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

2020 ◽  
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.

The information content of skylight polarisation in MAX-DOAS trace gas and aerosol profiling applications

2020 ◽  
Author(s):  
Jan-Lukas Tirpitz ◽  
Udo Frieß ◽  
Ulrich Platt
Keyword(s):  
Information Content ◽  
Atmospheric Aerosol ◽  
Ultra Violet ◽  
Single Step ◽  
Trace Gas ◽  
Optical Absorption Spectroscopy ◽  
Limited Information ◽  
Inversion Algorithm ◽  
Visible Radiation ◽  
Radiation Spectra

<p>Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) is a well-established ground-based measurement technique for the detection of atmospheric aerosol and trace gases: ultra-violet and visible radiation spectra of skylight are analyzed to obtain information on different atmospheric parameters. An appropriate set of spectra recorded under different viewing geometries ("Multi-Axis") allows retrieval of aerosol and trace gas vertical distributions by applying numerical inversion methods. Currently one of the method’s major limitations is the limited information content in the measurements that reduces the sensitivity particularly at higher altitudes.</p><p>It is well known but not yet used in MAX-DOAS profile retrievals that measuring skylight of different polarisation directions provides additional information: the degree of polarisation for instance strongly depends on the atmospheric aerosol content and the aerosol properties and – since the light path (?) differs for light of different polarisation -  the set of geometries available for the inversion is extended. We present a novel polarization-sensitive MAX-DOAS instrument and a corresponding inversion algorithm, capable of using polarization information. Further, in contrast to existing MAX-DOAS algorithms consisting of separate aerosol and trace gas retrieval modules, our novel inversion scheme simultaneously retrieves aerosol and trace gas profiles of several species in a single step. The improvement over “unpolarised” MAX-DOAS approaches will be discussed, based on both, synthetic data and real measurements.</p>

The information content of skylight polarisation in MAX-DOAS trace gas- and aerosol profiling applications 

2021 ◽  
Author(s):  
Jan-Lukas Tirpitz ◽  
Udo Frieß ◽  
Ulrich Platt
Keyword(s):  
Information Content ◽  
Atmospheric Aerosol ◽  
Ultra Violet ◽  
Trace Gas ◽  
Optical Absorption Spectroscopy ◽  
Limited Information ◽  
Inversion Algorithm ◽  
Visible Radiation ◽  
Radiation Spectra ◽  
Aerosol Properties

<p>Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) is a well-established measurement technique for the detection of atmospheric aerosol and trace gases: ultra-violet and visible radiation spectra of skylight are analyzed to obtain information on different atmospheric parameters. An appropriate set of spectra recorded under different viewing geometries ("Multi-Axis") allows retrieval of aerosol and trace gas vertical distributions as well as aerosol properties by applying numerical inversion methods. Currently one of the method’s major limitations in ground-based applications is the limited information contained in the measurements that reduces the sensitivity, particularly at higher altitudes.</p><p>It is well known but not yet used in MAX-DOAS profile retrievals that measuring skylight of different polarisation directions provides additional information: The degree of polarisation for instance strongly depends on the atmospheric aerosol content and the aerosol properties and – since the light path differs for the light of different polarisation -  the set of geometries available for the inversion is extended. We present a novel polarization-sensitive MAX-DOAS instrument (PMAX-DOAS) and a corresponding inversion algorithm, capable of using polarimetric information to significantly extend the information content of the measurements. The improvement over conventional “unpolarised” MAX-DOAS approaches will be discussed, based on both, synthetic data and real measurements.</p>

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

2021 ◽  
Vol 14 (1) ◽  
pp. 1-35
Author(s):  
Jan-Lukas Tirpitz ◽  
Udo Frieß ◽  
François Hendrick ◽  
Carlos Alberti ◽  
Marc Allaart ◽  
...  
Keyword(s):  
Optical Properties ◽  
A Priori ◽  
Optimal Estimation ◽  
Trace Gas ◽  
Optical Absorption Spectroscopy ◽  
The Sun ◽  
Aerosol Optical Properties ◽  
Estimation Algorithms ◽  
Wide Range ◽  
Sun Photometer

Abstract. 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 multi-axis differential optical absorption spectroscopy (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, direct-sun DOAS, Sun photometer and meteorological instruments). 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, with the focus on aerosol optical thicknesses (AOTs), trace gas vertical column densities (VCDs) and trace gas surface concentrations. The algorithms are based on three different techniques: six use the optimal estimation method, two use a parameterized approach and one algorithm relies on simplified radiative transport assumptions and analytical calculations. To assess the agreement among the inversion algorithms independent of inconsistencies in the trace gas slant column density acquisition, participants applied their inversion to a common set of slant columns. Further, important settings like the retrieval grid, profiles of O3, temperature and pressure as well as aerosol optical properties and a priori assumptions (for optimal estimation algorithms) have been prescribed to reduce possible sources of discrepancies. The profiling results were found to be in good qualitative agreement: most participants obtained the same features in the retrieved vertical trace gas and aerosol distributions; however, these are sometimes at different altitudes and of different magnitudes. Under clear-sky conditions, the root-mean-square differences (RMSDs) among the results of individual participants are in the range of 0.01–0.1 for AOTs, (1.5–15) ×1014molec.cm-2 for trace gas (NO2, HCHO) VCDs and (0.3–8)×1010molec.cm-3 for trace gas surface concentrations. These values compare to approximate average optical thicknesses of 0.3, trace gas vertical columns of 90×1014molec.cm-2 and trace gas surface concentrations of 11×1010molec.cm-3 observed over the campaign period. The discrepancies originate from differences in the applied techniques, the exact implementation of the algorithms and the user-defined settings that were not prescribed. For the comparison against supporting observations, the RMSDs increase to a range of 0.02–0.2 against AOTs from the Sun photometer, (11–55)×1014molec.cm-2 against trace gas VCDs from direct-sun DOAS observations and (0.8–9)×1010molec.cm-3 against surface concentrations from the long-path DOAS instrument. This increase in RMSDs is most likely caused by uncertainties in the supporting data, spatiotemporal mismatch among the observations and simplified assumptions particularly on aerosol optical properties made for the MAX-DOAS retrieval. As a side investigation, the comparison was repeated with the participants retrieving profiles from their own differential slant column densities (dSCDs) acquired during the campaign. In this case, the consistency among the participants degrades by about 30 % for AOTs, by 180 % (40 %) for HCHO (NO2) VCDs and by 90 % (20 %) for HCHO (NO2) surface concentrations. In former publications and also during this comparison study, it was found that MAX-DOAS vertically integrated aerosol extinction coefficient profiles systematically underestimate the AOT observed by the Sun photometer. For the first time, it is quantitatively shown that for optimal estimation algorithms this can be largely explained and compensated by considering biases arising from the reduced sensitivity of MAX-DOAS observations to higher altitudes and associated a priori assumptions.

scholarly journals Enhancing MAX-DOAS atmospheric state retrievals by multispectral polarimetry – studies using synthetic data

2021 ◽  
Author(s):  
Jan-Lukas Tirpitz ◽  
Udo Frieß ◽  
Robert Spurr ◽  
Ulrich Platt
Keyword(s):  
Atmospheric Aerosol ◽  
Trace Gases ◽  
Trace Gas ◽  
Optical Absorption Spectroscopy ◽  
Transfer Model ◽  
Atmospheric Parameters ◽  
Visible Radiation ◽  
Radiation Spectra ◽  
Vertical Distributions ◽  
Aerosol Properties

Abstract. Ground-based Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) is a widely-used measurement technique for the remote detection of atmospheric aerosol and trace gases. The technique relies on the analysis ultra-violet and visible radiation spectra of scattered sunlight (skylight) to obtain information on different atmospheric parameters. From an appropriate set of spectra recorded under different viewing directions (typically a group of observations at different elevation angles) the retrieval of aerosol and trace gas vertical distributions is achieved through numerical inversion methods. It is well known that the polarisation state of skylight is particularly sensitive to atmospheric aerosol content as well as aerosol properties, and that polarimetric measurement could therefore provide additional information for MAX-DOAS profile retrievals; however such measurement have not yet been used for this purpose. To address this issue, we have developed the RAPSODI (Retrieval of Atmospheric Parameters from Spectroscopic Observations using DOAS Instruments) algorithm. In contrast to existing MAX-DOAS algorithms, it can process polarimetric information, and it can retrieve simultaneously profiles of aerosols and various trace gases at multiple wavelengths in a single retrieval step; a further advantage is that it contains a Mie scattering model, allowing for the retrieval aerosol microphysical properties. The forward model component in RAPSODI is based on a linearized vector radiative transfer model with Jacobian facilities, and we have used this model to create a data base of synthetic measurements in order to carry out sensitivity analyses aimed at assessing the potential of polarimetric MAX-DOAS observations. We find that multispectral polarimetry significantly enhances the sensitivity, particularly to aerosol related quantities. Assuming typical viewing geometries, the degree of freedom for signal (DFS) increases by about 50 % and 70 % for aerosol vertical distributions and aerosol properties, respectively, and by approximately 10 % for trace gas vertical profiles. For an idealised scenario with a horizontally homogeneous atmosphere, our findings predict an improvement in the inversions results' accuracy (root-mean-square deviations to the true values) of about 60 % for aerosol VCDs as well as for aerosol surface concentrations, and by 40 % for aerosol properties. For trace gas VCDs, very little improvement is apparent, although the accuracy of trace gas surface concentrations improves by about 50 %.

scholarly journals Parameterization retrieval of trace gas volume mixing ratios from airborne MAX-DOAS

2016 ◽  
Author(s):  
Barbara Dix ◽  
Theodore K. Koenig ◽  
Rainer Volkamer
Keyword(s):  
Column Density ◽  
Elevation Angle ◽  
Trace Gas ◽  
Optical Absorption Spectroscopy ◽  
Aerosol Extinction ◽  
Reference Spectrum ◽  
Atmospheric Conditions ◽  
Tropical Ocean ◽  
Mixing Ratios ◽  
Wide Range

Abstract. We present a parameterization retrieval of volume mixing ratios (VMR) from differential slant column density (dSCD) measurements by airborne multi-axis differential optical absorption spectroscopy (AMAX-DOAS). The method makes use of the fact that horizontally recorded limb spectra (elevation angle 0°) are strongly sensitive to the atmospheric layer at instrument altitude. These limb spectra are analysed using reference spectra that largely cancel out column contributions from above and below the instrument, so that the resulting limb dSCDs, i.e., the column integrated concentration with respect to a reference spectrum, are almost exclusively sensitive to the atmospheric layers around instrument altitude. The conversion of limb dSCDs into VMRs is then realized by calculating box-air mass factors (Box-AMFs) for a Rayleigh atmosphere and applying a scaling factor constrained by O4 dSCDs to account for aerosol extinction. An iterative VMR retrieval scheme corrects for trace gas profile shape effects. Benefits of this method are 1) a fast conversion that only requires the computation of Box-AMFs in a Rayleigh atmosphere; 2) neither local aerosol extinction nor the slant column density in the DOAS reference (SCDref) need to be known; and 3) VMRs can be retrieved for every measurement point along a flight track, in contrast to profile inversion techniques. Sensitivity studies are performed for bromine monoxide (BrO), iodine monoxide (IO) and nitrogen dioxide (NO2), using 1) simulated dSCD data for different trace gas and aerosol profiles; and 2) field measurements from the Tropical Ocean tRoposphere Exchange of Reactive halogen species and Oxygenated VOC (TORERO) field experiment. For simulated data in a Rayleigh atmosphere, the agreement between the VMR from the parameterization method (VMRpara) and the true VMR (VMRtrue) is excellent for all trace gases. Offsets, slopes and R2 values for the linear fit of VMRpara over VMRtrue are as follows: BrO: (0.008 ± 0.001) pptv, 0.988 ± 0.001, 0.987; IO: (−0.0066 ± 0.0001) pptv, 1.0021 ± 0.0003, 0.9979; NO2: (−0.17 ± 0.03) pptv, 1.0036 ± 0.0001, 0.9997. The agreement for atmospheres with aerosol shows comparable R2 values to the Rayleigh case, but slopes deviate a bit more from one: BrO: (0.093 ± 0.002) pptv, 0.933 ± 0.002, 0.907; IO: (0.0021 ± 0.0004) pptv, 0.887 ± 0.001, 0.973; NO2: (8.5 ± 0.1) pptv, 0.8302 ± 0.0006, 0.9923. VMRpara from field data are further compared with optimal estimation retrievals (VMROE). Least orthogonal distance fit of the data give the following equations: BrOpara = (0.1 ± 0.2) pptv + (0.95 ± 0.14) x BrOOE; IOpara = (0.01 ± 0.02) pptv + (1.00 ± 0.12) x IOOE; NO2para = (1.7 ± 8.0) pptv + (0.90 ± 0.51) x NO2OE. Overall, we conclude that the parameterization retrieval is accurate with an uncertainty of 20 % for IO, 30 % for BrO and NO2, but not better than 0.05 pptv IO, 0.5 pptv BrO, and 10 pptv NO2. The retrieval is applicable over a wide range of atmospheric conditions and measurement geometries, and not limited to the interpretation of vertical profile measurements in the remote troposphere.

Tropospheric trace gas slant column densities derived from MAX-DOAS measurements on pacific transit cruises of the German research vessel Sonne in 2019

2020 ◽  
Author(s):  
Steffen Dörner ◽  
Thomas Ruhtz ◽  
Sebastian Donner ◽  
Steffen Beirle ◽  
Stefan Kinne ◽  
...  
Keyword(s):  
Trace Gas ◽  
Research Vessel ◽  
Optical Absorption Spectroscopy ◽  
Satellite Measurements ◽  
Climatic Zones ◽  
Bromine Oxide ◽  
The Pacific ◽  
Wide Range ◽  
German Research ◽  
Halogen Species

<p>Between January and July 2019 the German research vessel Sonne was on several cruises in the Pacific, crossing the ocean from Suva, Fiji to Manzanillo, Mexico in February (SO267-2) and from Vancouver, Canada to Singapore in June (SO268-3). A Multi Axis-Differential Optical Absorption Spectroscopy (MAX-DOAS) instrument was in operation outside the national exclusive economic zone (EEZ) regions allowing for profile measurements of trace gases and aerosol on the open seas under background conditions. Both transit cruises cover a wide range of marine biomes and climatic zones affecting the trace gas and particle composition of the atmosphere.</p><p>Ship measurements of Nitrogen Dioxide (NO<sub>2</sub>) and Sulphur Dioxide (SO<sub>2</sub>) are especially important for the validation of satellite measurements as the remote Pacific Ocean is typically used as a reference region. Off the coast of North America an enhanced signal of halogen species, i.e. bromine oxide (BrO) and iodine oxide (IO) was observed. The abundance of formaldehyde (HCHO) and its interrelation with the marine bio-activity could also be observed.</p>

scholarly journals Parameterization retrieval of trace gas volume mixing ratios from Airborne MAX-DOAS

2016 ◽  
Vol 9 (11) ◽  
pp. 5655-5675 ◽  
Author(s):  
Barbara Dix ◽  
Theodore K. Koenig ◽  
Rainer Volkamer
Keyword(s):  
Column Density ◽  
Elevation Angle ◽  
Trace Gas ◽  
Optical Absorption Spectroscopy ◽  
Aerosol Extinction ◽  
Reference Spectrum ◽  
Atmospheric Conditions ◽  
Tropical Ocean ◽  
Mixing Ratios ◽  
Wide Range

Abstract. We present a parameterization retrieval of volume mixing ratios (VMRs) from differential slant column density (dSCD) measurements by Airborne Multi-AXis Differential Optical Absorption Spectroscopy (AMAX-DOAS). The method makes use of the fact that horizontally recorded limb spectra (elevation angle 0°) are strongly sensitive to the atmospheric layer at instrument altitude. These limb spectra are analyzed using reference spectra that largely cancel out column contributions from above and below the instrument, so that the resulting limb dSCDs, i.e., the column integrated concentration with respect to a reference spectrum, are almost exclusively sensitive to the atmospheric layers around instrument altitude. The conversion of limb dSCDs into VMRs is then realized by calculating box air mass factors (Box-AMFs) for a Rayleigh atmosphere and applying a scaling factor constrained by O4 dSCDs to account for aerosol extinction. An iterative VMR retrieval scheme corrects for trace gas profile shape effects. Benefits of this method are (1) a fast conversion that only requires the computation of Box-AMFs in a Rayleigh atmosphere; (2) neither local aerosol extinction nor the slant column density in the DOAS reference (SCDref) needs to be known; and (3) VMRs can be retrieved for every measurement point along a flight track, thus increasing statistics and adding flexibility to capture concentration gradients. Sensitivity studies are performed for bromine monoxide (BrO), iodine monoxide (IO) and nitrogen dioxide (NO2), using (1) simulated dSCD data for different trace gas and aerosol profiles and (2) field measurements from the Tropical Ocean tRoposphere Exchange of Reactive halogen species and Oxygenated VOC (TORERO) field experiment. For simulated data in a Rayleigh atmosphere, the agreement between the VMR from the parameterization method (VMRpara) and the true VMR (VMRtrue) is excellent for all trace gases. Offsets, slopes and R2 values for the linear fit of VMRpara over VMRtrue are, respectively (0.008 ± 0.001) pptv, 0.988 ± 0.001, 0.987 for BrO; (−0.0066 ± 0.0001) pptv, 1.0021 ± 0.0003, 0.9979 for IO; (−0.17 ± 0.03) pptv, 1.0036 ± 0.0001, 0.9997 for NO2. The agreement for atmospheres with aerosol shows comparable R2 values to the Rayleigh case, but slopes deviate a bit more from one: (0.093 ± 0.002) pptv, 0.933 ± 0.002, 0.907 for BrO; (0.0021 ± 0.0004) pptv, 0.887 ± 0.001, 0.973 for IO; (8.5 ± 0.1) pptv, 0.8302 ± 0.0006, 0.9923 for NO2. VMRpara from field data are further compared with optimal estimation retrievals (VMROE). Least orthogonal distance fit of the data give the following equations: BrOpara =  (0.1 ± 0.2) pptv + (0.95 ± 0.14)  ×  BrOOE; IOpara =  (0.01 ± 0.02) pptv + (1.00 ± 0.12)  ×  IOOE; NO2para  =  (3.9 ± 2.5) pptv + (0.87 ± 0.15)  ×  NO2OE. Overall, we conclude that the parameterization retrieval is accurate with an uncertainty of 20 % for IO, 30 % for BrO and NO2, but not better than 0.05 pptv IO, 0.5 pptv BrO and 10 pptv NO2. The retrieval is applicable over a wide range of atmospheric conditions and measurement geometries and not limited to the interpretation of vertical profile measurements in the remote troposphere.

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

2021 ◽  
Author(s):  
Dimitris Karagkiozidis ◽  
Martina Michaela Friedrich ◽  
Steffen Beirle ◽  
Alkiviadis Bais ◽  
François Hendrick ◽  
...  
Keyword(s):  
Estimation Method ◽  
Correlation Coefficients ◽  
Scaling Factor ◽  
Trace Gas ◽  
Optical Absorption Spectroscopy ◽  
Systematic Bias ◽  
Vertical Profiles ◽  
Ancillary Data ◽  
Tropospheric Aerosol ◽  
Good Agreement

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.

scholarly journals Intercomparison of aerosol extinction profiles retrieved from MAX-DOAS measurements

2016 ◽  
Author(s):  
U. Frieß ◽  
H. Klein Baltink ◽  
S. Beirle ◽  
K. Clèmer ◽  
F. Hendrick ◽  
...  
Keyword(s):  
Optimal Estimation ◽  
Optical Absorption Spectroscopy ◽  
Measuring Instruments ◽  
Aerosol Extinction ◽  
Vertical Profiles ◽  
Near Surface ◽  
Aerosol Absorption ◽  
Sun Photometer ◽  
Absorption Measurements

Abstract. A first direct intercomparison of aerosol vertical profiles from Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) observations, performed during the Cabauw Intercomparison Campaign of Nitrogen Dioxide measuring Instruments (CINDI) in summer 2009, is presented. Five out of 14 participants of the CINDI campaign reported aerosol extinction profiles and aerosol optical thickness (AOT) as deduced from observations of differential slant column densities of the oxygen collision complex (O4) at different elevation angles. Aerosol vertical profiles and AOT are compared to backscatter profiles from a ceilometer instrument and to sun photometer measurements, respectively. Furthermore, the near-surface aerosol extinction coefficient is compared to in-situ measurements of a humidity controlled nephelometer and dry aerosol absorption measurements. The participants of this intercomparison exercise use different approaches for the retrieval of aerosol information, including the retrieval of the full vertical profile using optimal estimation and a parametrised approach with a prescribed profile shape. Despite these large conceptual differences, and also differences in the wavelength of the observed O4 absorption band, good agreement in terms of the vertical structure of aerosols within the boundary layer is achieved between the aerosol extinction profiles retrieved by the different groups and the backscatter profiles observed by the ceilometer instrument. AOT from MAX-DOAS and sun photometer show a good correlation (R > 0.8), but all participants systematically underestimate the AOT. Substantial differences between the near-surface aerosol extinction from MAX-DOAS and from the humidified nephelometer remain largely unresolved.

scholarly journals First retrieval of tropospheric aerosol profiles using MAX-DOAS and comparison with lidar and sky radiometer measurements

2008 ◽  
Vol 8 (2) ◽  
pp. 341-350 ◽  
Author(s):  
H. Irie ◽  
Y. Kanaya ◽  
H. Akimoto ◽  
H. Iwabuchi ◽  
A. Shimizu ◽  
...  
Keyword(s):  
Optical Absorption ◽  
Vertical Profile ◽  
Lower Troposphere ◽  
Optimal Estimation ◽  
Estimation Methods ◽  
Optical Absorption Spectroscopy ◽  
Lidar Data ◽  
Aerosol Extinction ◽  
Tropospheric Aerosol ◽  
Aerosol Extinction Coefficient

Abstract. Ground-based Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements were performed at Tsukuba, Japan (36.1° N, 140.1° E), in November–December 2006. By analyzing the measured spectra of scattered sunlight with DOAS and optimal estimation methods, we first retrieve the aerosol optical depth (τ) and the vertical profile of the aerosol extinction coefficient (k) at 476 nm in the lower troposphere. These retrieved quantities are characterized through comparisons with coincident lidar and sky radiometer measurements. The retrieved k values for layers of 0–1 and 1–2 km agree with lidar data to within 30% and 60%, respectively, for most cases, including partly cloudy conditions. Results similar to k at 0–1 km are obtained for the retrieved τ values, demonstrating that MAX-DOAS provides a new, unique aerosol dataset in the lower troposphere.

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