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Retrieval of absolute SO<sub>2</sub> column amounts from scattered-light spectra: implications for the evaluation of data from automated DOAS networks
摘要： Scanning spectrometer networks using scattered solar radiation in the ultraviolet spectral region have become an increasingly important tool for monitoring volcanic sulfur dioxide (SO2) emissions. Often measured spectra are evaluated using the differential optical absorption spectroscopy (DOAS) technique. In order to obtain absolute column densities (CDs), the DOAS evaluation requires a Fraunhofer reference spectrum (FRS) that is free of absorption structures of the trace gas of interest. For measurements at volcanoes such a FRS can be readily obtained if the scan (i.e. series of measurements at different elevation angles) includes viewing directions where the plume is not seen. In this case, it is possible to use these viewing directions (e.g. zenith) as FRS. Possible contaminations of the FRS by the plume can then be corrected by calculating and subtracting an SO2 offset (e.g. the lowest SO2 CD) from all viewing directions of the respective scan. This procedure is followed in the standard evaluations of data from the Network for Observation of Volcanic and Atmospheric Change (NOVAC). While this procedure is very efficient in removing Fraunhofer structures and instrumental effects it has the disadvantage that one can never be sure that there is no SO2 from the plume in the FRS. Therefore, using a modelled FRS (based on a high-resolution solar atlas) has a great advantage. We followed this approach and investigated an SO2 retrieval algorithm using a modelled FRS. In this paper, we present results from two volcanoes that are monitored by NOVAC stations and which frequently emit large volcanic plumes: Nevado del Ruiz (Colombia) recorded between January 2010 and June 2012 and from Tungurahua (Ecuador) recorded between January 2009 and December 2011. Instrumental effects were identified with help of a principal component analysis (PCA) of the residual structures of the DOAS evaluation. The SO2 retrieval performed extraordinarily well with an SO2 DOAS retrieval error of 1?2×1016 [molecules cm?2]. Compared to a standard evaluation, we found systematic differences of the differential slant column density (dSCD) of only up to ≈ 15 % when looking at the variation of the SO2 within one scan. The major advantage of our new retrieval is that it yields absolute SO2 CDs and that it does not require complicated instrumental calibration in the field (e.g. by employing calibration cells or broadband light sources), since the method exploits the information available in the measurements.
关键词： Fraunhofer reference spectrum,NOVAC,DOAS technique,principal component analysis,volcanic SO2 emissions
更新于2025-09-10 09:29:36
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An improved glyoxal retrieval from OMI measurements
摘要： Satellite observations from the SCIAMACHY, GOME-2 and OMI spectrometers have been used to retrieve atmospheric columns of glyoxal (CHOCHO) with the DOAS method. High CHOCHO levels were found over regions with large biogenic and pyrogenic emissions, and hot-spots have been identified over areas of anthropogenic activities. This study focuses on the development of an improved retrieval for CHOCHO from measurements by the OMI instrument. From sensitivity tests, a fitting window and a polynomial degree are determined. Two different approaches to reduce the interference of liquid water absorption over oceanic regions are evaluated, achieving significant reduction of the number of negative columns over clear water regions. The impact of using different absorption cross-sections for water vapour is evaluated and only small differences are found. Finally, a high-temperature (boundary layer ambient: 294 K) absorption cross-section of nitrogen dioxide (NO2) is introduced in the DOAS retrieval to account for potential interferences of NO2 over regions with large anthropogenic emissions, leading to improved fit quality over these areas. A comparison with vertical CHOCHO columns retrieved from GOME-2 and SCIAMACHY measurements over continental regions is performed, showing overall good consistency. However, SCIAMACHY CHOCHO columns are systematically higher than those obtained from the other instruments. Using the new OMI CHOCHO data set, the link between fires and glyoxal columns is investigated for two selected regions in Africa. In addition, mapped averages are computed for a fire event in Russia between mid-July and mid-August 2010. In both cases, enhanced CHOCHO levels are found in close spatial and temporal proximity to elevated levels of MODIS fire radiative power, demonstrating that pyrogenic emissions can be clearly identified in the new OMI CHOCHO product.
关键词： anthropogenic activities,biogenic emissions,OMI,pyrogenic emissions,glyoxal,retrieval,satellite observations,DOAS
更新于2025-09-09 09:28:46
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Performance Analysis of a PV/Diesel Hybrid System for a Remote Area in Bangladesh: Effects of Dispatch Strategies, Batteries, and Generator Selection
摘要： This paper investigates the performance of PV/Diesel/Batt system for a stand-alone hybrid application in a remote community in Bangladesh meeting a load demand of 350kWh/day with a 74.34kW peak load demand. The effects of different dispatch strategies on the Cost of Energy (COE) and the Net Present Cost (NPC) using two major battery technologies (Lead Acid-LA and Lithium-ion) is studied. The study also extended to analyse the effects of selection of diesel generator in Hybrid Optimisation Model for Electric Renewables (HOMER) software tool on the performance indicators. Results indicate that the Combined Dispatch (CD) strategy has slightly lower Cost of Energy compared to the Load Following-LF and Cyclic Charging-CC strategies. However, operational emissions for Load Following Strategy is significantly lower than the other two strategies for both hybridised systems. The Renewable Fraction is greater in Load Following than the Combined Dispatch and Cyclic Charging strategies at the cost of Excess Energy (EE). The results also show that capital cost and the discount rate have a significant effect on Cost of Energy and Net Present Cost. However the fuel, battery, and PV module costs have negligible effects for both PV/Diesel/LA and the PV/Diesel/Li-ion-based hybrid systems.
关键词： Hybrid Energy,Battery Technology,Emissions,Dispatch Strategy,Renewable Fraction
更新于2025-09-09 09:28:46
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Observing atmospheric formaldehyde (HCHO) from space: validation and intercomparison of six retrievals from four satellites (OMI, GOME2A, GOME2B, OMPS) with SEAC<sup>4</sup>RS aircraft observations over the Southeast US
摘要： Formaldehyde (HCHO) column data from satellites are widely used as a proxy for emissions of volatile organic compounds (VOCs), but validation of the data has been extremely limited. Here we use highly accurate HCHO aircraft observations from the NASA SEAC4RS campaign over the Southeast US in August–September 2013 to validate and intercompare six operational and research retrievals of HCHO columns from four different satellite instruments (OMI, GOME2A, GOME2B and OMPS) and three different research groups. The GEOS-Chem chemical transport model provides a common intercomparison platform. We find that all retrievals capture the HCHO maximum over Arkansas and Louisiana, reflecting high emissions of biogenic isoprene, and are consistent in their spatial variability over the Southeast US (r=0.4–0.8 on a 0.5o×0.5o grid) as well as their day-to-day variability (r=0.5–0.8). However, all satellite retrievals are biased low in the mean by 20–51%, which would lead to corresponding bias in estimates of isoprene emissions from the satellite data. The smallest bias is for OMI-BIRA, which has the highest corrected slant columns and the lowest scattering weights in its air mass factor (AMF) calculation. Correcting the assumed HCHO vertical profiles (shape factors) used in the AMF calculation would further reduce the bias in the OMI-BIRA data. We conclude that current satellite HCHO data provide a reliable proxy for isoprene emission variability but with a low mean bias due both to the corrected slant columns and the scattering weights used in the retrievals.
关键词： SEAC4RS,OMPS,isoprene emissions,validation,satellite retrievals,HCHO,GEOS-Chem,Formaldehyde,GOME2B,OMI,GOME2A
更新于2025-09-04 15:30:14
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Effects of daily meteorology on the interpretation of space-based remote sensing of NO<sub>2</sub>
摘要： Retrievals of tropospheric NO2 columns from UV/visible observations of reflected sunlight require a priori vertical profiles to account for the variation in sensitivity of the observations to NO2 at different altitudes. These profiles vary in space and time but are usually approximated using models that do not resolve the full details of this variation. Currently, no operational retrieval simulates these a priori profiles at both high spatial and high temporal resolution. Here we examine the additional benefits of daily variations in a priori profiles for retrievals already simulating a priori NO2 profiles at sufficiently high spatial resolution to identify variations of NO2 within urban and power plant plumes. We show the effects of introducing daily variation into a priori profiles can be as large as 40% and 3×1015 molec. cm?2 for an individual day and lead to corrections as large as 10% for a monthly average in a case study of Atlanta, GA. Comparing an optimized retrieval to a more standard one, we find that NOx emissions estimated from space-based remote sensing can increase by ～100% when daily variations in plume location and shape are accounted for in the retrieval.
关键词： a priori profiles,emissions,satellite remote sensing,NO2,air quality
更新于2025-09-04 15:30:14
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Hybrid PV and wind grid-connected renewable energy system to reduce the gas emission and operation cost
摘要： This paper presents the methodology and results of the simulation and optimization of a hybrid renewable energy system for supply to a workstation reducing the gas emissions and the operation costs, so that to determinate the optimal system. The fundamentals equations used to estimate the operational costs are presented. The software used to simulate and optimize the purposed system is HOMER Pro?, this software can simulate energy systems with renewable fractions and optimize those systems to obtain the best system to use. In addition, the hybrid PV/Wind system replace 23.01 % of the grid purchases when they are working in parallel, the hybrid PV/Wind system take a reduction of the 12.46 % annual operation cost over the 100% of grid purchased and 9.3 % of the total operation cost over the 100% of the grid purchased. Finally, it can be concluded that the use of renewable energy systems takes greatest reductions on the supply systems if it takes the optimal design to develop the supply system.
关键词： Renewable energy systems,Hybrid PV & Wind system,Energy management system,Gas emissions
更新于2025-09-04 15:30:14
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The auroral red line polarisation: modelling and measurements
摘要： In this work, we model the polarisation of the auroral red line using the electron impact theory developed by Bommier et al. (2011). This theory enables the computation of the distribution of the Degree of Linear Polarisation (DoLP) as a function of height if the ?ux of precipitated electrons is provided as input. An electron transport code is used to infer the stationary electron ?ux at each altitude in the ionosphere as a function of energy and pitch angle. Using adequate cross-sections, the integral of this electron ?ux over energy and pitch angle provides an anisotropy parameter from which the theoretical local DoLP can be computed at each altitude. The modelled DoLP is then derived by integrating along the line-of-sight. Depending on the integration length, the modelled DoLP ranges between 0.6% for a very long integration length and 1.8% for a very short integration length localised around an altitude of 210 km. A parametric study is performed to check how the characteristics of the local DoLP (maximum value, altitude of the maximum, integrated height pro?le) vary. It is found that the polarisation is highly sensitive to the scattering function of the electrons, to the electron precipitation and to the geomagnetic activity. We compare these values to measured ones obtained during an observational campaign performed in February 2012 from Svalbard. The measured DoLP during the campaign was 1.9% ± 0.1%. The comparison between this value and the theoretical one is discussed. Discrepancies may be due to the poor constraint of the input parameters (thermosphere and ionosphere), to the fact that only electron precipitation is considered in this approach (and not proton precipitation for instance) and to the dif?culty in constraining the exact width of the emission layer in the thermosphere.
关键词： Auroral emissions,Polarisation,Thermosphere
更新于2025-09-04 15:30:14
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The First 2D Hybrid Perovskite Ferroelectric Showing Broadband White-Light Emission with High Color Rendering Index
摘要： Luminescent ferroelectrics have attracted considerable attention in terms of integrated photoelectronic devices, most of which are focused on the multicomponent systems of rare-earth doping ferroelectric ceramics. However, bulk ferroelectricity with coexistence of strong white-light emission, especially in the single-component system, remains quite rare. Here, a new organic–inorganic hybrid ferroelectric of (C4H9NH3)2PbCl4 (1) is reported, adopting a 2D layered perovskite architecture, which exhibits an unprecedented coexistence of notable ferroelectricity and intrinsic white-light emission. Decent above-room-temperature spontaneous polarization of ≈2.1 μC cm?2 is confirmed for 1. Particularly, it also exhibits brilliant broadband white-light emission with a high color-rendering-index up to 86 under UV excitation. Structural analyses indicate that ferroelectricity of 1 originates from molecular reorientation of dynamic organic cations, as well as significant structural distortion of PbCl6 octahedra that also contribute to its white-light emission. This work paves an avenue to design new hybrid ferroelectrics for multifunctional application in the photoelectronic field.
关键词： organic–inorganic hybrids,ferroelectrics,white-light emissions,perovskites,2D materials
更新于2025-09-04 15:30:14
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Laboratory precision measurements of optical emissions from coronal iron
摘要： Total solar eclipses, as the recent one seen across North America, are rare opportunities for optical spectroscopy of the corona. In view of the dearth of accurate rest-frame wavelength data, we measured 11 of the strongest optical coronal lines belonging to Fe X-XIV thereby proving the existence of the Fe XII line at 290.385(8) nm. Four lines, such as the green coronal line at 530.28113(13) nm, were measured with unprecedented precision, allowing in principle for absolute velocity determinations of plasmas with uncertainties of 0.08 km s?1. These results furthermore stringently benchmark the theory of complex open-3p-shell ions.
关键词： solar eclipses,coronal iron,optical emissions,spectroscopy,precision measurements
更新于2025-09-04 15:30:14
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Calibration and instrumental line shape characterization of a set of portable FTIR spectrometers for detecting greenhouse gas emissions
摘要： A comprehensive calibration procedure for mobile, low-resolution, solar-absorption FTIR spectrometers, used for greenhouse gases observations, is developed. These instruments commend themselves for campaign use and deployment at remote sites. The instrumental line shape (ILS) of each spectrometer has been thoroughly characterized by analyzing the shape of H2O signatures in open path spectra. A setup for the external source is suggested and the invariance of derived ILS parameters with regard to chosen path length is demonstrated. The instrumental line shape characteristics of all spectrometers were found to be close to nominal. Side-by-side solar observations before and after a campaign, which involved shipping of all spectrometers to a selected target site and back, are applied for verifying the temporal invariability of instrumental characteristics and for deriving intercalibration factors for XCO2 and XCH4, which take into account residual differences of instrumental characteristics. An excellent level of agreement and stability was found between the different spectrometers: the uncorrected biases in XCO2 and XCH4 are smaller than 0.01 and 0.15 %, respectively, and the drifts are smaller than 0.005 and 0.035 %. As an additional sensitive demonstration of the instrumental performance we show the excellent agreement of ground pressure values obtained from the total column measurements of O2 and barometric records. We find a calibration factor of 0.9700 for the spectroscopic measurements in comparison to the barometric records and a very small scatter between the individual spectrometers (0.02 %). As a final calibration step, using a co-located TCCON (Total Carbon Column Observation Network) spectrometer as a reference, a common scaling factor has been derived for the XCO2 and XCH4 products, which ensures that the records are traceable to the WMO in situ scale.
关键词： calibration,XCO2,XCH4,FTIR spectrometers,instrumental line shape,greenhouse gas emissions
更新于2025-09-04 15:30:14