO at Marambio (26 pmol mol−1), amounting to 3-fold the values observed at Belgrano at dawn. Data presented herein are combined with previous studies and ancillary data to update and expand our knowledge of the geographical and vertical distribution of BrO in the Antarctic troposphere, revealing Marambio as one of the locations with the highest BrO reported so far in Antarctica. Furthermore, the observations gathered during 2015 serve as a proxy to investigate the budget of reactive bromine (BrOx = Br + BrO) and the bromine-mediated ozone loss rate in the Antarctic troposphere.

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Polar Stratospheric Clouds Detection at Belgrano II Antarctic Station with Visible Ground-Based Spectroscopic Measurements

Remote Sensing ◽

10.3390/rs13081412 ◽

2021 ◽

Vol 13 (8) ◽

pp. 1412

Author(s):

Laura Gomez-Martin ◽

Daniel Toledo ◽

Cristina Prados-Roman ◽

Jose Antonio Adame ◽

Hector Ochoa ◽

...

Keyword(s):

Trace Gas ◽

Optical Absorption Spectroscopy ◽

Polar Stratospheric Clouds ◽

Meteorological Model ◽

Weather Forecasts ◽

Stratospheric Temperature ◽

Medium Range ◽

Stratospheric Clouds ◽

Good Agreement

By studying the evolution of the color index (CI) during twilight at high latitudes, polar stratospheric clouds (PSCs) can be detected and characterized. In this work, this method has been applied to the measurements obtained by a visible ground-based spectrometer and PSCs have been studied over the Belgrano II Antarctic station for years 2018 and 2019. The methodology applied has been validated by full spherical radiative transfer simulations, which confirm that PSCs can be detected and their altitude estimated with this instrumentation. Moreover, our investigation shows that this method is useful even in presence of optically thin tropospheric clouds or aerosols. PSCs observed in this work have been classified by altitude. Our results are in good agreement with the stratospheric temperature evolution obtained by the global meteorological model ECMWF (European Centre for Medium Range Weather Forecasts) and with satellite PSCs observations from CALIPSO (Cloud-Aerosol-Lidar and Infrared Pathfinder Satellite Observations). To investigate the presence and long-term evolution of PSCs, the methodology used in this work could also be applied to foreseen and/or historical observations obtained with ground-based spectrometers such e. g. those dedicated to Differential Optical Absorption Spectroscopy (DOAS) for trace gas observation in Arctic and Antarctic sites.

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The vertical distribution of aerosols, Saharan dust and cirrus clouds at Rome (Italy) in the year 2001

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-3-5755-2003 ◽

2003 ◽

Vol 3 (6) ◽

pp. 5755-5775 ◽

Cited By ~ 4

Author(s):

G. P. Gobbi ◽

F. Barnaba

Keyword(s):

Boundary Layer ◽

Cirrus Clouds ◽

Saharan Dust ◽

Vertical Profiles ◽

Tropospheric Aerosol ◽

Yearly Average ◽

Seasonal Analysis ◽

The Vertical Distribution ◽

532 Nm ◽

Good Agreement

Abstract. A set of 813 lidar profiles of tropospheric aerosol and cirrus clouds extinction and depolarization observed at Rome, Italy, between February 2001 and February 2002 is analyzed and discussed. The yearly record reveals a meaningful contribution of both cirrus clouds (38%) and Saharan dust (12%) to the total optical thickness (OT) of 0.26, at 532 nm. Seasonal analysis shows the planetary boundary layer (PBL) aerosols to be confined below 2 km in winter and 3.8 km in summer, with relevant OT shifting from 0.08 to 0.16, respectively. Cirrus clouds maximize in spring and autumn, in both cases with average OT similar to the PBL aerosols one. With the exception of winter months, Saharan dust is found to represent an important third layer mostly residing between PBL aerosols and cirrus clouds, with yearly average OT~0.03. Saharan dust and cirrus clouds were detected in 20% and in 45% of the observational days, respectively. Validation of the lidar OT retrievals against collocated sunphotometer observations show very good agreement. These results represent one of the few yearly records of tropospheric aerosol vertical profiles available in the literature.

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