Aircraft-based in situ measurements of CH4 and CO2 downstream of European and Asian urban centres at local to synoptic scales

Die zwei wichtigsten anthropogenen Treibhausgase (THG) sind Kohlenstoffdioxid (CO2) und Methan (CH4), mit globalen Konzentrationen von zurzeit ~414,5 ppm bzw. ~1897 ppb. Zur Begrenzung der globalen Erwärmung ist ein genaues Verständnis ihrer Quellen und Senken erforderlich. Städtische Gebiete sind relevante THG Emittenten, aber aufgrund ihrer vielen individuellen kleinen Quellen sind die gesamten städtischen CO2 und CH4 Emissionen, deren Aufteilung in einzelne Quellsektoren und deren räumliche Verteilung unzureichend bekannt. In dieser Arbeit wird die Hypothese evaluiert, dass flugzeuggestützte in-situ Messungen geeignet sind, um die Auswirkungen urbaner CO2 und CH4 Emissionen auf die lokale bis synoptische THG Verteilung zu identifizieren und zu quantifizieren. Eine hoch empfindliche laser-gestützten Absorptionstechnik (Cavity Ring-Down Spektroskopie) wurde bei drei wissenschaftlichen Messkampagnen eingesetzt: [UC]2 (Urban Climate Under Change), EMeRGe-Europa und EMeRGe-Asien (Effect of Megacities on the transport and transformation of pollutants on the Regional to Global scales). Aufgrund der umfangreichen Charakterisierung des Instruments sowie der Verwendung von Kalibrationsstandards, welche auf die WMO Skala rückführbar sind, beläuft sich die Gesamtunsicherheit der CO2 und CH4 Messungen auf 0,2 ppm bzw. 1,1 ppb (~1 % der atmosphärischen Mischungsverhältnisse). Anhand einer lokalen Fallstudie am 20. Juli während [UC]2 wurde die Berliner THG Fahne vom atmosphärischen Hintergrund abgegrenzt und Emissionsraten für CH4 (5,20 ± 1,70 kg s-1) und CO2 (1,39 ± 0,76 t s-1) mit Hilfe einer Massenbilanz-Methode abgeleitet. Während die extrapolierten jährlichen CO2 Emissionsraten innerhalb der Fehlergrenzen mit aktuellen Emissionskatastern übereinstimmen, liegen sie für CH4 zwei bis siebenmal höher. Der Grund für die Diskrepanz wurde mithilfe von Ergebnissen eines hochauflösenden regionalen Chemie-Klimamodells auf eine Unterschätzung der CH4 Emissionen innerhalb der Stadt, sowie auf fehlende Inventarquellen im Umland zurückgeführt. Für letzteres könnten zahlreiche Mülldeponien und/oder Kläranlagen verantwortlich sein. Diese Arbeit zeigt erfolgreich, dass unabhängige top-down Schätzungen wichtig sind um bottom-up Emissionsraten zu überprüfen. Signaturen von europäischen und asiatischen urbanen CO2 und CH4 Emissionen konnten während EMeRGe im Abwind von London (UK), Barcelona (Spanien) und Manila (Philippinen) detektiert werden. Da die Messentfernung zu den jeweiligen Städten bis zu 250 km betrug, und sich somit die Abluftfahnen bereits mit der Umgebungsluft vermischten, wurde ihre Herkunft mit numerischen Modellsimulationen und zeitgleichen Messungen von kurzlebigen Spurengasen verifiziert. Die Beobachtung von großräumigen CH4 und CO2 Erhöhungen in der freien Troposphäre deuten darauf hin, dass das regionale THG Budget im Frühjahr stark durch den Einfluss vermischter Emissionen von Clustern von Megastädten des chinesischen Festlandes bestimmt wird. Frühere Messkampagnen in Asien (TRACE-P und KORUS-AQ der NASA) weisen ähnliche Muster in der regionalen THG Verteilung auf. Wie erwartet wurden jedoch höhere mittlere Mischungsverhältnisse während EMeRGe-Asien aufgrund der globalen Zunahme atmosphärischer CO2 und CH4 Konzentrationen detektiert. Diese Arbeiten bestätigen, dass in-situ Messungen ebenso erfolgreich eingesetzt werden können, um städtische THG Emissionen auf der meso- bis synoptischen Skala zu untersuchen.The two most important anthropogenic greenhouse gases (GHG) are carbon dioxide (CO2) and methane (CH4) with current global mole fractions of ~414.5 ppm CO2 and ~1897 ppb CH4. In order to develop efficient mitigation strategies limiting global warming, an accurate understanding of their sources and sinks is necessary. Urban areas are recognised as significant GHG emitters but constitute of a large variety of individual smaller sources. Hence, there is a lack of information on the magnitude of total urban CO2 and CH4 emissions, on their division into different source sectors and on their spatial distribution. This thesis evaluates the hypothesis that aircraft-borne in situ measurements are a useful tool to identify and quantify the impact of urban CH4 and CO2 emissions on the local to synoptic scale GHG distribution. A sensitive laser-based absorption technique, cavity ring-down spectroscopy, was deployed within three scientific field campaigns: [UC]2 (Urban Climate Under Change), EMeRGe-Europe and EMeRGe-Asia (Effect of Megacities on the transport and transformation of pollutants on the Regional to Global scales). The extensive characterisation and calibration with gas standards traceable to the WMO scales allows for measuring CO2 and CH4 mole fractions with an overall uncertainty of 0.2 ppm and 1.1 ppb, respectively, representing less than 1 % of the current atmospheric background. Based on a local case study on July 20th during [UC]2 it was possible to clearly distinguish Berlin’s urban GHG plume from the atmospheric background and to derive emission rates for CH4 (5.20 ± 1.70 kg s-1) and CO2 (1.39 ± 0.76 t s-1) using a mass balance method. While extrapolated annual CO2 emission rates agree within error bars with current inventories, they are two to seven times higher for CH4. Combining aircraft measurements with results from a high-resolution regional chemistry climate model, it was shown that the discrepancy is due to an underestimation of urban CH4 emissions within the city, as well as due to missing inventorial sources in the surroundings, which may include numerous waste dumps and/or wastewater treatment plants. This study successfully demonstrates that such independent airborne top-down estimates are important to evaluate bottom-up emission inventories. Signatures of European and Asian urban CO2 and CH4 emissions were detected in the regional GHG budget during EMeRGe for London (United Kingdom), Barcelona (Spain) and Manila (the Philippines) even at downwind distances up to 250 km. Due to the large distances from the respective sources, emissions were already mixed with cleaner background air or other pollution plumes. Their identification therefore was verified by numerical model simulations and co-measured short-lived species. The frequent observation of large-scale GHG plumes in the free troposphere downstream of China, indicate that the regional GHG budget during springtime is heavily impacted by the outflow from mixed emissions from megacity clusters from mainland China. A comparison with previous aircraft campaigns conducted in Asia (TRACE-P and KORUS-AQ of NASA) shows that similar patterns were observed in the regional GHG distributions. However, as expected, larger mean mole fractions were detected during EMeRGe-Asia due to the increase in global atmospheric CO2 and CH4 concentrations. These studies show that in situ instruments can also be successfully used to study the impact of urban emissions on the meso- to synoptic scale GHG budget

Emissions of sulphur dioxide (SO2) from coal-fired power plants in Serbia and Bosnia-Herzegovina: First attempts of a validation of TROPOMI satellite products with airborne in situ measurements

The Western Balkan region is known for emitting alarmingly high sulphur dioxide amounts from coal-fired power plants. Though a number of environmental regulations have been introduced in recent years (e.g. desulphurisation installations, construction of modern power plants), the pollution burden is still much higher than recommended by the authorities. A number of different montoring systems are required to observe the growing pollution situation in the Western Balkan region, partly caused by a high energy demand from outside (e.g. Western Europe)

Atmospheric Carbon and Transport - America (ACT-America) Data Sets: Description, Management, and Delivery

Abstract The ACT‐America project is a NASA Earth Venture Suborbital‐2 mission designed to study the transport and fluxes of greenhouse gases. The open and freely available ACT‐America data sets provide airborne in situ measurements of atmospheric carbon dioxide, methane, trace gases, aerosols, clouds, and meteorological properties, airborne remote sensing measurements of aerosol backscatter, atmospheric boundary layer height and columnar content of atmospheric carbon dioxide, tower‐based measurements, and modeled atmospheric mole fractions and regional carbon fluxes of greenhouse gases over the Central and Eastern United States. We conducted 121 research flights during five campaigns in four seasons during 2016–2019 over three regions of the US (Mid‐Atlantic, Midwest and South) using two NASA research aircraft (B‐200 and C‐130). We performed three flight patterns (fair weather, frontal crossings, and OCO‐2 underflights) and collected more than 1,140 h of airborne measurements via level‐leg flights in the atmospheric boundary layer, lower, and upper free troposphere and vertical profiles spanning these altitudes. We also merged various airborne in situ measurements onto a common standard sampling interval, which brings coherence to the data, creates geolocated data products, and makes it much easier for the users to perform holistic analysis of the ACT‐America data products. Here, we report on detailed information of data sets collected, the workflow for data sets including storage and processing of the quality controlled and quality assured harmonized observations, and their archival and formatting for users. Finally, we provide some important information on the dissemination of data products including metadata and highlights of applications of ACT‐America data sets

Potential vorticity diagnostics based on balances between volume integral and boundary conditions

International audienceTaking advantage of alternative expressions for potential vorticity (PV) in divergence forms, we derive balances between volume integral of PV and boundary conditions, that are then applied to practical computations of PV: • we propose a new method for diagnosing the Ertel potential vorticity from model output, that preserves the balances; • we show how the expression of PV can be derived in general coordinate systems. This is here emphasised with isopycnic coordinates by generalising the PV expression to the general Navier-Stokes equations; • we propose a generalised derivation for the Haynes-McIntyre imper- meability theorem, which highlights the role of the bottom boundary condition choice (e.g. no-slip vs free-slip) and mixing near the bottom boundary for the volume integral of PV. The implications of balances between volume integral of PV and boundary conditions are then analysed for specific processes at various scales: • at large scale, we show how an integral involving surface observations (derived from satellite observations) is linked to the integral of PV within a layer (between two isopycnals). This surface integral can be calculated for models and observations and can be used for validation; • at mesoscale or sub-mesoscale, we analyse the relationship between net PV anomalies and net surface density anomalies for idealised vortices and 2D fronts. This can help determining vortex or jet structures for idealised studies or empirical methodologies; • we also confirm and integrate previous results on the modification of PV within a bottom boundary layer into a single diagnostic taking into account the effect of density and velocity modifications by diabatic processes along the topography and diapycnal mixing within the boundary layer