Displays

Within the scope of the VINDOBONA (VIenna horizontal aNd vertical Distribution OBservations Of Nitrogen dioxide and Aerosols) project, spectral UV/vis measurements at selected viewing directions are performed with three MAX-DOAS (Multi AXis Differential Optical Absorption Spectroscopy) instruments, which are located in the northeast, northwest, and south of the city center of Vienna, Austria. The selection of viewing directions of the three instruments was chosen in a way to provide data for the retrieval of horizontal and vertical trace gas and aerosol distributions, in particular over the urban core.

In the present work, the profile retrieval algorithm BOREAS (Bremen Optimal estimation REtrieval for Aerosols and trace gaseS) is used to retrieve aerosol and NO2 vertical profiles as well as accompanying parameters aerosol optical depth, tropospheric NO2 vertical columns (TVC NO2), and near-surface NO2 on days with cloudless conditions. The retrieval results are compared with co-located ceilometer, sun photometer, surface air quality, and TVC NO2 measurements, with the latter being obtained by applying the geometrical approximation and converting zenith-sky NO2 measurements.

How to cite: Schreier, S., Richter, A., Bösch, T., Lange, K., Revesz, M., Hilboll, A., Peters, E., Vrekoussis, M., Weihs, P., Schmalwieser, A., and Burrows, J.: Spatial and temporal distributions of NO2 and aerosols over the urban environment of Vienna during the VINDOBONA project (2017-2019), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14832, https://doi.org/10.5194/egusphere-egu2020-14832, 2020.

Increasing urbanization worldwide raise serious concerns about urban air quality and its effects on large human populations. This study presents application of the Differential Optical Absorption Spectroscopy technique to multi scale urban air quality (NO₂) monitoring. A Pandora spectroscopic instrument (SciGlob Inc) has been deployed on top of a 30 m building in Boston, MA, USA, since September 2019. It performs over the roof sky scans (local to meso scales), into the street canyon "target" (micro-scale), and direct sun measurements. In situ NO₂ measurements are also being conducted on top of the roof (co-located with Pandora) and at the street level near the "target" building. NO₂ spatial and temporal heterogeneity within different scales is discussed.

How to cite: Spinei, E., Geddes, J., Adams, T., Müller, M., and Gebetsberger, M.: Title: Urban air pollution monitoring at micro-, local and meso- scales using Pandora instrument, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20558, https://doi.org/10.5194/egusphere-egu2020-20558, 2020.

Nitrogen oxides (NO_x = NO + NO₂) have a direct and indirect impact on human health. Therefore, the World Health Organization recommends limiting the concentration of nitrogen dioxide (NO₂) in the atmosphere. Nevertheless, these limits are regularly exceeded. Especially, fossil fuel combustion from road traffic is a major contributor to the emission of NO_x.

Multi Axis-Differential Optical Absorption Spectroscopy (MAX-DOAS) is able to measure trace gases in the lower troposphere. Here, this remote sensing method was used to measure NO_x emissions at a highly frequented motorway. Two MAX-DOAS instruments were set up on both sides of the A60 motorway close to Mainz, Germany. The parallel viewing direction allows measuring the background signal at the upwind side and the background plus traffic emissions on the downwind side. Together with the effective wind speed perpendicular to the motorway, it is thus possible to retrieve the total traffic emissions. Compared to the expected emissions calculated from the European emission standards, the derived emissions of NO_x are by a factor 7±4 higher.

In this study, first measurement results are presented and the method is evaluated with regard to the practicability and error margin.

How to cite: Lauster, B., Dörner, S., Donner, S., Uhlmannsiek, K., Gromov, S., Beirle, S., and Wagner, T.: Estimating real driving emissions from MAX-DOAS measurements at the A60 motorway near Mainz, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1464, https://doi.org/10.5194/egusphere-egu2020-1464, 2020.

Oxygen-oxygen collision induced absorption accounts for significant absorption of solar radiation in the atmosphere. It needs to be considered in the interpretation of spectra in absorption spectroscopy. If not represented correctly, it interferes in the retrieval of other trace gases. Quantitative measurements of oxygen-oxygen collision induced absorption, combined with the oxygen concentration vertical profile, allow to constrain radiative transfer processes in the atmosphere. No spectrally resolved cross section data of the bands below 335 nm wavelength and at 420 nm have been available. This study presents spectrally resolved gas-phase laboratory measurements of the oxygen-oxygen collision induced absorption in the ultraviolet and blue spectral range (308 – 495 nm), including the 315, 328, and 421 nm bands, acquired with Cavity Enhanced Absorption Spectroscopy under atmospherically relevant conditions. While the newly acquired data generally agree with existing data on the strong bands, significant differences consist in a higher signal to noise ratio, a non-zero baseline between bands, and a different band shape of the 344 nm band. This presentation discusses the laboratory setup and analysis scheme used to determine the cross section, and first applications of the cross section to atmospheric data sets.

How to cite: Finkenzeller, H. and Volkamer, R.: Spectrally resolved laboratory measurements of oxygen-oxygen collision induced absorption in the 308 – 495 nm range, including the 315, 328, and 421 nm bands, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10089, https://doi.org/10.5194/egusphere-egu2020-10089, 2020.

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.

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.

How to cite: Tirpitz, J.-L., Frieß, U., and Platt, U.: The information content of skylight polarisation in MAX-DOAS trace gas and aerosol profiling applications, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10182, https://doi.org/10.5194/egusphere-egu2020-10182, 2020.

Since it provides vertically-resolved information on atmospheric gases at a horizontal scale approaching the one from nadir backscatter satellite sensors, the ground-based MAX-DOAS technique has been recognized as a valuable source of correlative data for validating space-borne observations of air-quality-related species such as NO₂, HCHO, SO₂, O₃, etc. In this context, the ESA Fiducial Reference Measurements for Ground-Based DOAS Air-Quality Observations (FRM₄DOAS) project is aiming at developing a near-real-time (6-24h latency) central processing system for the delivery of harmonized, quality-controlled, and fully traceable data products from MAX-DOAS instruments. The first phase of the project has been dedicated to the development of a prototype version of this processing system for 3 key products (NO₂ vertical profiles, total O₃ columns, and tropospheric HCHO profiles) and its demonstration at 11 project partners MAX-DOAS stations.

In this presentation we will describe the efforts carried out during the last months to develop the first MAX-DOAS central processing service to be operated within the Network for the Detection of Atmospheric Composition Change (NDACC). The main aspects of the service development will be presented, like the FRM₄DOAS prototype algorithm optimisation, operationalisation, and validation, and the establishment of MAX-DOAS NDACC instrument and data retrieval certification procedures, user data policy, datasets DOI, etc. This operational service is expected to be launched in Spring 2020 for a limited number (5-10) of NDACC-certified MAX-DOAS instruments. Corresponding data sets will be stored in the NDACC and ESA EVDC data handling facilities.

This activity and its future upscaling in terms of stations and data products will ensure that MAX-DOAS observations at a FRM quality level will be made available for the validation of present and future satellite missions like the Copernicus atmospheric Sentinels (5p, 4, 5).

How to cite: Hendrick, F., Fayt, C., Friedrich, M. M., Beirle, S., Frieẞ, U., Richter, A., Bösch, T., Kreher, K., Piters, A., Wagner, T., Tirpitz, J.-L., Bais, A., Prados Roman, C., Puentedura, O., Cede, A., Lind, E., Dehn, A., von Bismarck, J., Casadio, S., and Van Roozendael, M.: ESA FRM4DOAS: Towards the launch of the NDACC MAX-DOAS Central Processing Service, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19148, https://doi.org/10.5194/egusphere-egu2020-19148, 2020.

Pollutant concentration distribution and emission are important ways to understand regional pollution. To investigate the distribution characteristics and identify individual sources rapidly, a new mobile passive differential optical absorption spectroscopy (DOAS) instrument has been developed, which set two angle telescopes (90°,30°) to receive the scattered light respectively, and set two mechanical shutters to switch the optical path quickly in the mobile platform. The instrument collected the zenith scattered light in the UV or visible region and it was used to derive the vertical column density of trace gases above the measurement route. The slant column density in two different viewing directions were detected, and combined with the geometric approximation, the vertical column density of trace gas was obtained. After obtaining the column concentration distribution, the data were analyzed by semi variance analysis combined with geographical information. Monte Carlo simulation was used to reconstruct the high spatial resolution pollutant concentration distribution, combined the wind field data during the observation, the high spatial resolution emission flux in the area can be quickly obtained. A field experiment was performed in Beijing and some industrial area. The distribution information of vertical column density along the route in Beijing was derived, the concentration distribution of NO₂ at 200m *200m resolution and the 0.01° *0.01°resolution emission flux data are obtained further. The new mobile multi light DOAS instrument were operated on a car. The NO₂ column density spatial distribution and the emission flux spatial distribution are obtained with the maximum value of 8.57×1016 molec./cm² and 34.8 ug/m²/s over the Beijing fifth ring road area. The scheme can provide a new method to verify pollutant concentration distribution and emission inventory.

How to cite: Hu, Z., Li, A., and Xie, P.: Advanced mobile-DOAS techniuqes for locating and identifying urban area emission sources, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21242, https://doi.org/10.5194/egusphere-egu2020-21242, 2020.

For NO₂ monitoring by MAX-DOAS method, the automated instrument MARS-B based on the spectrograph ORIEL MS257 with a Peltier-cooled CCD-array detector Andor Technology DV-420 OE (number of active pixels is 1024×256, working temperature is -40 ºC) has been employed. The MARS-B instrument records the spectra of scattered sunlight in the range of elevation angles 0º – 90º within vertical angle aperture of 1.3º in spectral range 340-400 nm with FWHM = 0.32 nm and is operating without mechanical shutter. Radiation input system is working without optical fiber and spectrograph unit has open-air design, spectrograph unit is temperature-stabilized at level 40 ± 0.5 ºC. The MARS-B instrument successfully took part in MAD-CAT (2013) and CINDI-2 (2016) international inter-comparison campaigns.

Since 2017 MARS-B instrument is performing spectra registering over Minsk (National Ozone Monitoring Research and Education Centre, Minsk, Belarus) using multi-axis geometry of observations during daytime and zenith geometry in twilights. More than 4.5 millions of day-time spectra aiming to retrieve differential slant columns of ozone, nitrogen dioxide and oxygen dimer have been processed by DOAS method. Total nitrogen dioxide columns have been retrieved by PriAM algorithm which is based on optimal estimation method.

Continuous 3-year MAX-DOAS measurements (nitrogen dioxide vertical column, near-surface nitrogen dioxide concentrations, aerosol optical depth) over Minsk in period of 2017 - 2019 will be presented, compared with data of impact gas analyzers and satellite data, analyzed and discussed. Also, zenith twilights measurements will be processed aiming to retrieve stratospheric nitrogen dioxide and ozone columns for comparison with different parameters of solar activity.

How to cite: Bruchkouski, I., Barodka, S., and Wang, Y.: MAX-DOAS NO2 profile retrieval over Minsk: 3 years of observation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-700, https://doi.org/10.5194/egusphere-egu2020-700, 2020.

Africa experiences a fast urban inhabitants growth, caused by the largest population boom in the world, combined with rural exodus. Many cities are heavily affected by air pollution. It is therefore essential to monitor the concentrations of the various polluting species such as NO₂, HCHO, O₃ and aerosols, which have a direct impact on the population health. The sources of pollutant in Africa are different from those found in Europe. For example, forest fires and household cooking largely contribute to the NO₂ and HCHO burdens in Central Africa. However, many large African cities, such as the City of Kinshasa, capital of the Democratic Republic of Congo, do not have atmospheric measurement instruments.

In order to tackle the lack of measurements in Kinshasa, the Royal Belgian Institute of Space Aeronomy (BIRA-IASB) has, in collaboration with the University of Kinshasa (UniKin), installed an optical remote sensing instrument on the UniKin site (-4.42°S, 15.31°E). Installed in May 2017, the instrument has been in operation until today and provides data to measure the column amounts  of several polluting species in the atmosphere of Kinshasa. The instrument is based on a compact AVANTES  spectrometer covering the spectral range 290 - 450 nm with 0.7 nm resolution. The spectrometer is a Czerny-Turner type with an entry slit of 50 μm wide, and an array of 1200 l/mm. A 10 m long and 600 μm diameter optical fiber is connected to the spectrometer to receive the incident light beam from the sky. Measurements were mainly made by looking in a fixed direction until November 2019. Since then, a Multi-Axis geometry (MAX-DOAS) has been implemented.

The measurements provided by this DOAS instrument allowed us to start studying the atmosphere of Kinshasa using the QDOAS software, which allows us to find the oblique columns of different observed species.  This poster will present the instrument, the database and  the procedure used to convert these oblique columns into vertical columns, using the air mass factors calculated with the radiative transfer model. We also present our first MAX-DOAS results, analyzed using the retrieval tools of the ESA FRM4DOAS project. The study of current results clearly shows the signature of polluting species such as NO₂, HCHO in the atmosphere of Kinshasa. We also use simulations by the GEOS-Chem chemistry transport model to evaluate the magnitude of the emissions needed to explain the observed column amounts. These observations made in Kinshasa could contribute to the validation of satellite products and the refinement of models. We present a first comparison of Kinshasa's ground-based observations with those of the OMI and TROPOMI satellites

How to cite: Yombo Phaka, R., Merlaud, A., Pinardi, G., Fayt, C., Friedrich, M., Hendrick, F., Jacob, L., Van Roozendael, M., Mahieu, E., and Mbungu, J.-P.: DOAS measurements of NO2 and H2CO at Kinshasa and Comparisons with Satellites Observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1031, https://doi.org/10.5194/egusphere-egu2020-1031, 2020.

Multi-AXis (MAX)-DOAS instruments record spectra of scattered sun light under different elevation angles. From such measurements tropospheric vertical column densities (VCDs) and vertical profiles of different atmospheric trace gases and aerosols can be determined for the lower troposphere. These measurements allow a simultaneous observation of multiple trace gases (e.g. HCHO, CHOCHO, NO₂, etc.) with the same measurement setup. Since November 2018, a MAX-DOAS instrument is operated at the Bayfordbury Observatory, which is located approximately 30 km north of London. This measurement site is operated by the University of Hertfordshire and equipped with an AERONET station, a LIDAR and multiple instruments to measure meteorological quantities and solar radiation. Depending on the prevailing wind direction the air masses at the measurement site can be dominated by the pollution of London (SE to SW winds) or rather pristine air (northerly winds). Therefore, this measurement site is well suited to study the influence of anthropogenic pollution on the atmospheric composition and chemistry at a rather pristine location in the vicinity of London, a major European capital with 9.8 million inhabitants and 4 major international airports.

In this study, trace gas and aerosol profiles are retrieved using the MAinz Profile Algorithm MAPA (Beirle et al., 2018) with a focus on tropospheric formaldehyde (HCHO) which plays an important role in tropospheric chemistry. The HCHO results are combined with the results of other trace species such as NO₂, CHOCHO and aerosols in order to identify different chemical regimes and pollution levels.

How to cite: Donner, S., Dörner, S., Buxmann, J., Beirle, S., Campbell, D., Müller, D., Remmers, J., Rolfe, S. M., and Wagner, T.: One year of MAX-DOAS measurements of tropospheric trace gases and aerosols in the suburban area of London, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3323, https://doi.org/10.5194/egusphere-egu2020-3323, 2020.

Atmospheric pollution has a well-known impact on the human life, thus observing the emissions of trace gases is an important part of monitoring the atmospheric composition. This paper aims to determine the vertical column densities (VCDs) of Nitrogen Dioxide (NO₂) and Sulfur Dioxide (SO₂). These quantities will be used to calculate emissions of these pollutants quantified using a ground based mobile remote sensing technique that relies on scattered light DOAS (Differential Optical Absorption Spectroscopy) measurements. This method will be implemented using the SWING (Small Whiskbroom Imager for atmospheric compositioN monitorinG). The instrument is designed to perform airborne measurements, but for the purpose of this paper it was adapted for ground-based use by the National Institute for Aerospace Research (INCAS) in Bucharest, Romania. The source aimed to be quantified is the city of Bucharest, specifically the total emissions generated by the traffic and industry within the city. The measurements will be performed during the Spring of 2020 between February and April. The experimental setup consists of the SWING that will be mounted on the roof of a car, which allows to perform measurements along the ring road of Bucharest. There will be presented results from several days of measurements from a total of 150 hours of driving in terms of differential slant column densities (DSCDs), vertical column densities (VCDs) and quantified emissions of NO­₂ and SO₂. This study will also be used for the fine tuning of the SWING operational parameters for use on UAV platforms in future measurement campaigns.

How to cite: Iancu, S.: Quantification of Nitrogen Dioxide and Sulfur Dioxide emissions from Bucharest using a mobile-DOAS setup, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3616, https://doi.org/10.5194/egusphere-egu2020-3616, 2020.

Measurements of the atmospheric absorption of the oxygen dimer O₄ are often used to characterize the atmospheric light paths, e.g. to derive properties of clouds and aerosols. Some recent studies indicated discrepancies between measurements and simulations of the atmospheric O₄ absorption, while others found exact quantitative agreement. One difficulty in these studies was to correctly represent the aerosol properties in the radiative transfer simulations, e.g. due to lack of information about the vertical profiles or scattering properties.

In this study we investigate MAX-DOAS measurements of the atmospheric O₄ absorption during a ship cruise in April and May 2019 over the tropical Atlantic. The elevation angle of the instruments telescope is automatically stabilized in order to compensate the motion of the sea. We select measurements on one day (2 May 2019) with extremely low aerosol optical depth (between about 0.03 and 0.05 at 360 nm). For such conditions the atmospheric scattering processes are dominated by Rayleigh scattering on air molecules.

Besides the MAX-DOAS measurements, also measurements by a ceilometer and sun photometer are available, which are used to constrain the atmospheric aerosol properties. The radiative transfer simulations are carried out with the full spherical radiative transfer model MCARTIM.

How to cite: Wagner, T., Dörner, S., Donner, S., Beirle, S., and Kinne, S.: Quantitative comparison of measured and simulated O4 absorption for one day with extremely low aerosol load over the tropical Atlantic, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4237, https://doi.org/10.5194/egusphere-egu2020-4237, 2020.

Multi-AXis Differential Optical Absorption Spectroscopy has become a versatile and mature measurement technique for determining various components of the Earth’s atmosphere, e.g. O₃, SO₂, NO₂ properties. Since the concentration of these trace gases might strongly vary locally and in time, easy in-situ measurements with a mobile device are highly desirable.

We are currently developing a portable MAX-DOAS instrument setup consisting of three small telescopes with a diameter of 50mm. Each of these telescopes is equipped with an individual fiber-fed low-resolution spectrograph (Stellarnet Blue Wave devices, 2048 pixel CCD) to enable simultaneous measurements ranging from 300 to 1000nm in one shot. The entire wavelength range is therefore covered by three spectral arms: (a) The UV arm, equipped with a Stellarnet BLUE-Wave UV2 spectrograph ranging from 300 to 500nm; (b) the VIS arm consisting of a NIR4 device (500…700nm), and (c) The NIR arm, based on a Stellarnet NIR2 ranging from 600 to 1000nm. All spectrographs are fed with wavelength-optimised fibers and equipped with the smallest possible slit (14 µm slit width) to maximise the throughput and the spectral resolving power (λ-dispersion UVB + VIS: 0.2nm; NIR: 0.4nm).

The three telescopes are aligned in parallel and installed on a small astronomical azimuthal mount (Skywatcher AZ-EQ5, powered by a mobile 12V Lithium-Polymer battery) to enable measurements in all directions. The mount control software will be based either on the ASCOM or the INDILIB platform. For the control of the spectrographs we use the programme SpectraWiz (by Stellarnet). As DOAS analysis software we have chosen QDOAS, provided by the Royal Belgian Institute for Space Aeronomy. All software is freely available and is installed on a Dell Latitude 5450 Rugged laptop, which is optimised for outdoor applications.

The chosen setup enables a mobile usage easily transportable by a small car. Since the development is currently ongoing, especially with respect to the automation of the measurements and the data processing, we report on the status of the project in this presentation.

How to cite: Kausch, W., Kimeswenger, S., Przybilla, N., and Noll, S.: Development of a versatile portable MAX-DOAS instrument, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4552, https://doi.org/10.5194/egusphere-egu2020-4552, 2020.

For the last decades, civil aviation traffic increased rapidly. At Frankfurt airport more than 700 flights depart per day (5h to 23h) i.e., take-offs take place approximately every two minutes. Like many other engines, an airplane’s engine uses fossil fuel primarily emitting carbon dioxide (CO₂) and water vapour (H₂O). However, high combustion temperatures also lead to a significant amount of nitrogen oxide (NO_x) emission. NO_x has a large impact on atmospheric chemistry and is harmful to human health. As airports are usually built in highly populated areas, these pollutants affect the health of the inhabitants in the region. Only few measurements have directly investigated emissions of airplanes under real atmospheric conditions during take-off as these measurements are typically difficult to perform.

In this work, we show the applicability and first results using Multi AXis Differential Absorption Spectroscopy (MAX-DOAS) measurements to directly determine airplane emissions during take-off at Frankfurt airport. Therefore, the MAX-DOAS instrument is mounted in extension of the runway, about 500 m below the typical altitude of the departing aircrafts to measure a spectrum of scattered sun light through the exhaust plume. Using a wide aperture of the entrance optics at one fixed elevation instead of scanning across the plume allows capturing the whole plume with one simultaneous measurement. In that way, the induced NO₂ emission of each passing aircraft can be determined. The obtained NO₂ emissions are then used to estimate the total emissions of nitrogen oxides. 

How to cite: Uhlmannsiek, K., Lauster, B., Dörner, S., Donner, S., Beirle, S., and Wagner, T.: Estimating aircraft emissions at Frankfurt airport using the DOAS technique, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6671, https://doi.org/10.5194/egusphere-egu2020-6671, 2020.

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.

Ship measurements of Nitrogen Dioxide (NO₂) and Sulphur Dioxide (SO₂) 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.

How to cite: Dörner, S., Ruhtz, T., Donner, S., Beirle, S., Kinne, S., and Wagner, T.: Tropospheric trace gas slant column densities derived from MAX-DOAS measurements on pacific transit cruises of the German research vessel Sonne in 2019, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6980, https://doi.org/10.5194/egusphere-egu2020-6980, 2020.

Imaging of atmospheric trace gases is becoming an increasingly important field of remote sensing. Conventional methods (like imaging-DOAS) typically use dispersive elements and wavelength mapping (at moderate to high spectral resolution) and need intricate optical setup. Therefore, they are limited in spatio-temporal resolution.

Some atmospheric trace gases can, however, be detected only by using a few carefully selected spectral channels, specific to the selected trace gas. These can be filtered using non-dispersive spectral filters without spatial mapping of continuous spectra, vastly increasing the spatio-temporal resolution. This has become a routine in volcanic SO₂ flux analysis, where band-pass filters provide the spectral filtering.

We propose fast imaging of spatial Nitrogen Dioxide (NO₂) distributions employing Gas Correlation Spectroscopy (GCS) in the visible wavelength range. Two spectral channels are used, one with a gas cell that is filled with a high amount of NO₂ in the light path and one without. An additional band-pass filter preselects a wavelength range containing structured and strong NO₂ absorption (e.g. 430 - 450 nm). The NO₂ containing gas cell serves as a NO₂ specific spectral filter, almost blocking the light at wavelengths of the strong NO₂ absorption bands within the preselected wavelength range. Absorption by atmospheric NO₂ has therefore a lower impact on the channel with gas cell compared to the channel without gas cell. This difference is used to generate NO₂ images.

NO₂ plays a major role in urban air pollution, where it is primarily emitted by point sources (power plants, vehicle internal combustion engines), before undergoing chemical conversions. The corresponding spatial gradients can neither be resolved with the established in-situ techniques nor with the widely used DOAS remote sensing method.

Recent advances in the physical implementation of a GCS-based NO₂ camera suggest, that the quality of the measurement may be vastly enhanced in a two-detector (two-camera) set-up. Here, individual cameras are used for the two spectral channels. Not only does this double the photon budget available, but it also allows for synchronized exposure in both channels. This is critical for the quality of the measurement, since dynamic gas or intensity features on time scales smaller than the exposure delay of a one-camera system can induce strong false signals.

A proof of concept measurement was carried out, where test cells with NO₂ column densities ranging from 1E16 to 4E18 molecules cm^-2 were measured both with DOAS and our camera. The results coincided within their uncertainties and allow for camera calibration based on an instrument forward model.

How to cite: Kuhn, L., Kuhn, J., Wagner, T., and Platt, U.: A two-camera instrument for highly resolved Gas Correlation Spectroscopy measurements of NO2, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7194, https://doi.org/10.5194/egusphere-egu2020-7194, 2020.

Within the project VINDOBONA (VIenna horizontal aNd vertical Distribution OBservations Of Nitrogen dioxide and Aerosols), a method was developed to retrieve the spatial distribution of trace gases using data from three ground based MAX-DOAS instruments and was applied on the example of NO₂. At three different locations in Vienna (Austria) MAX-DOAS instruments were installed performing measurements in the visible and UV spectral range. Currently, each instrument is set up to determine the column densities in different azimuthal directions and low elevation angles within approximately a horizontal plane. The different lines of sight of the three instruments intersect horizontally and can be used to estimate the horizontal spatial distribution of trace gases. With the knowledge of vertical profiles, even the vertical distribution can be estimated using this method. 

The intersections of the different lines of sight define segments along the slant columns for which the mass concentrations can be estimated. Knowledge about the vertical profiles for a chosen trace gas can be used to correct the retrieved trace gas concentration to specific altitudes above ground. Such corrections are also required since the three instruments were set up at different heights above ground, at different altitudes relative to sea level and with different elevation angles of the lowest viewing direction. One open issue for the retrieval process is the terrain in Vienna in combination with the prevailing wind condition that impacts the horizontal and vertical trace gas distribution and make the retrieval challenging. 

How to cite: Revesz, M., Schreier, S. F., Weihs, P., Bösch, T., Lange, K., Richter, A., Vrekoussis, M., and Schmalwieser, A. W.: A method for retrieving the spatial distribution of trace gases using measurements of three ground-based MAX-DOAS instruments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8792, https://doi.org/10.5194/egusphere-egu2020-8792, 2020.

We present the Airyx 2D SkySpec Instrument: A commercially available two-dimensionally scanning Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) setup for the observations of trace gases using spectral measurements of scattered sun light and optionally also direct sun light. The waterproof design of the scanner unit is designed for long-term outdoor deployment. Temperature stabilisation of the spectrometers and automatic calibration spectra measurement are used to ensure high-quality measurement data over months and years of observations.

We show 2.5 years of measurements in Munich. Vertical columns and vertical distribution profiles of aerosol extinction coefficient, NO₂ and HCHO are retrieved from the 2D MAX-DOAS observations. The measured surface aerosol extinction coefficients and NO₂ mixing ratios are compared to in-situ monitor data. The retrieved surface NO₂ mixing ratios show good agreement with in-situ monitor data with a Pearson correlation coefficient (R) of 0.91. Good agreement (R= 0.80) is also found for AOD when compared to sun-photometer measurements. Tropospheric vertical column densities (VCDs) of NO2 and HCHO derived from the MAX-DOAS measurements are also used to validate OMI and TROPOMI satellite observations. Monthly averaged data show good correlation, however, satellite observations are on average 30% lower than the MAX-DOAS measurements. Furthermore, the 2D MAX-DOAS observations are used to investigate the spatio-temporal characteristic of NO2 and HCHO in Munich. Analysis of the relations among aerosol, NO₂ and HCHO show higher aerosol to HCHO ratios in winter indicating a longer atmospheric lifetime of aerosol and HCHO. The analysis also suggests that secondary aerosol formation is the major source of aerosols in Munich.

How to cite: Lampel, J., Chan, K. L., Pöhler, D., Wiegner, M., Alberti, C., Platt, U., and Wenig, M.: The Airyx 2D SkySpec instrument: MAX-DOAS measurements of tropospheric NO2 and HCHO in Munich and the comparison to satellite observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8941, https://doi.org/10.5194/egusphere-egu2020-8941, 2020.

Lahore, megacity of Pakistan with more than 11 million inhabitants is a strong emission source of atmospheric pollutants. We present results of a top-down emission procedure for NOx and SO₂ for Lahore, based on car multi-axis differential optical absorption spectroscopy (car-MAX-DOAS) observations. Additionally, the total flux of HCHO from the city is determined which can be seen as an indicator for VOC emissions. Results from two extensive campaigns, which took place in summer 2017 and spring 2018 will be presented. From the measured spectra, we retrieve the vertically integrated concentration (the so-called tropospheric vertical column density, VCD) of the trace gases along the driving route by using the so-called geometric approximation method. By combining these observations with ECMWF Re-Analysis wind data, the total fluxes of NO_x, SO₂ and HCHO from the city of Lahore are estimated. From both measurement campaigns, we also analyzed the seasonal variability of the above-mentioned species.

Derived NOx and SO₂ emissions are compared to the bottom-up emission inventory EDGAR. Spatial disributions of the tropospheric NO₂ and SO₂ VCDs observed by car MAX-DOAS are compared with those simulated using a coupled regional-global model system (MECO(n)). We find that, the model is able to account for the spatial variablity but the VCDs are systematically underestimated by the regional model. Finally, derived NOx emissions are also compared to the emissions estimated from TROPOMI satellite observations.

How to cite: Razi, M., Dörner, S., Kumar, V., Donner, S., Ahmad, N., Beirle, S., Khokhar, M. F., and Wagner, T.: Estimation of NOx, SO2 and HCHO emissions from the megacity of Lahore, Pakistan using car MAX-DOAS observations and comparison with regional model and TROPOMI satellite data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9265, https://doi.org/10.5194/egusphere-egu2020-9265, 2020.

MAX-DOAS observations was carried out from March 1, 2019 to December 31, 2019 in Qingdao, China, to measure the O₄, NO₂, SO₂ and H₂O absorption, to retrieve AOD and the troposphere vertical column concentration of NO₂, SO₂ and H₂O.We use PriAM algorithm which based on the optimal estimation to calculating volume mixing ratio profile of trace gases, aerosol and water vapor during 0 ~ 4 km. The correlation between AOD and H₂O VCD was analyzed in every month, the results showed that the AOD and H₂O VCD has good linear relationship in each month., illustrate the increase of water vapor concentration will lead to the increase of moisture absorption of aerosol. The seasonal variation of the four seasonal correlation slopes in the order of summer < autumn < spring < winter. The influence of concentration change of NO₂ VCD, SO₂ VCD, H₂O VCD and AOD is discussed in a haze episodes occurred in December 2019. Discovery that the H₂O VCD and AOD was increased at the same time in the haze pollution incident, but with the increase of water vapor concentration, the concentration of NO₂ and SO₂ decreases, indicated that due to the increase of concentration of water vapor, NO₂ and SO₂ heterogeneous reaction will happen to generate nitrate and sulfate aerosols, so that the concentration of NO₂ and SO₂ concentration was decreased. The relationship between NO₂, SO₂, AOD and water vapor mixing ratio of 50m, 200m, 400m and 600m during haze pollution period was also studied, and it was indicated that phenomenon aerosol extinction increased with the increase of water vapor mixing ratio, while NO₂ and SO₂, on the contrary, were more obvious at 50m and 200m near the ground.

How to cite: Ren, H., Li, A., Hu, Z., Huang, Y., Xu, J., and Xie, P.: The seasonal correlation between atmospheric water vapor and aerosol extinction and the relationship between aerosol, NO2, SO2 and water vapor during haze pollution in Qingdao, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12714, https://doi.org/10.5194/egusphere-egu2020-12714, 2020.

Atmospheric aerosols range in diameter from a few nanometers to tens of micrometers, and they have direct or indirect effects on atmospheric radiation assessments, global climate change, local air quality and visibility, and human health. In particular, during the high season of haze in autumn and winter, atmospheric aerosols are more conducive to transform and accumulate. In this paper, we used the aerosol optical thickness (AOD) and aerosol profile obtained by MAX-DOAS instrument to study the characteristics of aerosol-type, vertical distribution characteristics of near-surface aerosol, and pollution source analysis. From December 30, 2018, to January 27, 2019, we conducted MAX-DOAS observations on Sanmenxia Environmental Protection Bureau. According to the relative humidity data and ion chromatography data, we analyzed the correlation between AOD and PM_2.5, the result show that aerosols are mainly fine particles, and most of them are nitrates. The near-surface aerosol extinction coefficient obtained by MAX-DOAS was compared with the PM_2.5 and PM₁₀ concentrations measured by unmanned aerial vehicle (UAV). Aerosol particles showed an increasing trend from the ground to 500 m. Combined with the wind field information and the backward trajectory of the air mass during the haze, we found that the continuous heavy pollution was caused by the transportation of polluted air masses in the northeast, along with local industrial emissions and other sources of emissions, which resulted in a wide range and long-term accumulation of pollutants under continuous and steady conditions.

How to cite: Li, X., Xie, P., and Li, A.: Study of aerosol-type characteristics and sources using MAX-DOAS measurement during haze at an urban site in the Fenwei Plain, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12726, https://doi.org/10.5194/egusphere-egu2020-12726, 2020.

Ground-based Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements of aerosols, tropospheric nitrogen dioxide (NO₂) and formaldehyde (HCHO) have been carried out in Uccle, Brussels, during two years (March 2018 – March 2020). The MAX-DOAS instrument has been operating in both UV and visible (Vis) wavelength ranges in a dual-scan configuration consisting of two sub-modes: (1) an elevation scan in a fixed viewing azimuthal direction (the so-called main azimuthal direction) pointing and (2) an azimuthal scan in a fixed low elevation angle (2^o). By applying a vertical profile inversion algorithm in the main azimuthal direction and an adapted version of the parameterization technique proposed by Sinreich et al. (2013) in the other azimuthal directions, near-surface  concentrations (VMRs) and vertical column densities (VCDs) are retrieved in ten different azimuthal directions.

The present work focuses on the seasonal horizontal variation of NO₂ and HCHO around the measurement site. The observations show a clear seasonal cycle of these trace gases. An important application of the dual-scan MAX-DOAS measurements is the validation of satellite missions with high spatial resolution, such as TROPOMI/S5P. Measuring the tropospheric  VCDs in different azimuthal directions is shown to improve the spatial colocation with satellite measurements leading to a better agreement between both datasets. By using  vertical profile information derived from the MAX-DOAS measurements, we show that a persistent systematic underestimation of the TROPOMI  data can be explained by uncertainties in the a-priori NO₂ profile shape in the satellite retrieval. A similar validation study for TROPOMI HCHO is currently under progress and preliminary results will be presented.

References:

Sinreich, R., Merten, A., Molina, L., and Volkamer, R.: Parameterizing radiative transfer to convert MAX-DOAS dSCDs into near-surface box-averaged mixing ratios, Atmos. Meas. Tech., 6, 1521–1532, https://doi.org/10.5194/amt-6-1521-2013, 2013.

How to cite: Dimitropoulou, E., Hendrick, F., Friedrich, M. M., Pinardi, G., Tack, F., Merlaud, A., Fayt, C., Hermans, C., Fierens, F., and Van Roozendael, M.: Tropospheric NO2 and HCHO derived from dual-scan MAX-DOAS measurements in Uccle (Belgium) and application to S5P/TROPOMI validation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17181, https://doi.org/10.5194/egusphere-egu2020-17181, 2020.

In many spectroscopic applications, optical fibres are an essential part of the instrumental setup. One of such applications is Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS), which is a remote sensing technique to detect atmospheric aerosol and trace gases by analysing spectra of scattered skylight. Typically, multi-mode quartz fibres (MMQF) of > 100 µm in diameter are used in MAX-DOAS instruments to interconnect the telescope unit with a grating spectrometer. Besides acting as a light guide giving more freedom in the spatial arrangement of telescope and spectrometer and homogenizing the illumination of the spectrometer entrance slit, such fibres have depolarising properties originating predominantly from manufacturing induced birefringent effects. This property is particularly desirable in MAX-DOAS applications, since the incoming partially polarized skylight should ideally be depolarized before entering the polarisation sensitive spectrometer. The behaviour of polarised light in mono-mode fibres is well investigated and even utilized in telecommunications, whereas equivalent literature on multi-mode fibres is scarce.

We measured the depolarisation capabilities of a set of 20 MMQF of different age, length and diameter as typically used in MAX-DOAS applications. Independent of the fibre diameter, we found that in some recently manufactured (in 2018) fibres polarisation is well preserved with a decrease in total degree of polarisation (DOLP) to 1/e of its initial value at a fibre length L_e > 10 m at 450 nm, while in older fibres (> 10 years in age) L_e ≈ 1 m was found. This is probably due to improvements in the manufacturing process in the recent years. We further investigated the dependence of L_e on wavelength, on the polarisation orientation of the ingoing light and on additional birefringence induced by applying external strain (bending) to the fibres. The results are presented and discussed with regard to their implications for MAX-DOAS observations.

How to cite: Oehmke, V., Tirpitz, J.-L., Frieß, U., and Platt, U.: Polarisation preservation in multi-mode optical quartz fibres and implications for MAX-DOAS observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18047, https://doi.org/10.5194/egusphere-egu2020-18047, 2020.

As part of the German project MeSMarT (Measurements of shipping emissions in the marine troposphere, a cooperation between the University of Bremen and the German Federal Maritime and Hydrographic Agency) and the EU LIFE project CLINSH (Clean Inland Shipping,) numerous mobile measurements of atmospheric trace gases and aerosols have been carried out.

For both projects one main objective is to investigate the general impact of shipping emissions on the air quality in regions with high marine traffic. In order to do this in areas where no permanent monitoring systems are available, in 2015 a mobile lab has been set up, which includes among other instrumentation for air pollution and meteorological parameters a scientific-grade MAX-DOAS system as well as in situ instruments for nitrogen oxides, ozone, carbon monoxide and sulfur dioxide (trace level).

In this study we present intercomparison results between the different instruments onboard the mobile lab as well as the interpretation of the results using complementary data sets at different locations including the Lower Rhine and Waal area and several regions in Northern Germany. For some places close to the banks of the Rhine more than 70% of the nitrogen oxides are related to shipping emissions. Emission factors for different ship types have been calculated and compared to recent studies and emission inventories.

How to cite: Wittrock, F., Krause, K., Lange, K., Seyler, A., Richter, A., and Burrows, J. P.: Mobile MAX-DOAS and in situ measurements of atmospheric trace gases and aerosols, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20025, https://doi.org/10.5194/egusphere-egu2020-20025, 2020.

As part of the TROLIX'19 (TROpomi vaLIdation eXperiment) campaign (2 September to 4 October 2019), measurements of tropospheric NO₂ columns and surface concentrations were made using the MAX-DOAS (Multi-AXis Differential Optical Absorption Spectroscopy) technique. To characterise any TROPOMI sub pixel (less than 3.5 km x 7 km) heterogeneity, four MAX-DOAS instruments were deployed at rural locations close to Cabauw (51.97°N, 4.93°E) and further six instruments were operated within the highly industrialized area of Rotterdam (51.92°N, 4.48°E) in the Netherlands. All instruments performed sky scanning from the horizon (from approximately 1°) to the zenith. In addition, two of the MAX-DOAS instruments (Pandoras) also measured total NO₂ columns in direct sun mode.

Here we present first results focusing on the measurements of NO₂ spatial gradients made at sites within approximately 3-10 km distance in a rural and an urban environment. The data analysis was done in two steps. Differential slant column densities were calculated using the data processing procedures established during the CINDI-2 intercomparison campaign (Kreher et al., in review, 2019) in UV and VIS spectral ranges. Tropospheric columns, near surface concentrations and profiles were then calculated using the Pandora real time algorithm as well as the NDACC UV-Vis Central Processing system developed in the ESA FRM₄DOAS project. Local heterogeneity at the surface level was evaluated using in-situ NO₂ measurements available from several routine monitoring stations within the area of interest. The local NO₂ heterogeneity effect on TROPOMI validation is also discussed.

Reference:

Kreher, K. et al.: Intercomparison of NO₂, O₄, O₃ and HCHO slant column measurements by MAX-DOAS and zenith-sky UV-Visible spectrometers during the CINDI-2 campaign, Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2019-157, in review, 2019.

How to cite: Kreher, K., Spinei, E., Piters, A., Apituley, A., Bais, A., Doerner, S., Fayt, C., Friedrich, M., Frumau, A., Hendrick, F., Hermans, C., Karagkiozidis, D., Querel, R., Van Roozendael, M., Vonk, J., and Wagner, T.: MAX-DOAS measurements of atmospheric rural and urban NO2 gradients during the TROLIX'19 campaign, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20796, https://doi.org/10.5194/egusphere-egu2020-20796, 2020.

Nanjing, as one of the important cities in the Yangtze River Delta of China, has a developed economy and a large population. Although the concentration of air pollutants in Nanjing has declined with the introduction of China’s strict air pollution prevention and control policies, the situation of air pollution is still severe. Therefore, understanding the source and distribution of atmospheric pollutants has an important role in implementing the prevention and controlling of atmospheric pollutants. In this study, we observed the vertical distribution characteristics of tropospheric NO₂ by used the ground-based Multi Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) technique in Nanjing. The contribution of transregional transport to NO₂ in different seasons and different altitudes (200m, 500m, and 1000m) was analyzed by combining the potential source distribution model (PSCF). The analysis results showed that the distribution of NO₂ sources were obvious seasonal changes. Due to the lower wind speed in spring, the distribution of NO₂ sources at all altitudes was not obvious. In summer and autumn, the source of NO₂ in the lower altitudes (200m) was concentrated in the urban area of ​​Nanjing and central Jiangsu Province. But for the winter, the NO₂ concentrations of lower altitudes were seriously affected by Chuzhou and Ma'anshan area. The sources distribution in the middle and upper altitude were relatively scattered and the WPSCF value was smaller than lower altitudes, which may be caused by the NO₂ concentrated in the near ground.

How to cite: ren, B., Xie, P., Xu, J., Li, A., Tian, X., Hu, Z., and Li, X.: Research on measurement and source distribution of atmospheric NO2 concentration by ground-based MAX-DOAS system in Nanjing, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21086, https://doi.org/10.5194/egusphere-egu2020-21086, 2020.