53 research outputs found
Developing an Aerosol Layer Height Retrieval Algorithm for Passive Space-Based Sensors
No full textAerosols are the source of the largest uncertainties in our climate models, blurring our outlook of the future. This has been attributed to the complexity of measuring their properties, which vary over time and space. Atmospheric circulation spreads aerosols across the globe from a point source, which makes satellite-based observations lucrative. At present, there are several aerosol observing missions that deliver aerosol data products in a consistent and operational manner; these missions report several aerosol properties that are important for reducing the contribution of uncertainties to our climate models. What is missing, however, is an operational data product that measures the height of these aerosols at a global scale. Earlier attempts at this use data derived from lidar instruments in space; an example being the Cloud-Aerosol Lidar with Orthogonal Polarisation (CALIOP) instrument, which uses lasers to measure atmospheric composition. In the case of aerosols, the amount of backscattered electromagnetic radiation at each atmospheric layer gives an idea of the amount and height of aerosols. The mobility afforded by space-based instruments gives space lidars a leg up over ground-based lidars. However, the coverage of such lidar instruments is merely near-global. This has to do with the fact that while lidars in space can circle the entire globe, their footprint on the ground is very narrow, in the order of several hundred meters to a few kilometers: this is an inherent limitation of the measurement principle. Consequently, a specific patch on Earth is revisited in periods that can range several days. An alternative to space based atmospheric lidars are space based spectral imagers. These are essentially cameras that take snapshots of the Earth, capturing the light and splitting its different electromagnetic frequencies into the scale of nanometers using very precise prisms and detection techniques. The advantage of these instruments over lidars is that they have a very large footprint, covering several thousand kilometers of area in a single _y-by. This allows for daily to even sub-daily coverage of the Earth, as each snapshot covers larger and sometimes overlapping areas. The challenge is to estimate aerosol height using spectral signatures of the Earth’s atmosphere in an operational environment that can handle data coming in from the satellite at a rate of several million pixels every few minutes. This dissertation focuses on delivering the aerosol height data product operationally using computer algorithms. The logic of aerosol height estimation using these so-called spectral snapshots of the atmosphere differ from that using lidars; the instrument does not provide data for different atmospheric layers. This has to be inferred using the chemistry of the oxygen molecule. O2, the second most abundant gas in our atmosphere, has a unique spectral signature in the near-infrared region, comprising of electromagnetic radiation around 765 nm. The chemical structure of the oxygen molecule allows it to absorb some of these radiations, creating a structure of absorption bands. This spectral signature deepens as more light is absorbed by the oxygen: this happens as photons penetrate deeper and deeper into the earth’s atmosphere, unless they hit a barrier. If the photons bounce back from an aerosol layer at a very high altitude, the amount of absorption by oxygen would be low. This ‘depth’ of absorption gives clues on how high an aerosol layer might be present. Computer models can reconstruct this oxygen absorption structure onto a simulated spectrum. One of the control parameters within the model is the height of an aerosol layer. The generated spectral signature of a simulated atmosphere resembling the atmosphere of a pixel in the snapshot from space-based hyperspectral imagers is then compared to the measured spectral signature. This usually results in a non-zero difference, which is caused by errors in the model. These errors can be minimised by using computer algorithms and mathematical information retrieval techniques, resulting in a modeled atmosphere closer to the measurement by changing the height of the aerosol layer, resulting in an aerosol height estimate. In this dissertation, computer algorithms inspired from mathematical models of brain neural networks as well as information retrieval techniques such as least squares are used…Atmospheric Remote Sensin
The role of aerosol layer height in quantifying aerosol absorption from ultraviolet satellite observations
No full textThe purpose of this study is to demonstrate the role of aerosol layer height (ALH) in quantifying the single scattering albedo (SSA) from ultraviolet satellite observations for biomass burning aerosols. In the first experiment, we retrieve SSA by minimizing the near-ultraviolet (near-UV) absorbing aerosol index (UVAI) difference between observed values and those simulated by a radiative transfer model. With the recently released S-5P TROPOMI ALH product constraining forward simulations, a significant gap in the retrieved SSA (0.25) is found between radiative transfer simulations with spectral flat aerosols and those with strong spectrally dependent aerosols, implying that inappropriate assumptions regarding aerosol absorption spectral dependence may cause severe misinterpretations of the aerosol absorption. In the second part of this paper, we propose an alternative method to retrieve SSA based on a long-term record of co-located satellite and ground-based measurements using the support vector regression (SVR) approach. This empirical method is free from the uncertainties due to the imperfection of a priori assumptions on aerosol microphysics seen in the first experiment. We present the potential capabilities of SVR using several fire events that have occurred in recent years. For all cases, the difference between SVR-retrieved SSA and AERONET are generally within ±0:05, and over half of the samples are within ±0:03. The results are encouraging, although in the current phase the model tends to overestimate the SSA for relatively absorbing cases and fails to predict SSA for some extreme situations. The spatial contrast in SSA retrieved by radiative transfer simulations is significantly higher than that retrieved by SVR, and the latter better agrees with SSA from MERRA-2 reanalysis. In the future, more sophisticated feature selection procedures and kernel functions should be taken into consideration to improve the SVR model accuracy. Moreover, the high-resolution TROPOMI UVAI and co-located ALH products will guide us to more reliable training data sets and more powerful algorithms to quantify aerosol absorption from UVAI records.Atmospheric Remote Sensin
Prevalence of Leber hereditary optic neuropathy in the Community of Madrid (Spain), estimation with a capture-recapture method
No full textPublisher Copyright: © The Author(s) 2024.Peer reviewe
S-5P/TROPOMI-Derived NO<sub>x</sub> Emissions From Copper/Cobalt Mining and Other Industrial Activities in the Copperbelt (Democratic Republic of Congo and Zambia)
No full textWe have analyzed Sentinel-5 Precursor TROPOspheric Monitoring Instrument (TROPOMI) data over the Copperbelt mining region (Democratic Republic of Congo and Zambia). Despite high background values, annual 2019–2022 means of TROPOMI NO2 (nitrogen dioxide) show local enhancements consistent with six point sources (four copper/cobalt mines, two cities) where high-emission industrial activities take place. We have quantified annual NOx (nitrogen oxides) emissions from these point sources, identified temporal trends in emissions, and found strong correlations with production data from colocated mines and one oil refinery. The Copernicus Atmosphere Monitoring Service Global Anthropogenic (CAMS-GLOB-ANT) version 5 inventory underpredicts TROPOMI-derived emissions and lacks the temporal trends observed in TROPOMI and mine/refinery production. These results demonstrate the potential for satellite monitoring of mining and other industrial activities, often unreported or underestimated, which impact the air quality of local communities. This is particularly important for Africa, where mining is increasing aggressively.Atmospheric Remote Sensin
Petonii Curiosa Felicitas: La función de las citas en el discurso de Eumolpo (Sat. 118)
No full textEste trabajo analiza el fenómeno intertextual de la ?cita? en Petronio, Sat. 118, donde el poeta de la obra, Eumolpo, expone su particular ?ars poetica?. En este discurso, Eumolpo cita los nombres de Homero, Virgilio y Horacio, al tiempo que cita el primer verso de la Oda 3.1 del Venusino, lo que evidencia que el poetastro tiene muy en cuenta la figura horaciana. El análisis de las citas en este pasaje se relaciona con que Petronio es un autor que alude constantemente, pero que cita muy rara vez, por lo que, cuando lo hace, se debe prestar mucha atenciónThis paper surveys the intertextual phenomenon of `quotation' in Petronius, Sat. 118, where the poet, Eumolpus, sets out his particular 'ars poetica'. In this speech, Eumolpus quotes the names of Homer, Virgil and Horace, along with Horace?s Carm. 3.1.1, which demonstrates that the poetaster bears in mind the Venusian author. The survey of the quotations in this passage is related to the fact that Petronius is an author who constantly alludes but rarely quotes, so that when he does it, the reader should pay close attentionFil: Carmignani, Andrés. Universidad Nacional de Córdoba; CONICET
Sources of Formaldehyde in U.S. Oil and Gas Production Regions
No full textWe analyzed observational and model data to study the sources of formaldehyde over oil and gas production regions and to investigate how these observations may be used to constrain oil and gas volatile organic compound (VOC) emissions. The analysis of aircraft and satellite data consistently found that formaldehyde over oil and gas production regions during spring and summer is mostly formed by the photooxidation of precursor VOCs. Formaldehyde columns over the Permian Basin, one of the largest oil- and gas-producing regions in the United States, are correlated with the production locations. Formaldehyde simulations by the atmospheric chemistry and transport model WRF-Chem, which included oil and gas NOx and VOC emissions from the fuel-based oil and gas inventory, were in very good agreement with TROPOMI satellite measurements. Sensitivity studies illustrated that VOCs released from oil and gas activities are important precursors to formaldehyde, but other sources of VOCs contribute as well and that the formation of secondary formaldehyde is highly sensitive to NOx. We also investigated the ability of the chemical mechanism used in WRF-Chem to represent formaldehyde formation from oil and gas hydrocarbons by comparing against the Master Chemical Mechanism. Further, our work provides estimates of primary formaldehyde emissions from oil and gas production activities, with per basin averages ranging from 0.07 to 2.2 kg h-1 in 2018. A separate estimate for natural gas flaring found that flaring emissions could contribute 5 to 12% to the total primary formaldehyde emissions for the Permian Basin in 2018.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Control & SimulationAtmospheric Remote Sensin
Application of the Multi-Scale Infrastructure for Chemistry and Aerosols version 0 (MUSICAv0) for air quality research in Africa
No full textThe Multi-Scale Infrastructure for Chemistry and Aerosols Version 0 (MUSICAv0) is a new community modeling infrastructure that enables the study of atmospheric composition and chemistry across all relevant scales. We develop a MUSICAv0 grid with Africa refinement (∼ 28 km × 28 km over Africa). We evaluate the MUSICAv0 simulation for 2017 with in situ observations and compare the model results to satellite products over Africa. A simulation from the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem), a regional model that is widely used in Africa studies, is also included in the analyses as a reference. Overall, the performance of MUSICAv0 is comparable to WRF-Chem. Both models underestimate carbon monoxide (CO) compared to in situ observations and satellite CO column retrievals from the Measurements of Pollution in the Troposphere (MOPITT) satellite instrument. MUSICAv0 tends to overestimate ozone (O3), likely due to overestimated stratosphere-to-troposphere flux of ozone. Both models significantly underestimate fine particulate matter (PM2.5) at two surface sites in East Africa. The MUSICAv0 simulation agrees better with aerosol optical depth (AOD) retrievals from the Moderate Resolution Imaging Spectroradiometer (MODIS) and tropospheric nitrogen dioxide (NO2) column retrievals from the Ozone Monitoring Instrument (OMI) than WRF-Chem. MUSICAv0 has a consistently lower tropospheric formaldehyde (HCHO) column than OMI retrievals. Based on model–satellite discrepancies between MUSICAv0 and WRF-Chem and MOPITT CO, MODIS AOD, and OMI tropospheric NO2, we find that future field campaign(s) and more in situ observations in the East African region (5∘ S–5∘ N, 30–45∘ E) could substantially improve the predictive skill of atmospheric chemistry model(s). This suggested focus region exhibits the largest model–in situ observation discrepancies, as well as targets for high population density, land cover variability, and anthropogenic pollution sources.Atmospheric Remote Sensin
Petonii Curiosa Felicitas: La función de las citas en el discurso de Eumolpo [Sat. 118]
No full textThis paper surveys the intertextual phenomenon of `quotation' in Petronius, Sat. 118, where the poet, Eumolpus, sets out his particular 'ars poetica'. In this speech, Eumolpus quotes the names of Homer, Virgil and Horace, along with Horace?s Carm. 3.1.1, which demonstrates that the poetaster bears in mind the Venusian author. The survey of the quotations in this passage is related to the fact that Petronius is an author who constantly alludes but rarely quotes, so that when he does it, the reader should pay close attentionEste trabajo analiza el fenómeno intertextual de la ?cita? en Petronio, Sat. 118, donde el poeta de la obra, Eumolpo, expone su particular ?ars poetica?. En este discurso, Eumolpo cita los nombres de Homero, Virgilio y Horacio, al tiempo que cita el primer verso de la Oda 3.1 del Venusino, lo que evidencia que el poetastro tiene muy en cuenta la figura horaciana. El análisis de las citas en este pasaje se relaciona con que Petronio es un autor que alude constantemente, pero que cita muy rara vez, por lo que, cuando lo hace, se debe prestar mucha atenció
The case for a symmetric reaction function of the European Central Bank
No full textIn a macro-economic framework where the European Central Bank targets individual country data, the nature of strategic interactions between fiscal authorities in the euro-zone can be described as a stag hunt game with (at least) two equilibria that can be pareto-ranked. In fact we show that, because of the indiscriminate nature of its monetary response, an ECB strategy of monetary retaliation to any individual countrys over-expenditure affects all eleven countries to the same extent. This collective effect is similar to the teachers old favorite all children stay behind in the class if one misbehaves. This mechanism, we show, makes the game between fiscal authorities a multiple equilibria co-ordination game. We subsequently address the problem of equilibrium selection that is of particular importance to co-ordination games. Following Kandori et al. (1993), we apply Harsanyi and Seltens (1988) riskdominance criterion to single out the conditions for fiscal restraint to emerge as the equilibrium selected by interacting actors. Our main conclusions are that the ECB can ensure convergence of fiscal authorities upon the pareto-optimal equilibrium (that is, fiscal restraint) by adopting a reward-oriented, counter-cyclical strategy that compensates fiscal authorities at the output level both for giving up fiscal discretion and for incurring the risk of being hit by a monetary tightening in response to developments elsewhere in the euro-economy. This means that interest rates' movements should smoothen economic fluctuations in order to give economic actors sufficient incentives to maintain restraint. -- In einem makroökonomischen Kontext, in dem die Europäische Zentralbank die wirtschaftlichen Daten einzelner Länder anvisiert, können die strategischen Interaktionen zwischen den Finanzbehörden der Euro-Zone als ein stag hunt- Spiel mit (mindestens) zwei pareto-Equilibrien beschrieben werden. Wir zeigen daß, aufgrund der ungezielten Art der monetären Reaktion, eine EZB-Strategie der monetären Vergeltung für zu hohe Ausgaben eines einzelnen Landes alle elf Länder gleichermaßen betrifft. Dieser Kollektiveffekt erinnert an die alte Lehrermethode: Alle Kinder müssen nachsitzen, wenn eins aus der Reihe tanzt. Dieser Mechanismus macht das Spiel zwischen den Finanzbehörden zu einem Koordinationsspiel mit mehreren Equilibrien. Anschließend befassen wir uns mit dem in Koordinationsspielen besonders bedeutsamen Problem der Wahl zwischen Equilibrien. In Anlehnung an Kandori et al. (1993) wenden wir Harsanyi und Selten's (1988) Risikodominanzkriterium an, um die Bedingungen herauszufiltern, unter denen fiskale Zurückhaltung das Equilibrium bildet, das von den beteiligten Akteuren gewählt wird. Unsere wesentlichen Schlußfolgerungen sind, daß die EZB eine Konvergenz der Finanzbehörden auf das pareto-optimale Equilibrium (d.h. fiskale Zurückhaltung) sicherstellen kann, indem sie eine auf Belohnung ausgerichte, antizyklische Strategie verfolgt, bei der die Finanzbehörden auf der Output-Ebene entschädigt werden -sowohl für die Abgabe fiskaler Entscheidungsfreiheit als auch für das Risiko, einer monetären Kontraktion ausgesetzt zu werden, die auf Entwicklungen anderswo in der Euro-Wirtschaft abzielt. Das bedeutet, daß Zinsentwicklungen wirtschaftliche Fluktuationen ausgleichen sollten, um den relevanten Akteuren ausreichende Anreize für fiskale Zurückhaltung zu bieten.
A first comparison of TROPOMI aerosol layer height (ALH) to CALIOP data
No full textThe TROPOspheric Monitoring Instrument (TROPOMI) level-2 aerosol layer height (ALH) product has now been released to the general public. This product is retrieved using TROPOMI's measurements of the oxygen A-band, radiative transfer model (RTM) calculations augmented by neural networks and an iterative optimal estimation technique. The TROPOMI ALH product will deliver ALH estimates over cloud-free scenes over the ocean and land that contain aerosols above a certain threshold of the measured UV aerosol index (UVAI) in the ultraviolet region. This paper provides background for the ALH product and explores its quality by comparing ALH estimates to similar quantities derived from spaceborne lidars observing the same scene. The spaceborne lidar chosen for this study is the Cloud-Aerosol LIdar with Orthogonal Polarization (CALIOP) on the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) mission, which flies in formation with NASA's A-train constellation since 2006 and is a proven source of data for studying ALHs. The influence of the surface and clouds is discussed, and the aspects of the TROPOMI ALH algorithm that will require future development efforts are highlighted. A case-by-case analysis of the data from the four selected cases (mostly around the Saharan region with approximately 800 co-located TROPOMI pixels and CALIOP profiles in June and December 2018) shows that ALHs retrieved from TROPOMI using the operational Sentinel-5 Precursor Level-2 ALH algorithm is lower than CALIOP aerosol extinction heights by approximately 0.5km. Looking at data beyond these cases, it is clear that there is a significant difference when it comes to retrievals over land, where these differences can easily go over 1km on average.Atmospheric Remote Sensin
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