Equations for solar tracking

Direct Sun light absorption by trace gases can be used to quantify them and investigate atmospheric chemistry. In such experiments, the main optical apparatus is often a grating or a Fourier transform spectrometer. A solar tracker based on motorized rotating mirrors is also needed to direct the light along the spectrometer axis, correcting for the apparent rotation of the Sun. Calculating the Sun azimuth and altitude for a given time and location can be achieved with high accuracy but different sources of angular offsets appear in practice when positioning the mirrors. A feedback on the motors, using a light position sensor closed to the spectrometer is almost always needed. This paper aims to gather the main geometrical formulas necessary for the use of a widely used kind of solar tracker, based on two 45{\deg} mirrors in altazimuthal set-up with a light sensor on the spectrometer, and to illustrate them with a tracker developed for atmospheric research by our group.Comment: 14 pages, 7 figures. Second version of the paper as published in Sensors. Main correction: a rotation matrix converted to a reflection matrix. Main addition: a discussion on how the control theory applies to this kind of tracking syte

Constraining industrial ammonia emissions using hyperspectral infrared imaging

Atmospheric emissions of reactive nitrogen in the form of nitrogen dioxide (NO) and ammonia (NH) worsen air quality and upon deposition, dramatically affect the environment. Recent infrared satellite measurements have revealed that NH emitted by industries are an important and underestimated emission source. Yet, to assess these emissions, current satellite sounders are severely limited by their spatial resolution. In this paper, we analyse measurement data recorded in a series of imaging surveys that were conducted over industries in the Greater Berlin area (Germany). On board the aircraft were the Telops Hyper-Cam LW, targeting NH measurements in the longwave infrared at a resolution of 4 m and the SWING+ spectrometer targeting NO measurements in the UV–Vis at a resolution of 180 m. Two flights were carried out over German’s largest production facility of synthetic NH , urea and other fertilizers. In both cases, a large NH plume was observed originating from the factory. Using a Gaussian plume model to take into account plume rise and dispersion, coupled with well-established radiative transfer and inverse methods, we retrieve vertical column densities. From these, we calculate NH emission fluxes using the integrated mass enhancement and cross-sectional flux methods, yielding consistent emissions of the order of 2200 t yr−1 for both flights, assuming constant fluxes across the year. These estimates are about five times larger than those reported in the European Pollutant Release and Transfer Register (E-PRTR) for this plant. In the second campaign, a co-emitted NO plume was measured, likely related to the production of nitric acid at the plant. A third flight was carried out over an area comprising the cities of Staßfurt and Bernburg. Several small NH plumes were seen, one over a production facility of mineral wool insulation, one over a sugar factory and two over the soda ash plants in Staßfurt and Bernburg. A fifth and much larger plume was seen to originate from the sedimentation basins associated with the soda ash plant in Staßfurt, indicating rapid volatilization of ammonium rich effluents. We use the different measurement campaigns to simulate measurements of Nitrosat, a potential future satellite sounder dedicated to the sounding of reactive nitrogen at a resolution of 500 m. We demonstrate that such measurements would allow accurately constraining emissions in a single overpass, overcoming a number of important drawbacks of current satellite sounders

The Small Whiskbroom Imager for atmospheric compositioN monitorinG (SWING) and its operations from an unmanned aerial vehicle (UAV) during the AROMAT campaign

The Small Whiskbroom Imager for atmospheric compositioN monitorinG (SWING) is a compact remote sensing instrument dedicated to mapping trace gases from an unmanned aerial vehicle (UAV). SWING is based on a compact visible spectrometer and a scanning mirror to collect scattered sunlight. Its weight, size, and power consumption are respectively 920g, 27cm × 12cm × 8cm, and 6W. SWING was developed in parallel with a 2.5m flying-wing UAV. This unmanned aircraft is electrically powered, has a typical airspeed of 100km h−1, and can operate at a maximum altitude of 3km. We present SWING-UAV experiments performed in Romania on 11 September 2014 during the Airborne ROmanian Measurements of Aerosols and Trace gases (AROMAT) campaign, which was dedicated to test newly developed instruments in the context of air quality satellite validation. The UAV was operated up to 700m above ground, in the vicinity of the large power plant of Turceni (44.67°N, 23.41°E; 116m a. s. l. ). These SWING-UAV flights were coincident with another airborne experiment using the Airborne imaging differential optical absorption spectroscopy (DOAS) instrument for Measurements of Atmospheric Pollution (AirMAP), and with ground-based DOAS, lidar, and balloon-borne in situ observations. The spectra recorded during the SWING-UAV flights are analysed with the DOAS technique. This analysis reveals NO2 differential slant column densities (DSCDs) up to 13±0.6×1016molec cm−2. These NO2 DSCDs are converted to vertical column densities (VCDs) by estimating air mass factors. The resulting NO2 VCDs are up to 4.7±0.4×1016molec cm−2. The water vapour DSCD measurements, up to 8±0.15×1022molec cm−2, are used to estimate a volume mixing ratio of water vapour in the boundary layer of 0.013±0.002mol mol−1. These geophysical quantities are validated with the coincident measurements

MAX-DOAS measurements of NO2 and H2CO in the city of Kinshasa from 2019 2020

The first MAX-DOAS measurements of NO2 and H2CO were presented in this study. A preliminary comparison with TROPOMI is also presente

Validation of Sentinel-5P TROPOMI tropospheric NO2 products by comparison with NO2 measurements from airborne imaging, ground-based stationary, and mobile car DOAS measurements during the S5P-VAL-DE-Ruhr campaign

Airborne imaging differential optical absorption spectroscopy (DOAS), ground-based stationary and car DOAS measurements were conducted during the S5P-VAL-DE-Ruhr campaign in September 2020. The campaign area is located in the Rhine-Ruhr region of North Rhine-Westphalia, Western Germany, which is a pollution hotspot in Europe comprising urban and large industrial emitters. The measurements are used to validate space-borne NO2 tropospheric vertical column density data products from the Sentinel-5 Precursor (S5P) TROPOspheric Monitoring Instrument (TROPOMI). Seven flights were performed with the airborne imaging DOAS instrument for measurements of atmospheric pollution (AirMAP), providing measurements which were used to create continuous maps of NO2 in the layer below the aircraft. These flights cover many S5P ground pixels within an area of 30 km x 35 km and were accompanied by ground-based stationary measurements and three mobile car DOAS instruments. Stationary measurements were conducted by two Pandora, two zenith-sky and two MAX-DOAS instruments distributed over three target areas. Ground-based stationary and car DOAS measurements are used to evaluate the AirMAP tropospheric NO2 vertical column densities and show high Pearson correlation coefficients of 0.87 and 0.89 and slopes of 0.93 &plusmn; 0.09 and 0.98 &plusmn; 0.02 for the stationary and car DOAS, respectively. Having a spatial resolution of about 100 m x 30 m, the AirMAP tropospheric NO2 vertical column density (VCD) data creates a link between the ground-based and the TROPOMI measurements with a resolution of 3.5 km x 5.5 km and is therefore well suited to validate the TROPOMI tropospheric NO2 VCD. The measurements on the seven flight days show strong NO2 variability, which is dependent on the different target areas, the weekday, and the meteorological conditions. The AirMAP campaign dataset is compared to the TROPOMI NO2 operational off-line (OFFL) V01.03.02 data product, the reprocessed NO2 data, using the V02.03.01 of the official L2 processor, provided by the Product Algorithm Laboratory (PAL), and several scientific TROPOMI NO2 data products. The TROPOMI data products and the AirMAP data are highly correlated with correlation coefficients between 0.72 and 0.87, and slopes of 0.38 &plusmn; 0.02 to 1.02 &plusmn; 0.07. On average, TROPOMI tropospheric NO2 VCDs are lower than the AirMAP NO2 results. The slope increased from 0.38 &plusmn; 0.02 for the operational OFFL V01.03.02 product to 0.83 &plusmn; 0.06 after the improvements in the retrieval of the PAL V02.03.01 product were implemented. Different auxiliary data, such as spatially higher resolved a priori NO2 vertical profiles, surface reflectivity and the cloud treatment, are investigated using scientific TROPOMI tropospheric NO2 VCD data products to evaluate their impact on the operational TROPOMI NO2 VCD data product. The comparison of the AirMAP campaign dataset to the scientific data products shows that the choice of surface reflectivity data base has a minor impact on the tropospheric NO2 VCD retrieval in the campaign region and season. In comparison, the replacement of the a priori NO2 profile in combination with the improvements in the retrieval of the PAL V02.03.01 product regarding cloud heights has a major impact on the tropospheric NO2 VCD retrieval and increases the slope from 0.88 &plusmn; 0.06 to 1.00 &plusmn; 0.07. This study demonstrates that the underestimation of the TROPOMI tropospheric NO2 VCD product with respect to the validation dataset has been and can be further significantly improved.</p

Intercomparison of NO2, O4, O3 and HCHO slant column measurements by MAX-DOAS and zenith-sky UV¿visible spectrometers during CINDI-2

40 pags., 22 figs., 13 tabs.In September 2016, 36 spectrometers from 24 institutes measured a number of key atmospheric pollutants for a period of 17¿d during the Second Cabauw Intercomparison campaign for Nitrogen Dioxide measuring Instruments (CINDI-2) that took place at Cabauw, the Netherlands (51.97¿¿N, 4.93¿¿E). We report on the outcome of the formal semi-blind intercomparison exercise, which was held under the umbrella of the Network for the Detection of Atmospheric Composition Change (NDACC) and the European Space Agency (ESA). The three major goals of CINDI-2 were (1) to characterise and better understand the differences between a large number of multi-axis differential optical absorption spectroscopy (MAX-DOAS) and zenith-sky DOAS instruments and analysis methods, (2) to define a robust methodology for performance assessment of all participating instruments, and (3) to contribute to a harmonisation of the measurement settings and retrieval methods. This, in turn, creates the capability to produce consistent high-quality ground-based data sets, which are an essential requirement to generate reliable long-term measurement time series suitable for trend analysis and satellite data validation. The data products investigated during the semi-blind intercomparison are slant columns of nitrogen dioxide (NO2), the oxygen collision complex (O4) and ozone (O3) measured in the UV and visible wavelength region, formaldehyde (HCHO) in the UV spectral region, and NO2 in an additional (smaller) wavelength range in the visible region. The campaign design and implementation processes are discussed in detail including the measurement protocol, calibration procedures and slant column retrieval settings. Strong emphasis was put on the careful alignment and synchronisation of the measurement systems, resulting in a unique set of measurements made under highly comparable air mass conditions. The CINDI-2 data sets were investigated using a regression analysis of the slant columns measured by each instrument and for each of the target data products. The slope and intercept of the regression analysis respectively quantify the mean systematic bias and offset of the individual data sets against the selected reference (which is obtained from the median of either all data sets or a subset), and the rms error provides an estimate of the measurement noise or dispersion. These three criteria are examined and for each of the parameters and each of the data products, performance thresholds are set and applied to all the measurements. The approach presented here has been developed based on heritage from previous intercomparison exercises. It introduces a quantitative assessment of the consistency between all the participating instruments for the MAX-DOAS and zenith-sky DOAS techniques.CINDI-2 received funding from the Netherlands Space Office (NSO). Funding for this study was provided by ESA through the CINDI-2 (ESA contract no. 4000118533/16/ISbo) and FRM4DOAS (ESA contract no. 4000118181/16/I-EF) projects and partly within the EU 7th Framework Programme QA4ECV project (grant agreement no. 607405). The BOKU MAX-DOAS instrument was funded and the participation of Stefan F. Schreier was supported by the Austrian Science Fund (FWF): I 2296-N29. The participation of the University of Toronto team was supported by the Canadian Space Agency (through the AVATARS project) and the Natural Sciences and Engineering Research Council (through the PAHA project). The instrument was primarily funded by the Canada Foundation for Innovation and is usually operated at the Polar Environment Atmospheric Research Laboratory (PEARL) by the Canadian Network for the Detection of Atmospheric Change (CANDAC). Funding for CISC was provided by the UVAS (“Ultraviolet and Visible Atmospheric Sounder”) projects SEOSAT/INGENIO, ESP2015-71299- R, MINECO-FEDER and UE. The activities of the IUP-Heidelberg were supported by the DFG project RAPSODI (grant no. PL 193/17-1). SAOZ and Mini-SAOZ instruments are supported by the Centre National de la Recherche Scientifique (CNRS) and the Centre National d’Etudes Spatiales (CNES). INTA recognises support from the National funding projects HELADO (CTM2013-41311-P) and AVATAR (CGL2014-55230-R). AMOIAP recognises support from the Russian Science Foundation (grant no. 16-17-10275) and the Russian Foundation for Basic Research (grant nos. 16-05- 01062 and 18-35-00682). Ka L. Chan received transnational access funding from ACTRIS-2 (H2020 grant agreement no. 654109). Rainer Volkamer recognises funding from NASA’s Atmospheric Composition Program (NASA-16-NUP2016-0001) and the US National Science Foundation (award AGS-1620530). Henning Finkenzeller is the recipient of a NASA graduate fellowship. Mihalis Vrekoussis recognises support from the University of Bremen and the DFG Research Center/Cluster of Excellence “The Ocean in the Earth System-MARUM”. Financial support through the University of Bremen Institutional Strategy in the framework of the DFG Excellence Initiative is gratefully appreciated for Anja Schönhardt. Pandora instrument deployment was supported by Luftblick through the ESA Pandonia Project and NASA Pandora Project at the Goddard Space Flight Center under NASA Headquarters’ Tropospheric Composition Program. The article processing charges for this open-access publication were covered by BK Scientific

Development and use of compact instruments for tropospheric investigations based on optical spectroscopy from mobile platforms

This thesis presents the development of four different remote-sensing instruments dedicated to atmospheric research and their use in field campaigns between 2008 and 2012. The instruments are based on uv-visible spectrometers and installed respectively on a scientific aircraft (Safire ATR-42), ultralight aircraft, and cars. One of the instruments is targeted to operate from an Unmanned Aerial Vehicle (UAV). The Differential Optical Absorption Spectroscopy (DOAS) technique is used to quantify the molecular absorption in the spectra of scattered sky light. These absorptions are then interpreted by modeling the radiative transfer in the atmosphere. Depending on the instrument, different information on trace gases and aerosols are retrieved: vertical distributions, tropospheric columns, or maps of surface abundances. Airborne platforms enable new measurement geometries, leading for instance to a high sensitivity in the free troposphere. On the other hand, a miniaturization effort is required, especially for the instruments on board ultralight aircraft and UAV. Reaching the limited size, weight, and power consumption is possible through the use of compact spectrometers and computers, together with custom built electronics circuits and housings. The inversion strategies are optimized for each instrument with proper error budgets and the results are compared with other datasets when available. In April 2008, the Airborne Limb Scanning DOAS (ALS-DOAS) was first used on the ATR-42 to derive NO2 and aerosol extinction profiles during the POLar study using Aircraft, Remote sensing, surface measurements and models, of Climate chemistry, Aerosols and Transport (POLARCAT). It revealed in particular that NO2, despite its typical lifetime of a few hours, may be transported from mid-latitude Europe to the Arctic. This is not visible in satellite data since the involved concentrations are under the detection limit. The Ultralight Motorized-DOAS (ULM-DOAS) was operated during the Earth Challenge expedition in April, October, and December 2009. This expedition provided an opportunity to perform measurements from an ultralight between Australia and Belgium, crossing areas were few local measurements have been reported, such as Bangladesh, Rajasthan, Saudi Arabia, and Libya. The ULM-DOAS measurements of tropospheric NO2 columns mostly fall within the confidence interval of satellite data but indicate that the NO2 columns over Riyadh may be underestimated by the Ozone Monitoring Instrument (OMI). In addition, the ULM-DOAS data provided a confirmation for the recent finding of a soil signature in the spectra recorded above desert. The Mobile-DOAS, operated from a car, was developed and first operated during the Cabauw Intercomparison Campaign of Nitrogen Dioxide measuring Instruments (CINDI) in the Netherlands during June and July 2009. Routine measurements in 2010 and 2011, mostly across Belgium yielded a large database of measurements which was compared with a chemical transport model (CHIMERE). The geometric approximation was not used to evaluate the database, since air mass factors calculations indicate that the associated uncertainties are larger than expected from previous studies. Finally, the UAV payload, the Small Whiskbroom Imager for trace gases monitoriNG (SWING) was tested from an ultralight aircraft in July and October 2012. One major objective of the UAV measurements is the mapping of NO2 columns at high spatial resolution allowing to subsample satellite measurements within the extent of a typical ground pixel. This has yet to be achieved.(PHYS 3) -- UCL, 201

Télédétection de la pollution en dioxyde d'azote et en formaldéhyde dans l'atmosphère de Kinshasa à partir d'une station de mesure des polluants atmosphériques

National audienceWe present in this article the fruit of a collaborative effort between the University of Kinshasa through the Department of Physics of the Faculty of Sciences and the UV-Visible group of the Royal Belgian Institute for Space Aeronomy (BIRA-IASB). This collaboration in its first phase resulted in the installation of an optical remote sensing instrument for measuring air pollutants in the Kinshasa atmosphere. Kinshasa, the capital of the Democratic Republic of Congo "DRC", the third largest city in Africa with about 10 million inhabitants, is the source of significant emissions from various pollutants. In this study, we use a remote sensing instrument to measure the abundance of two important gaseous pollutants: dioxide (NO2) and formaldehyde (H2CO) present in the Kinshasa atmosphere. The deployed equipment is based on a commercial grating spectrometer covering the spectral range from 290 to 450 nm, and connected by an optical fiber to record the sky light. A GPS system is integrated into the instrument, allowing for mobile measurements from a vehicle. The control of all the interconnected modules is ensured by a computer running Windows. The different measurements made by the equipment are analyzed and processed by the DOAS "Differential Optical Absorption Spectroscopy" technique. Since the installation of this station in May 2017, we have been able to build a database of several months of measurements that we use to look for trace gas concentrations. Results are analysed for tropospheric NO2 and H2CO signals as well as for stratospheric NO2, the latter being identified in twilight measurements. The system is also shown to allow for stratospheric ozone detection.Nous présentons dans cet article le fruit d’une collaboration entre l’Université de Kinshasa à travers le Département de physique de la Faculté des sciences et le groupe UV-Visible de l’Institut Royal d’Aéronomie Spatiale de Belgique (BIRA-IASB). Cette collaboration dans sa première phase a abouti à l’installation d’un instrument optique de télédétection pour mesurer les polluants atmosphériques dans l’atmosphère de Kinshasa. Kinshasa, la capitale de la République démocratique du Congo "La RDC", troisième ville d’Afrique avec environ 10 millions d’habitants, est à l’origine de nombreuses émissions de polluants. Dans cette étude, nous utilisons un instrument de télédétection pour mesurer l'abondance de deux polluants gazeux importants: le dioxyde (NO2) et le formaldéhyde (H2CO) présents dans l'atmosphère de Kinshasa. L'équipement déployé est basé sur un spectromètre à réseau commercial couvrant la gamme spectrale de 290 à 450 nm, et connecté par une fibre optique pour enregistrer la lumière du ciel. Un système GPS est intégré à l'instrument, permettant des mesures mobiles à partir d'un véhicule. Le contrôle de tous les modules interconnectés est assuré par un ordinateur fonctionnant sous Windows. Les différentes mesures effectuées par les équipements sont analysées et traitées par la technique DOAS "Spectroscopie d'absorption optique différentielle". Depuis l'installation de cette station en mai 2017, nous avons pu constituer une base de données de plusieurs mois de mesures que nous utilisons pour rechercher des concentrations des gaz en traces. Les résultats sont analysés pour les signaux troposphériques de NO2 et de H2CO ainsi que pour les signaux stratosphériques de NO2, ce dernier étant identifié dans les mesures de crépuscule. Le système permet également de détecter l’ozone stratosphérique

Evolution of SO2 and NOx Emissions from Several Large Combustion Plants in Europe during 2005–2015

The aim of this paper is to investigate the evolution of SO2 and NOx emissions of ten very large combustion plants (LCPs &gt;500 MW) located in the European Union (EU) during 2005&ndash;2015. The evolution of NOx and SO2 emissions were analyzed against the EU Directives in force during 2005&ndash;2015. The investigation was performed using space-borne observations and estimated emissions collected from the EEA (European Environment Agency) inventory of air pollutant emissions. The power plants were chosen according to their capacity and emissions, located in various parts of Europe, to give an overall picture of atmospheric pollution with NOx and SO2 associated with the activity of very large LCPs in Europe. Satellite observations from OMI (Ozone Monitoring Instrument) are compared with calculated emissions in order to assess whether satellite observations can be used to monitor air quality, as a standard procedure, by governmental or nongovernmental institutions. Our results show that both space observations and estimated emissions of NOx and SO2 atmospheric content have a descending trend until 2010, complying with the EU Directives. The financial and economic crisis during 2007&ndash;2009 played an important role in reducing emissions