Orals: Tue, 29 Apr | Room 0.11/12
The third Cabauw Intercomparison of UV-Vis DOAS Instruments (CINDI-3) took place from May 21st to the 24th of June 2024 at the Cabauw Experimental Site for Atmospheric Research (CESAR), a semi-rural observational facility managed by the Dutch Meteorological Institute close to the cities of Rotterdam and Utrecht in the Netherlands. Its main objective was to intercompare UV-Vis MAX-DOAS instrument types targeting nitrogen dioxide, ozone, aerosols and several other reactive gases such as formaldehyde, glyoxal and BrO, with the aim to assess their performance under a range of observational conditions, and to progress towards the understanding of the measurement technique through community effort. The stationary UV-Vis observations were complemented with a range of additional measurements including ozone and aerosol lidars, NO2 and ozone sondes, long-path DOAS and in-situ instruments. Furthermore, mobile instruments were deployed around Cabauw, De Bilt and Rotterdam during selected days with favourable weather conditions using cars and bikes as well as a small research aircraft, to provide a more complete picture of the distribution of pollutants from the industrial and urbanised area around Rotterdam.
CINDI-3 was organised under the umbrella of NDACC and the European Research Infrastructure ACTRIS with additional support from ESA and NASA. In total, over 100 researchers from 16 countries participated to the field deployment. In this presentation, we provide an overview of the main on-site activities and we highlight first results of the post-campaign data evaluation with a focus on the ACTRIS/NDACC semi-blind intercomparison exercise and activities under way in various working groups addressing calibration, trace gas and aerosol vertical profiling, spectral retrieval improvements, and the joint exploitation of mobile and airborne measurements.
How to cite: Van Roozendael, M., Apituley, A., Kreher, K., Alves Gouveia, D., Cede, A., Friess, U., Friedrich, M. M., Spinei Lind, E., Merlaud, A., Piters, A., Richter, A., Tack, F., Wagner, T., and Ziegler, S.: Overview of the Third Cabauw Intercomparison of UV-Vis DOAS instruments (CINDI-3), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13109, https://doi.org/10.5194/egusphere-egu25-13109, 2025.
Glyoxal (CHOCHO) is an intermediate product of the oxidation of volatile organic compounds (VOCs) and has anthropogenic, biogenic and pyrogenic sources. It is an indicator of formation of secondary organic aerosols in the atmosphere and plays a role in the photochemical reactions of ozone in the troposphere. Additionally, at high concentrations glyoxal is harmful for humans. The lifetime of glyoxal in the atmosphere is short (a few hours) and it is removed from the atmosphere by photolysis, oxidation by OH, and deposition. Due to the different sources and short lifetime of glyoxal, its abundance in the atmosphere can vary between several parts per trillion (ppt) e.g., in remote parts of the oceans, to parts per billion (ppb) in the presence of strong sources, like biomass burning, industrial processes, fossil fuel combustion or over tropical rainforest regions.
Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) instruments are capable of measuring glyoxal, but the retrieval is difficult due to its relatively weak absorption compared to other trace gases. Therefore, further improvements of current MAX-DOAS glyoxal retrievals are needed.
Glyoxal was one of the target species during CINDI-3, the third semi-blind intercomparison campaign of UV-Vis DOAS instruments in Cabauw, The Netherlands. Based on the large scatter of the measurements among the participating instruments, it was identified as one of the more challenging trace gases to retrieve. A task group has been formed to develop a common and improved approach to retrieve glyoxal, using the data collected by several instruments and institutes during the campaign, and applying different retrieval software. In this study, we present the initial glyoxal retrievals from the campaign, and outline the development of improved retrieval settings, which we want to propose as a new standard for future glyoxal measurements.
How to cite: Krause, K., Richter, A., Bittner, S., Frieß, U., Ziegler, S., Gilke, R., Wagner, T., Donner, S., Ryan, R., Castelli, E., Achilli, A., Pettinari, P., Frins, E., Barragán, R., Pinardi, G., van Roozendael, M., Mak, H. W. L., Kwon, H.-A., Strong, K., Alwarda, R., Joshy, K., Bates, D., Lv, C., Li, A., Hu, Z., Karagkiozidis, D., Bais, A., Prados-Roman, C., Navarro-Comas, M., Puentedura Rodriguez, O., Yela Gonzalez, M., Chan, K. L., Liu, C., Tang, S., Xing, C., Ji, X., Lampel, J., and Bösch, H.: CINDI-3 glyoxal intercomparison, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16039, https://doi.org/10.5194/egusphere-egu25-16039, 2025.
Atmospheric trace gases near the Earth’s surface can have important human and environmental health impacts. In particular, the trace gas nitrogen dioxide (NO2), which is commonly emitted by traffic, biomass burning, and industrial sources, can be a major threat to human respiratory health, leading to increased rates of asthma, lung cancer, and overall mortality. In the Greater Toronto Area (GTA) and in the Detroit-Windsor Area (DWA), NO2 and other trace gases are being measured by ground-based Pandora UV-visible spectrometers that are part of the Pandonia Global Network. We present NO2 surface volume mixing ratios derived from Pandora direct sun total column measurements to monitor air quality in these two urban areas. The conversion method uses three inputs in addition to the Pandora total columns: (1) the stratospheric NO2 column from the Ozone Monitoring Instrument (OMI), (2) the free troposphere NO2 column from the GEOS-Chem chemical transport model, and (3) the ratio of NO2 surface volume mixing ratio to planetary boundary layer column from Environment and Climate Change Canada’s regional air quality forecast model, Global Environmental Multi-scale-Modelling Air quality and Chemistry (GEM-MACH). The derived estimates of surface NO2 are compared with in situ measurements, and their level of agreement is assessed for dependence on meteorological conditions, including wind speed and direction, temperature, and boundary layer height. The mean bias between the derived estimates and in situ measurements ranges from -1.0 ppbv to -2.6 ppbv. This bias has been found to vary with boundary layer height, so a method to account for this dependence has been developed to improve the results. This presentation will provide an overview of this column-to-surface conversion method, a summary of results for each site in the GTA and DWA, and an outline of plans toward using this approach to improve and validate satellite estimates of surface NO2.
How to cite: Bates, D., Alwarda, R., Strong, K., Zhao, X., Fioletov, V., Lee, S. C., and Su, Y.: Surface NO2 Derived from Pandora Column Measurements in Toronto and Detroit-Windsor, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14161, https://doi.org/10.5194/egusphere-egu25-14161, 2025.
Nitrogen dioxide is a key pollutant in the troposphere. Most of its sources are anthropogenic and linked to the burning of fossil fuels, but wildfires, lightning and soil emissions also contribute to the overall NOx (NO + NO2) loading.
Using passive remote sensing in the UV and visible spectral range, NO2 columns can be retrieved with both ground-based MAX-DOAS and satellite instruments. As a result of the multitude of sources and the short atmospheric lifetime of NOx, spatial and temporal variability of NO2 in the troposphere is large. This variability complicates the interpretation of satellite measurements, which integrate over relatively large areas, and also has to be considered in satellite validation.
The University of Bremen, in collaboration with the National Observatory of Athens (NOA), has been operating a MAX-DOAS instrument at the NOA premises on Penteli Hill in the northeast of Athens since 2012. The measurement location allows for several viewing directions over the city of Athens and towards less polluted background regions. The measurements are, therefore, ideal to investigate an inhomogeneous NO2 distribution and its impact on satellite validation.
Using the data from the MAX-DOAS instrument, the temporal and spatial variability of NO2 is evaluated, and simple parametrisations are developed and tested to characterise the degree of variability. Comparing the results from variations in time and those in azimuth direction, interesting similarities and differences are found. The derived inhomogeneity parameters can be used to classify situations where the MAX-DOAS data is particularly well suited for satellite validation and which days should be excluded from such evaluations.
How to cite: Richter, A., Krause, K., Gratsea, M., Seyler, A., Wittrock, F., Burrows, J. P., and Bösch, H.: MAX-DOAS observations of spatial variability of NO2 in Athens, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12396, https://doi.org/10.5194/egusphere-egu25-12396, 2025.
Bromine oxides (BrO) play a critical role in ozone depletion and boundary layer chemistry. During the spring-summer period of 2024 (May 1 to June 15), Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements were conducted in Hangzhou Bay Area, China, to observe the presence of BrO, aerosols, and other trace gases (NO₂, HCHO, etc.). The average BrO volume mixing ratio (VMR) during the observation period was 2.14 ppt, increasing to 4.24 ppt during pollution episodes. High concentrations of BrO were primarily observed in the boundary layer at altitudes of 1.5–2.5 km, while other trace gases are mainly concentrated between 0-1 km near the surface. BrO concentrations tended to peak during the morning hours (7:00 am–10:00 am local time), showing a clear correlation with aerosol variations, indicating significant photochemical activation. A anti-correlation was observed between BrO and ozone (O₃), revealing a bromine-mediated O₃ depletion mechanism.
Furthermore, the overall pollutant concentration in June was higher than in May, and this change is closely related to seasonal meteorological factors, particularly variations in wind direction and temperature, which are considered the main factors influencing BrO levels.
Validation conducted during the CINDI-3 campaign demonstrated the high reliability of MAX-DOAS measurements, confirming the robustness of the MAX-DOAS technique for monitoring coastal air quality. These findings enhance our understanding of BrO dynamics in coastal regions and their impact on atmospheric chemistry.
How to cite: Lv, C., Li, A., and Hu, Z.: Observations of BrO and other trace gases in typical regions of China based on MAX-DOAS network, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4556, https://doi.org/10.5194/egusphere-egu25-4556, 2025.
The Airborne and Satellite Investigation of Asian Air Quality (ASIA-AQ) campaign was conducted from February to March 2024 to investigate air quality in Asia. One of the primary scientific objectives of the ASIA-AQ campaign was satellite validation and interpretation, especially for the Geostationary Environment Monitoring Spectrometer (GEMS) products. To achieve this goal, nitrogen dioxide (NO2), formaldehyde (HCHO), aerosols, and other trace gases were measured using airborne and ground-based instruments. Here, we present trace gas and aerosol profile measurements from the ground-based Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) SkySpec instruments in South Korea during ASIA-AQ. We use the RAPSODI (Retrieval of Atmospheric Parameters from Spectroscopic Observations using DOAS Instruments) algorithm to retrieve profiles from MAX-DOAS measurements. The NO2 surface concentrations retrieved from MAX-DOAS are in good agreement with in-situ measurements, showing correlation coefficients of 0.63 (north direction) and 0.88 (south direction), but with negative biases of –48% and –15%, respectively. In comparison with airborne in-situ measurements, MAX-DOAS NO2 concentrations below 1 km are lower than those measured by in-situ instruments (NASA GSFC CANOE and NCAR NOx and O3 Chemiluminescence) onboard NASA’s DC-8 aircraft. These negative biases in comparison with surface and aircraft measurements are influenced by the heterogeneity of NO2 concentrations due to the differing locations of MAX-DOAS and in-situ instruments. Aerosol optical depths (AODs) derived from MAX-DOAS are well correlated with those from the Aerosol Robotic Network (AERONET). Using these MAX-DOAS measurements, we validate GEMS NO2 and AOD products. GEMS NO2 version 3 products reduce positive biases occurring in the version 2 products but remain lower than those from MAX-DOAS NO2 products. GEMS AOD products are in good agreement with AERONET and MAX-DOAS products.
How to cite: Kwon, H.-A., Ahn, S., Tirpitz, J.-L., Franchin, A., St Clair, J., Gupta, P., Lind, E., Kim, J., and Jeong, U.: Trace gas and aerosol profile measurements from MAX-DOAS in South Korea during ASIA-AQ, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4660, https://doi.org/10.5194/egusphere-egu25-4660, 2025.
Aerosol vertical profiles in the lowest 1-2 km of the atmosphere are not very well studied due to technology limitations (e.g. LIDARs) and air space restrictions (e.g. manned and unmanned aircrafts). This study investigates sensitivity of the radiance measurements in UV-VIS part of the spectrum to the aerosol profiles from the standard columnar almucantar and direct sun measurements combined with low elevation sky scanning (from the horizon to zenith direction).
GRASP algorithm is used to simulate scattered sky radiances and conduct aerosol profile inversions. Radiance measurements are conducted by the sun-sky radiometer at subset of standard AERONET wavelengths (340, 380, 440, 500, 675, 870). AErosol RObotic NETwork (AERONET) is a network of sun-sky-moon photometers that measure solar radiation at 9 wavelength bands (centered at 340, 380, 440, 500, 675, 870, 937, 1020, 1640 nm, 2-25 nm FWHM filter transmission). The main AERONET products are columnar aerosol optical depth, Angstrom exponent (from direct sun measurements), single scattering albedo and size distribution (from Almucantar and hybrid scans). The additional products investigated in this study are volume density and aerosol extinction coefficient profiles. This study evaluates CIMEL 318T pointing accuracy (near horizon), effect of surface albedo on the inversions and ability of radiance measurements to invert vertical profiles both from synthetic and real measurements at 2 locations: Greenbelt, MD and Rotterdam, NL.
How to cite: Lind, E., Herreras-Giralda, M., Momoi, M., Eck, T., Sinyuk, A., and Dubovik, O.: Aerosol vertical profile measurements using passive radiometric measurements, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7208, https://doi.org/10.5194/egusphere-egu25-7208, 2025.
The NO2 camera is a novel instrument, developed by the Royal Belgian Institute for Space Aeronomy. It consists in an AOTF-based hyperspectral imager and DOAS-based data processing algorithms enabling to measure the differential slant column densities (dSCD) of NO2 along each pixel’s line of sight.
In the framework of IDEAS-QA4EO, a measurement campaign was organized in an urban environment at the BAQUNIN supersite in Rome, in March 2024. The NO2 camera was compared to two collocated reference NO2 remote sensing instruments: a PANDORA spectrometer from LuftBlick deployed at the BAQUNIN supersite, and a SkySpec-2D Max-DOAS spectrometer from Airyx, operated by CNR Isac. All instruments were synchronized to a common pointing schedule, measuring the dSCD at low elevation angles (-2° to +10°) and around 4 agreed azimuth angles with unobstructed view of the horizon. The PANDORA and SkySpec obtained their measurements by scanning in elevation and in azimuth, up to 10° left and right of each reference direction. To the best of our knowledge, this is the first time these two instruments have been compared in this manner. All dSCDs were computed using as fixed reference a zenith spectrum acquired by each instrument at the same specified time. Three days of synchronized data are available for comparison, with clear to partly cloudy weather conditions.
A total of 156 hyperspectral cubes were obtained by the NO2 camera during the synchronized periods. Several local enhancements were captured by the NO2 camera, showing the inhomogeneity of the Roman NO2 field. In total, about 6000 dSCD values from the NO2 camera were compared to the SkySpec, and about 700 values were compared to the PANDORA. The tolerance margins for inclusion in the comparison were set to 5 minutes for the acquisition time, and to 0.1° for the azimuth and elevation. Overlaying the retrievals from all instruments showed how the additional visual context captured by the camera may help understanding the location of NO2 emission sources. This can be seen in the example image below, as well as the good qualitative agreement between the instruments. More formally for the whole campaign, the measured dSCDs ranged from -2e16 to +22e16 molecules/cm². The disagreement between the camera and the SkySpec (resp. PANDORA) has mean -0.7e16 (resp. -0.01e16) molecules/ cm² and standard deviation 1.6e16 (resp 2.5e16) molecules/cm² for all points above the horizon.
We will present more details on the campaign setup and results.
How to cite: Gramme, P., Busschots, C., Dekemper, E., Casadio, S., Pettinari, P., Castelli, E., and Achilli, A.: Urban Pollution Monitoring with the AOTF-based NO2 Camera: Validation Campaign in Rome, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18486, https://doi.org/10.5194/egusphere-egu25-18486, 2025.
The emergence of spectral imaging concepts that are both sensitive and snapshot open up new perspectives in response to major challenges, such as air quality monitoring and greenhouse gas emissions. The imSPOC concept (Brevet n° : FR16/56162) is a static Fourier transform spectral imager. Its compactness, robustness, and lightness make it a promising concept for measuring greenhouse gases from space or assessing air quality. This concept is based on a paradigm shift, as it enables the acquisition of only portions of interferograms [1]. Consequently, it is necessary to transfer optimal estimation algorithms into the interferogram space: since spectral radiances cannot be retrieved from partial interferograms, it is necessary to directly fit measured interferograms to simulated interferograms in order to retrieve total columns from its measurements. Within the framework of the European Space Carbon Observatory project (H2020 SCARBO), it was demonstrated that the relevant geophysical information (CO2 column for one camera and CH4 column for the other) is indeed present in the identified interferogram portions [2]. In parallel, two prototypes were built, one dedicated to CO2 and the other to CH4. To improve the designs of these cameras, a co-design code allowing the propagation of instrumental errors to gas columns is essential.
In this work, we demonstrate how an approach based on the Cramer-Rao Lower Bound enabled a sensitivity increase of more than a factor of two for both the CO2 and CH4 cameras. The design of such instrumentation relies on both the selection of shape and spectral position of the filter, as well as the properties of the interferometric plate, which is an array of Fabry-Perot interferometers. We evaluated the impact of several design parameters: (i) the selection of the spectral shape and position of the filter, (ii) the selection of the maximum optical path difference, and (iii) the Fabry-Perot finesse of the interferometer, which enhances discrimination between different gas signatures. Further refinement of the design was achieved using the MEDOC retrieval model, incorporating additional parameters such as engraving depths, leading to an optimized repartition of the available optical path difference acquired by the spectral imaging sensor. Finally, the newl design for the CO2 camera was benchmarked against the earlier CO2 SCARBO design. The study found that the CO2 scale factor random error has been reduced by more than a factor of two. Furthermore, performance has become more consistent across varying incidence angles. Additionally, correlation between albedo and retrieved CO2 products has also decreased. This work received funding from the European Union’s H2020 research and innovation program under grant agreements No 769032 (SCARBO) and No 101135301 (SCARBOn).
[1] S. Gousset, L. Croizé, E. Le Coarer et al., “NanoCarb hyperspectral sensor: on performance optimization and analysis for greenhouse gas monitoring from a constellation of small satellites”, CEAS Space J., 11, pages 507–524 (2019)
[2] M. Dogniaux, C. Crevoisier, et al., “The Space CARBon Observatory (SCARBO) concept: Assessment of XCO2 and XCH 4 retrieval performance”. Atmospheric Measurement Techniques Discussions, 1-38.
How to cite: Croize, L. and Ferrec, Y.: Impact of the design of a spectral imager based on partially sampled interferograms on the retrieve products, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21657, https://doi.org/10.5194/egusphere-egu25-21657, 2025.
The third Cabauw intercomparison of DOAS-type instruments (CINDI-3) campaign took place at the CESAR measurement site near Cabauw, Netherlands in June 2024. Stationary DOAS instruments were supported by mobile platforms: cars, a bike and an airplane mapped the horizontal distribution of trace gases in the regions around Rotterdam and Cabauw. In this work, we combine the information gained from all mobile platforms to obtain the horizontal distribution of nitrogen dioxide (NO2). During the campaign additional MAX-DOAS instruments were set up along the main viewing azimuth direction to investigate the retrieval of horizontal gradients from MAX-DOAS instruments using a tomographic approach. Here, we present NO2 maps obtained from the mobile measurements, the differences between the stationary instruments and the resulting implications for the tomographic approach.
How to cite: Ziegler, S., Pukite, J., Gilke, R., Ripperger-Lukosiunaite, S., Lauster, B., Reischmann, L., Donner, S., and Wagner, T.: Examining the effect of horizontal gradients in trace gas distributions during the intercomparison campaign CINDI-3, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2495, https://doi.org/10.5194/egusphere-egu25-2495, 2025.
In recent years, a novel type of passive remote sensing instrument has been under development at the Royal Belgian Institute for Space Aeronomy (BIRA-IASB). The aim of this instrument, known as the NO2 camera, is to improve the spatio-temporal resolution of ground-based-observed NO2 slant column densities which are usually measured by azimuth and elevation scanning spectrometers. As a result, NO2 emitted in polluted environments can be better characterized.
The working principle of this so-called NO2 camera is based on an acousto-optical tunable filter (AOTF), a crystal whose lattice is modulated by a propagating acoustic wave. The elasto-optic effect taking place in the crystal allows the selection of any single wavelength from the incoming light bundle with a spectral resolution between 0.6 and 0.8 nm. Within this imaging optical setup, the AOTF records spectral images of a scene (in this case the atmosphere) in successive wavelengths. For our instrument, a crystal operating in the 435 to 455 nm band was selected. The resulting hyperspectral images are then processed using the DOAS technique.
Between May 21 and June 24, 2024, the BIRA-IASB NO2 camera participated in the Third Cabauw INtercomparison of DOAS-type Instruments (CINDI-3), providing an opportunity to benchmark its performance against state-of-the-art instruments. During the campaign, the camera operated in close synchronization with other participating DOAS-type instruments. Additionally, outside of the prescribed campaign protocol, the camera sampled the NO2 field in the direction of Rotterdam and Utrecht. We present the first results of these measurements, discuss their performance and highlight preliminary findings.
How to cite: Busschots, C., Gramme, P., Dekemper, E., Mettepenningen, G., Merlaud, A., and Van Roozendael, M.: AOTF-based NO2 camera: CINDI-3 results, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16804, https://doi.org/10.5194/egusphere-egu25-16804, 2025.
Ship emissions comprise up to 15% of global transport pollution. To regulate this pollution, Nitrogen Emission Control Area (NECA) and Sulphur Emission Control Area (SECA) zones have been introduced in the North Sea, which define a threshold for shipping emissions of respectively NOx and SOx. The current method of control of these regulations in the Belgian North Sea uses an aircraft equipped with sniffers to fly through the plume. As this is an intensive method, only a limited number of ships can be evaluated. The Ship Emission Monitoring by Passive Absorption Spectroscopy (SEMPAS) project develops a UV-Visible Differential Optical Absorption Spectroscopy (DOAS) instrument to permanently monitor ships from a Belgian offshore windfarm and to complement the aircraft-based measurements.
As part of a preparatory stage prior to its deployment on an off-shore wind farm conversion platform, the imaging DOAS system with a field of view of 0.2x3 degrees is installed in the port of Zeebrugge at the Belgian North Sea coast. From there, it measures slant columns of both SO2 and NO2 in the UV at a spectral resolution of 0.4 nm, as proxies for NOx and SOx. The aim of the project is to use these measurements to quantify shipping emission factors, to check for compliance of the emission factors as defined in NECA and SECA zones. Additionally, the instrument will be used as a MAX-DOAS system, to study the variability of atmospheric trace gases and contribute to the validation of satellite measurements in a marine environment.
To enhance sensitivity of the ship plume, an image recognition AI-based algorithm identifies ships on a camera accompanying the instrument. By accurate pointing of the system, ships can be tracked actively in their course. This enlarges the time in view of the instrument and as such increases the measurement signal. With this technique, we explore whether the sensitivity required for monitoring of the current strict regulations can be reached.
The poster addresses the installation of the instrument and finetuning of the ship-tracking algorithm. We discuss the identification of shipping emissions based on the DOAS technique and show first results.
How to cite: Mettepenningen, G., Fayt, C., Tack, F., Van Doorne, C., Jacobs, L., Berkenbosch, S., Aubry, A., Desmet, F., De Mazière, M., and Van Roozendael, M.: UV-Vis remote sensing of shipping emissions and atmospheric pollutants at the North Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7990, https://doi.org/10.5194/egusphere-egu25-7990, 2025.
In August 2023 and September 2024, King’s College London (KCL) conducted airborne campaigns in Canada to investigate emissions from wildfires and the oil industry. The British Antarctic Survey (BAS) Twin Otter aircraft was equipped with an array of in-situ and remote sensing instruments, including the SWING instrument. Developed by the Royal Belgian Institute for Space Aeronomy (BIRA-IASB), SWING is a compact whiskbroom imager designed to map trace gases that absorb in the UV-visible spectral range (300-550 nm).
We present the integration of SWING into the BAS Twin Otter and its operations during the airborne campaigns. On 14 and 19 August 2023, the aircraft sampled the plume from a wildfire in Ontario, measuring NO2. On 11 September 2024, the aircraft flew over a fire in Saskatchewan, where we detected NO2 together with HCHO and HONO. In the same 2024 campaign, we observed NO2 emissions from flaring at oil facilities in Alberta: Fort McMurray, Fort McKay, and from chemical plants near Edmonton. These airborne measurements are compared with satellite-based air quality data from TROPOMI and TEMPO, for which we are close to the northern edge of the field of view. We also estimate the HONO/NO2 from the fire and investigate how such measurements may help to quantify the emissions from wildfires and from natural gas flaring.
How to cite: Merlaud, A., Tack, F., Theys, N., Van Roozendael, M., Owlsey-Brown, F., Middleton, C., Maslanka, W., Wainwright, T., Richardson-Foulger, L., Wooster, M., and Schuettemeyer, D.: Airborne Measurements of NO2, HONO, and HCHO Emissions from Canadian Wildfires and the Oil Industry, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17520, https://doi.org/10.5194/egusphere-egu25-17520, 2025.
Carbon dioxide (CO2) is usually the second most abundant gas in volcanic plumes. Its early dissolution from rising magmas can allow insights into magmatic source regions and subsurface volcanic structures. Due to its chemical inertness, CO2 measurements are particularly valuable for studying plume chemistry using CO2 as a mixing tracer. The also relatively abundant volcanic gases, hydrogen fluoride (HF) and hydrogen chloride (HCl), dissolve at shallower depths. Their measurements, along with those of other halogen and sulfur compounds, complement the insights into the volcanic system and plume composition. Continuous measurements of volcanic CO2, HF, and HCl emissions could therefore enhance our understanding of volcanic activity and improve hazard assessment.
Remote sensing measurements of volcanic gases in the shortwave infrared (SWIR) spectral range offer the potential for automated, continuous data acquisition of the above-mentioned gases. However, current studies are limited to direct sun geometry which restricts measurement opportunities to cases where the volcanic plume is positioned between the instrument and the sun. Therefore, we investigated the feasibility of operating a portable Fourier-transform infrared (FT-IR) spectrometer in scattered sunlight geometry for CO2, HF, and HCl measurements. This approach would enable greater measurement flexibility but introduces the challenge of a significantly weaker light source in the SWIR spectral range.
We present a framework for calculating the required averaging time to achieve specific detection limits for CO2, HF, and HCl based on instrument parameters (e.g. detector specifications, field of view, beam diameter). For Bruker’s EM27/SUN instrument, modified and optimized for scattered sunlight measurements, we estimate an averaging time of several hours to detect CO2 slant column densities at levels typical for Mt. Etna (Italy). This makes the setup studied highly impractical for volcanic CO2 measurements. In contrast, the required averaging times for HF and HCl detection are of the order of 10 minutes.
These results underscore the utility of performance calculations in guiding instrument design while highlighting the challenges associated with scattered sunlight being a weak light source in the SWIR spectral range.
How to cite: Sindram, M., Schmitt, T. D., Bobrowski, N., Kleinschek, R., Löw, B., Weis, L., and Butz, A.: Feasibility of volcanic CO2, HF, and HCl remote sensing measurements using Fourier-transform infrared spectrometry in scattered sunlight geometry, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10395, https://doi.org/10.5194/egusphere-egu25-10395, 2025.
Ship emissions of particles, SO2 and NOx (the sum of NO and NO2) are a significant contribution to air pollution, in particular in coastal areas and close to busy in-land shipping routes. Therefore, national and international regulations have been put in place to limit emissions and thereby minimize the impact of shipping on air quality. However, the monitoring of ship emissions is challenging, and so far, no automated systems are operational for systematic surveillance of compliance with regulations.
Active Optical Remote Sensing is one possible approach to measuring ship emissions. Briefly, a light source is set-up on one side of a river or port, and a reflector on the other side. The light path is positioned in such a way that the emission plume of passing ships is sampled. Using spectroscopic methods, the amounts of trace gases in the plume can be determined. With Automated Identification System (AIS) data, the plumes can be assigned to individual ships. The advantage of remote sensing over in-situ observations is a reduced dependence on wind direction, increasing the rate of successful measurements. A second important advantage is the self-calibration of the method, facilitating long-term autonomous operation without the need for on-site calibration.
This method has been successfully used in the UV/Vis wavelength range to detect SO2 and NO2 at the location of Wedel, a small town at the river Elbe, 10 km downriver of the port of Hamburg, Germany. Based on these data and a plume model, emission rates of NOx and SO2 in g s-1 could be determined with an automated method (Krause et al., 2021).
While this type of measurement is useful in determining emission rates, often specific emissions relative to the amount of fuel burnt are of interest. This is particularly the case for SO2, where regulations are based on limits for the fuel sulphur content. In order to extend the method to these quantities, an additional channel measuring CO2 in the IR part of the spectrum has to be added to the instrument. The CO2 can be used as a proxy of the amount of fuel burnt, and thereby also the energy used. In addition, direct NO measurements in the IR would reduce the uncertainties of the NOx measurements.
The SEICOR project aims at developing such a system for automated long-term surveillance of emissions from ships and other, similar sources. It is based on the experience and tools from the measurements performed in Wedel. The new system will cover all parts of the measurements, from the instrument over data analysis of the emission factors to direct generation of warnings in case of high emissions. An automated reporting to the authorities, port operators and / or ship owners is planned. Here we present technical details and first results of the measurement and validation campaign which takes place in April 2025 in Wedel at the river Elbe.
The SEICOR project is funded by the Federal Ministry for economic affairs and climate action.
How to cite: Wittrock, F., Daubinet, A., Haisch, C., Krause, K., Pöhler, D., Poppe, J., Richter, A., Rieker, M., and Schmitt, S.: SEICOR - Ship Emission Inspection with Calibration-free Optical Remote sensing, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19146, https://doi.org/10.5194/egusphere-egu25-19146, 2025.
MAX-DOAS, direct sun DOAS and FTIR measurements are increasingly used as fiducial reference measurements (FRM) for the validation of HCHO satellite observations. Understanding their strengths and limitations, and assessing their consistency is therefore crucial to produce robust and consolidated validation results. So far, only a few studies have explored the complementarity between MAX-DOAS and FTIR HCHO measurements.
In the present study, we take benefit of MAX-DOAS and FTIR instruments being simultaneously operated at the Xianghe station (39.75° N, 116.96° E, approximately 55 km southeast of Beijing) to compare HCHO vertical columns (VCDs) retrieved from both instruments during one full year in a site under the influence of strong VOC emissions from biogenic and anthropogenic origins. In addition to its standard MAX-DOAS geometry, the IAP/BIRA instrument also provides regular direct sun measurements suitable for comparison with FTIR solar absorption data. The two direct sun measurements, in the UV and IR, show an excellent agreement and form a reliable HCHO VCD reference.
We investigate results obtained using MMF and MAPA MAX-DOAS algorithms and their combined use within the FRM4DOAS centralized processing facility, assessing the agreement reached with respect to the direct sun reference data and investigate the reasons for the observed differences. A good correlation (~0.96) but with a systematic under-estimation of about -20% is found for all the MAX-DOAS approaches. We explore whether this discrepancy can be understood by the known lack of sensitivity of MAX-DOAS measurements in the free-troposphere, above 4 km of altitude. Changing the MMF a-priori profiles to monthly averaged profiles coming from CAMS or TM5 models shows a reduction of the bias of 10 to 15% with respect to the direct sun reference data. By further considering the MAX-DOAS and FTIR respective vertical sensitivities through application of their averaging kernels, we reduce the remaining bias to -2% for the different MAX-DOAS datasets.
How to cite: Pinardi, G., Van Roozendael, M., Friedrich, M. M., Langerock, B., Vigouroux, C., De Smedt, I., Hendrick, F., Wang, T., Wang, P., Zhou, M., and Beirle, S.: Intercomparison of MAX-DOAS, FTIR and direct sun DOAS HCHO retrievals in Xianghe (China), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16842, https://doi.org/10.5194/egusphere-egu25-16842, 2025.
Characterizing the microphysical properties of aerosols is crucial for understanding their impacts on air quality, climate change, and human health. In this study, we present a novel approach for determining aerosol size distribution, refractive index, and single-scattering albedo using a polarization-sensitive Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) instrument. Extracting the polarimetric state of the atmosphere through polarization-sensitive solar almucantar measurements improves the accuracy and resolution of the derived aerosol parameters.
The RAPSODI retrieval algorithm employs a bimodal size distribution within the aerosol Mie model, coupled with the VLIDORT vector forward model and inversion via the optimal estimation method. Measurements conducted at the IUP Heidelberg during the second half of 2024 provided a dataset of polarization-dependent differential slant column densities (dSCD) and differential slant optical thicknesses (dSOT), which were analyzed to derive the vertical distribution of NO₂, aerosol extinction, and the microphysical properties of the aerosols. Good correlation between measured and modeled dSCDs and dSOTs is achieved, providing confidence that microphysical aerosol parameters can be retrieved reliably with our novel remote sensing method.
The results demonstrate that the polarization-sensitive MAX-DOAS technique improves the information content for characterizing spherical aerosol particles. For validation, we performed comparisons with a co-located CIMEL sun-photometer from the Aerosol Robotic Network (AERONET). This study highlights the potential of polarization-sensitive MAX-DOAS in advancing both data collection and our understanding of aerosol properties.
How to cite: Blohm, K., Frieß, U., Lind, E. S., Tirpitz, J.-L., and Platt, U.: First retrievals of aerosol microphysical properties from polarisation-sensitive MAX-DOAS measurements, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19196, https://doi.org/10.5194/egusphere-egu25-19196, 2025.
This study investigates horizontal gradients of aerosols and trace gases using a rooftop-mounted MAX-DOAS instrument located at the Max Planck Institute for Chemistry in Mainz. Horizontal inhomogeneities, especially in urban areas or near strong emission sources, can significantly affect the accuracy of MAX-DOAS profile retrievals, as these typically assume horizontally homogeneous atmospheric conditions. The experimental setup allows for measurements in two azimuthal directions (possibly extended to 4 azimuth directions), focusing on gradients between opposing directions (180° apart). By analyzing the retrieved differential slant column densities (dSCDs) at low elevation angles horizontal gradients will be identified and quantified. They are compared to the temporal variability of the dSCDs at high elevation angles, taking into account also wind speed and direction. From the MAX-DOAS observations also trace gas and aerosol profiles are retrieved. Retrievals under conditions of strong and weak gradients are contrasted to assess their influence on the atmospheric profile retrievals. As a result, we give recommendations which situations might be favorable or not favorable for MAX-DOAS profile inversions, particularly relevant in areas influenced by complex emission sources.
How to cite: Bastani, E., Ziegler, S., Gilke, R., Donner, S., Beirle, S., and Wagner, T.: Horizontal Gradients of Aerosols and Trace Gases: Insights from MAX-DOAS Measurements in Mainz, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8855, https://doi.org/10.5194/egusphere-egu25-8855, 2025.
Cloud properties play an important role in the evaluation and interpretation of Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements. Clouds strongly influence the length of atmospheric light paths, and are thus important for deriving the aerosol optical depth (AOD) and vertical column density (VCD) of trace gases from MAX-DOAS measurements. As such, information about the cloud properties is important to interpret the data.
This study focuses on comparing three methods to derive information on cloud properties which can be run in conjunction with MAX-DOAS measurements, allowing for a more comprehensive characterisation of cloud effects: a ceilometer, an infrared camera and information derived from the MAX-DOAS measurements themselves. All instruments are located at the Max-Planck Institute for Chemistry in Mainz, Germany. We investigate, under which cloud conditions MAX-DOAS inversions might yield reasonable results and under which cloud conditions inversion results have large uncertainties. One focus of our investigation is the effect of cloud altitude on the MAX-DOAS retrievals.
How to cite: Gilke, R., Reischmann, L., Ziegler, S., Bastani, E., Donner, S., Ripperger-Lukošiūnaitė, S., Kinne, S., Kumar, V., and Wagner, T.: Comparison of Cloud Classification methods, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8524, https://doi.org/10.5194/egusphere-egu25-8524, 2025.
Measuring water vapor (WV) in the troposphere, where nearly all atmospheric WV is concentrated, is critical for understanding atmospheric composition and dynamics comprehensively. A particularly challenging issue is conducting systematic WV measurements in the lower troposphere (approximately 5–6 km) on a global scale, as this would significantly enhance both climate modeling and numerical weather prediction (NWP) capabilities over short time scales.
Based on theoretical studies conducted for the European Space Agency (ESA), some of the authors proposed an innovative approach - the Normalized Differential Spectral Attenuation (NDSA) - capable of retrieving integrated water vapor (IWV) from attenuation measurements taken in the 17–21 GHz frequency band along microwave links crossing the troposphere. The NDSA technique relies on estimating a parameter, called spectral sensitivity (S), which quantifies the differential attenuation experienced by a pair of tone signals separated by a fractional bandwidth of less than 2%. It has been demonstrated that S can be directly converted into IWV using a linear relationship. Through the aforementioned ESA studies, the authors have also shown that the NDSA method can successfully estimate WV vapor from space by utilizing sets of co-rotating or counter-rotating Low Earth Orbit (LEO) satellites.
Recently, the Italian Space Agency supported the SATCROSS project, aimed at demonstrating the feasibility of a future space mission and to develop a prototype for NDSA measurements along terrestrial links operating at 19 GHz. A critical step toward consolidating progress and advancing the realization of a space-based measurement project using the NDSA approach is the performance analysis of the IWV estimates provided by prototype instruments. This includes validating those estimates by comparing them with results from other sensors and techniques, which was the objective of a four-month measurement campaign conducted from July to November 2024.
In this work, we present the main results of the campaign, conducted in a ground-to-ground configuration, designed to compare IWV measurements from the NDSA prototype instrument with those obtained using the Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) technique. MAX-DOAS retrieves IWV in the visible spectral range, specifically at about 445 nm. The independent optical device used in this study was configured to observe the same air volume as the NDSA instrument. Measurements were made along a link connecting the meteorological station "Giorgio Fea," located at the rural site of St. Pietro Capofiume, Bologna, 10 m above sea level, to the WMO/GAW (World Meteorological Organization/Global Atmosphere Watch) Climate Observatory “Ottavio Vittori” at Mount Cimone, 2165 m above sea level.
The link length is 91 km, with no physical obstacles interposed. In addition to MAX-DOAS data, measurements were also acquired and processed from radiosondes, hygrometers, GNSS (Global Navigation Satellite Systems) and a tethered balloon.
The research activities presented in this work were carried out with contribution of the Next Generation EU funds within the National Recovery and Resilience Plan (PNRR), Mission 4-Education and Research, Component C2-From Research to Business (M4C2), Investment Line 1.1-Fund for the National research program and projects of significant national interest (PRIN), Project 2022JJJYTE -``Measuring tropospheric water vapor through the Normalized Differential Spectral Attenuation (NDSA) technique''
How to cite: Facheris, L., Argenti, F., Cuccoli, F., Cortesi, U., Del Bianco, S., Montomoli, F., Gai, M., Baldi, M., Barbara, F., Donati, A., Castelli, E., Papandrea, E., Achilli, A., Busetto, M., Calzolari, F., Melani, S., Viti, M., Ortolani, A., Antonini, A., and Rovai, L. and the Team of the University of Pisa, Dept. of Civil and Industrial Engineering, Pisa, Italy: Estimation of tropospheric water vapor using differential attenuation at microwaves and comparison with other measurements, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6583, https://doi.org/10.5194/egusphere-egu25-6583, 2025.
Retrieving the vertical distribution of tropospheric Ozone (O3) based on ground-based Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) observations presents challenges due to the interference of stratospheric O3 absorption. A Convolutional Neural Networks (CNN) method is proposed for retrieving the vertical distribution of tropospheric O3 based on ground-based MAX-DOAS observations. This method circumvents the issue of stratospheric O3 absorption interference when obtaining tropospheric O3 profiles by using CNN to extract features from MAX-DOAS spectral segments, enabling the retrieval of tropospheric O3 profiles. The core optimizations of this method are reflected in the following three aspects: (1) Enhancement of MAX-DOAS spectral features and establishment of a dataset with multiple features. To improve the feature extraction capability of the CNN model, mathematical methods are employed to enhance the features of the 320-340 nm spectral segments, which exhibit strong absorption characteristics for O₃. Additional datasets of various sensitive factors are incorporated to improve model inversion accuracy. The Z-Score normalization method is applied to unify dimensions and expedite model convergence, addressing inversion errors resulting from disparate dataset dimensions; (2) Constructing a PCA-F_Regression-SVR hybrid model to screen the optimal ancillary dataset for modeling. Principal Component Analysis (PCA) is utilized to reduce the dimensionality of all sensitive factors. A combination of Support Vector Regression (SVR) and the F_Regression function comprehensively evaluates and screens features sensitive to the tropospheric O₃ profiles retrieval. These features include profiles of temperature, specific humidity, fraction of cloud cover, eastward and northward winds, SO₂, NO₂, HCHO, as well as seasonal and temporal features; (3) The CNN inversion model is developed to extract the enhanced features from MAX-DOAS spectral segments and sensitive factors, enabling the retrieval of tropospheric O3 profiles. Aiming to minimize the loss function of the Mean Absolute Percentage Error (MAPE), the hyperparameters of the CNN inversion model are determined through cross-validation. The enhanced MAX-DOAS spectral features, along with sensitive factors, are used as the model inputs. The EAC4-CNEMC hybrid O3 profiles serve as the model outputs, resulting in a decrease in MAPE from 26% to 19%. The CNN inversion model is applied to independently retrieve tropospheric O3 profiles, and effectively reproduced the O3 profiles of the EAC4 dataset, exhibiting a Gaussian-like vertical distribution with peaks mainly around 950 hPa, and Absolute Percentage Errors (APEs) are generally controlled below 20%. In conclusion, leveraging MAX-DOAS spectra enables the retrieval of tropospheric O3 vertical distribution through the established CNN inversion model.
How to cite: Wang, Z., Tian, X., Xie, P., and Xu, J.: A Convolutional Neural Networks Method for Tropospheric Ozone Vertical Distribution Retrieval from Multi-AXis Differential Optical Absorption Spectroscopy Measurements, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3930, https://doi.org/10.5194/egusphere-egu25-3930, 2025.
To understand the dominant chemical mechanisms driving wintertime secondary PM2.5 formation and to validate GEMS L2 data, the National Institute of Environmental Research and the National Aeronautics and Space Administration (NASA) conducted the Airborne and Satellite Investigation of Asian Air Quality (ASIA-AQ) campaign across four Asian countries (Korea, the Philippines, Malaysia, and Thailand) from February to March 2024. During this campaign, we deployed six Pandora instruments, two AQProfilers, and five AERONET systems around the Seoul metropolitan region. Using these ground-based instruments, we retrieved nitrogen dioxide, ozone and formaldehyde vertical column densities, as well as aerosol properties, and compared the results with GEMS L2 products. A comparison of NO₂ observed by GEMS with that from ground-based remote sensing instruments revealed a correlation coefficient of over 0.6 across all regions. Additionally, a performance comparison of GEMS NO₂ across different versions showed that the overestimation observed in GEMS v2 results was improved in the v4 results. Furthermore, we also compared results from NASA GeoTASO with those from GEMS during this period.
How to cite: Hong, H., Jeong, U., Chang, L., Lee, H., Kim, S., and Kim, D.: GEMS L2 data validation during ASIA-AQ campaign, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15190, https://doi.org/10.5194/egusphere-egu25-15190, 2025.
