Nitrogen dioxide (NO2) and nitrogen oxide (NO), usually referred to as nitrogen oxides (NOx), are emitted into the atmosphere by anthropogenic and natural sources. The detection and monitoring of NO2 plays a key role in air quality managements because of its effects on health and of its contribution to the increase of tropospheric ozone and nitrate aerosols. Unfortunately, up to now, observations were possible only once a day based on satellites in low-earth orbit (GOME, GOME-2, OMI and TROPOMI). However, from now on, it is possible to observe the diurnal variations over the Asia based on Geostationary Environment Monitoring Spectrometer (GEMS) in geostationary earth orbit. Here, we present results of tropospheric nitrogen dioxide column observations with high temporal (hourly) and spatial resolutions over major cities in Asia. In addition, we evaluate the GEMS NO2 operational algorithm by comparing GEMS total and tropospheric NO2 columns with independent observations from ground-based Pandora (total column) and MAX-DOAS (tropospheric column). Additionally, we retrieved the GEMS tropospheric NO2 columns by subtracting the stratospheric NO2 columns, which are assumed based on SLIMCAT model data and then scalded with the real GEMS observations, from the total NO2 columns. Then we also compared the tropospheric NO2 columns that are retrieved based on GEMS NO2 operational algorithm and SLIMCAT model, respectively. Lastly, we compared the GEMS NO2 with other low-earth orbit satellite instruments that include OMI and TROPOMI.

Conventional spectroscopic methods have proven to be reliable and of high selectivity by utilizing the characteristic spectral absorption signature of a wide range of atmospheric trace gases, such as NO2. However, they typically lack the spatio-temporal resolution required to resolve fast processes, such as NO2 emissions from stacks or other point sources. We present a novel fast imaging instrument for NO2: the NO2 camera based on Gas Correlation Spectroscopy (GCS) in the blue spectral range. Two gas cells (cuvettes) are placed in front of two camera modules. One gas cell is empty, while the other is filled with a high concentration of the target gas (i.e. NO2). The filled gas cell operates as a non-dispersive spectral filter to the incoming light, maintaining the two-dimensional imaging capability of the sensor arrays. NO2 images are generated on the basis of the light intensity ratio between the two images in the spectral window between 430 and 445 nm, where the NO2 absorption cross section has strong spectral structures. We report measurements taken at a large power plant, the Großkraftwerk Mannheim (GKM) in Baden-Württemberg, Germany. NO2 column densities in the stack plume of a GKM chimney are quantified at a spatio-temporal resolution of 1/12 frames per second (FPS) and 0.92m x 0.92m. A detection limit of 2·1016 molec cm-2 was reached. An NO2 mass flux of (7.4 ± 4.2) kg h-1 was estimated based on momentary wind speeds obtained from consecutive images using optical flow estimation. By comparison with a well-established model for plume chemistry (Janssen model), we demonstrate that the NO2/NOx ratio of stack plumes can be investigated using an imaging instrument like ours. The instrument prototype is highly portable and cost-efficient at building costs of below 2,000 Euro.

European UVN satellite missions deliver global measurements for air quality and climate applications from Low Earth Orbit (LEO) satellites since over two decades. Currently we have in the morning data from GOME-2 on the three MetOp satellites and in the early afternoon data from OMI/Aura and TROPOMI/Sentinel-5 Precursor. The temporal barrier imposed by LEO satellites, providing only one daily observation, can be broken using Geostationary Equatorial Orbit (GEO) satellites. The Sentinel-4 (S4) mission on-board the MTG-S GEO satellite will focus on monitoring of trace gas column densities and aerosols over Europe with an hourly revisit time, thereby covering the diurnal variation of atmospheric constituents. We present the algorithm, verification, and processor work being performed as part of the ESA Sentinel-4 Level 2 (S4-L2) project responsible for developing the operational S4-L2 products: O3 total and tropospheric column, NO2 total and tropospheric column, SO2, HCHO, CHOCHO columns, aerosol and cloud properties as well as surface reflectance.

The aerosol index (AER_AI) as calculated using data from the Tropospheric Monitoring Instrument (TROPOMI) onboard the ESA Sentinel 5 Precursor (S5P) platform was publically released in July 2018. The operational AER_AI dataset is available from May 2018 through the present. It is a useful data product not only for tracking ultraviolet (UV) absorbing aerosol plumes of desert dust, volcanic ash, and smoke from biomass burning but also for monitoring the quality of the TROPOMI Level 1b (L1b) data since the AER_AI calculation is very sensitive to the absolute calibration of irradiance and radiance. The aim of this work is first to highlight the new level of detail seen in aerosol plume events based on the recent switch to a reduced pixel size of 3.5 x 5.5 km. Such high spatial resolution also presents specific challenges as non-Lambertian cloud features and 3-D effects of clouds are now visible in the TROPOMI AER_AI data. Plans for an approach to flag and correct these features in future AER_AI updates will be given. Secondly this work will include an overview of the impacts on AER_AI due to observed degradation in the TROPOMI measured irradiance and wavelength-dependent features in the radiance. As a result of these L1b effects, there is a steadily increasing negative bias in the global mean AER_AI value. Examples are given how the new version of the L1b data (2.0.0) will be used to correct for this degradation-driven bias. Recommendations are also given to guide data users looking to perform trend analysis or those using AER_AI as a filter for aerosol removal or detection in other L2 data products.

The growth of ultrathin Cr overlayers on SrTiO3(100) was studied by X-ray photoelectron spectroscopy, scanning tunneling microscopy, and transmission electron microscopy. It is found that the metal–oxide interaction strongly depends on the deposition temperature. At T<600°C, the interfaces are atomically sharp. Local charge transfer happens between the interfacial Cr adatoms and the topmost substrate atoms. The binding energy shift of Cr 2p is dominated by the final state effects. In case of T>600°C, bulk diffusion of oxygen in the oxide substrate may occur, which results in a redox reaction and the formation of new reaction phases at the interfaces. In this temperature regime, the binding energy shift of Cr 2p is mainly controlled by the initial state effects.

The model system Cr/SrTiO3 was used to show how interfacial reactions can be tuned over a temperature range of several hundred Kelvin by a distinct modification of the electronic structure in the oxide. This mechanism unveils the dominant role of the Fermi energy level (EF) in the oxide’s band gap for interfacial reactions and can be understood by the interplay between the outward diffusion of oxygen ions and space charges formed at the Cr/SrTiO3 interfaces. The results suggest that the interfacial reactivity is tunable by modifying EF in the oxide, which will be decisive for present and future applications in the fields of sensors, catalysis and microelectronics.

The model system Pd/TiO2 (110) was used to evaluate the correlation between metal encapsulation and electronic structure of TiO2 crystals. We observed encapsulation of Pd clusters supported on TiO2 crystals, which were heavily Ar+ sputtered, Nb-doped, or reduced by vacuum annealing. In contrast, encapsulation was not observed on unreduced, undoped, or slightly sputtered TiO2 crystals. Our results indicate a strong dependence of the encapsulation process on the electron density in the conduction band of TiO2 and on the space charge formed at Pd/TiO2 interfaces. This behavior is controlled by the initial position of the Fermi energy level (EF) of the metal and the oxide before contact is established. We proved that encapsulation reactions are favored by n-type doping of the oxide and a large work function of the metal. On the basis of this mechanism, we conclude on general trends controlling encapsulation reactions of oxide-supported metal clusters and the strong metal-support interaction (SMSI).

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

Grain growth and texture development of magnetron-sputtered Ni films on thermally oxidized Si wafers were investigated as a function of sputtering and annealing atmospheres. Ni films of 1 mum thickness were sputtered in either pure Ar or an Ar-H-2 gas mixture and subsequently annealed in high vacuum or a hydrogen atmosphere at 800 degreesC. The films were characterized by focused ion-beam microscopy and X-ray diffraction. The Ni films had a strong {111} texture after sputtering. Films sputtered in an Ar-H-2 mixture and annealed in H-2 underwent abnormal grain growth, resulting in a {100} texture. These films had a mean grain diameter of about 50 mum. The unusual abnormal grain growth is believed to be caused by a cleaning of the Ni films during sputtering and annealing in H-2.

The effect of low-energy ion bombardment on the microstructure of copper films will be described. The copper films have been deposited on SiNx-coated, oxidized Si wafers by magnetron sputtering with a simultaneous bombardment of low-energy argon ions (60 eV). The films were annealed at 450°C in HV. The ion bombardment leads to a stronger and sharper {111} texture of the as-deposited films. After annealing, the ion-bombarded films had a significantly smaller grain size than films produced without ion bombardment. The experimental results will be discussed relating the textures of the as-deposited films with the grain sizes obtained after annealing. Details will be given describing how the microstructure of Cu films can be tailored using low-energy argon ion bombardment.

Atomic force microscopy (AFM) was used to characterize the surface morphology of (100) SrTiO3 single-crystal substrates. The crystals were annealed at 1100°C in O2 for up to 3 h. Successive AFM imaging of identical regions on the SrTiO3 surfaces was carried out before and after wet chemical etching and throughout a series of heat treatments. Differences in surface morphology between etched and unetched crystals were observed and are attributed to the removal of surface impurities during the etching process. Auger electron spectroscopy shows widespread calcium contamination on as-received, commercially-prepared substrates. Zeta-potential measurements suggest that Ca2+ ions adsorb to the surface of SrTiO3 in alkaline solutions.

The Nb/α−Al_2O_3 system has been used as a model study for investigating the stability of different MBE grown epitaxial Nb films on α−Al_2O_3 substrates. The films were grown at 800 °C in ultrahigh vacuum. The growth process was monitored in situ by reflection high energy electron diffraction (RHEED). After deposition the structure of the film was investigated by x-ray diffraction (XRD) and conventional transmission electron microscopy (CTEM) which encompasses also selected area diffraction (SAD). Both techniques revealed the following orientation relationship between the Nb film and the α–Al_2O_3 substrate: (0001)α–Al_2O_3‖ (111)Nb; [2110]α–Al_2O_3‖ [110]Nb. The stability of the niobium films was investigated by annealing the Nb-film/α–Al_2O_3 system to temperatures up to 1500 °C for different periods of time. Surprisingly, the orientation relationship between the Nb film and the substrate changed to (0001)α–Al_2O_3‖ (110)Nb; [0110]α–Al_2O_3‖ [001]Nb. A model will be developed which shows that above a critical film thickness the growth orientation is metastable with respect to its crystallographic orientation. Furthermore, high resolution transmission electron microscopy (HREM) was performed to investigate the defect structure of the annealed Nb/α–Al_2O_3 interface.