Chemical Species Profiles Research Articles

Impacts of Organic Ice Condensation on the Optical Properties of Haze on Pluto

The flyby of the New Horizons spacecraft in 2015 July revealed an unexpected cold atmosphere of Pluto and confirmed the existence of its atmospheric haze. The observed and simulated vertical profiles of chemical species and microphysical processes suggest that the haze particles in Pluto’s middle and lower atmosphere may contain organic ice condensation. Such organic ice components can potentially affect Pluto’s haze chemistry and optical properties, as well as its energy budget. This study investigates the influence of the ice components on the scattering properties of Pluto’s haze by comparing New Horizons observations and simulated particle scattering properties. Comprehensive tests are performed for various haze particle parameters, including their size, chemical component, ice content, and morphology. Scattering properties of these ice-bearing haze particles are calculated by a discrete dipole approximation method and compared to multispectral observations obtained by four New Horizons instruments in spectral regions ranging from the ultraviolet to the near-infrared. The results indicate that the inclusion of the organic ice component leads to higher ratios of backscattering in the visible to extinction in the ultraviolet and provides better agreement with observations compared to monodispersed homogeneous aggregates. But it alone is not sufficient to explain the observed forward scattering values in the visible and near-infrared. Therefore, other scattering sources and/or mechanisms are still required to explain the full set of scattering observations. Further observations, as well as laboratory measurements and numerical tests, are anticipated to improve our understanding of the morphology and ice content of Pluto’s haze.

Simulation and optimization of direct glucose fuel cell

This work develops an unsteady state, nonisothermal, and three-dimensional model of the anion exchange membrane direct glucose fuel cell (AEM-DGFC). The model includes heat transfer and mass transports across DGFC, the reaction kinetics of catalyst layers, and the Ohmic resistance of the AEM electrolyte. The governing equations are solved numerically by the method of lines. The model predicts the concentration profiles of various chemical species and the temperature distributions in various fuel cell layers, during the transient startup period. The steady state model predictions agree well with the previous experimental data. The anodic overpotential is high relative to the cathodic, and the Ohmic overpotentials are due to the complex kinetics of the glucose electro-oxidation. The increases in the limited glucose and potassium hydroxide concentrations are shown to elevate the DGFC operation. Specifically, the cell performance is enhanced with increasing operating temperature, cathode side pressure, pressure drop across fuel cell, and porosity of catalyst layer, whereas the cell voltage diminishes with increasing membrane thickness. In summary, the optimal operating conditions are the operating temperature of 340 K, the cathode side pressure of 3 atm, the pressure drop of 0.036 atm, the membrane thickness of 0.0035 cm, and the catalysis layer porosity of 0.45.

Mechanistic Model and Optimization of the Diclofenac Degradation Kinetic for Ozonation Processes Intensification

This work focused on estimating the rate constants for three ozone-based processes applied in the degradation of diclofenac. The ozonation (Oz) and its intensification with catalysis (COz) and photocatalysis (PCOz) were studied. Three mathematical models were evaluated with a genetic algorithm (GA) to find the optimal values for the kinetics constants. The Theil inequality coefficient (TIC) worked as a criterion to assess the models’ deviation. The diclofenac consumption followed a slow kinetic regime according to the Hatta number (Ha<0.3). However, it strongly contrasted with earlier studies. The obtained values for the volumetric rate of photon absorption (VRPA) corresponding to the PCOz process (1.75×10−6 & 6.54×10−7 Einstein L−1 min−1) were significantly distant from the maximum (2.59×10−5 Einstein L−1 min−1). The computed profiles of chemical species proved that no significant amount of hydroxyl radicals was produced in the Oz, whereas the PCOz achieved the highest production rate. According to this, titanium dioxide significantly contributed to ozone decomposition, especially at low ozone doses. Although the models’ prediction described a good agreement with the experimental data (TIC<0.3), the optimization algorithm was likely to have masked the rate constants as they had highly deviated from already reported values.

PAHs controlling soot nucleation in 0.101—0.811MPa ethylene counterflow diffusion flames

On the heels of a recent study in an atmospheric pressure ethylene diffusion flame in which the transition from parent fuel molecule to Polycyclic Aromatic Hydrocarbons (PAHs) and, eventually, soot was studied by spatially resolved measurements of PAH concentrations and soot quantities, we extended the focus to diffusion flames with self- similar structure in the 0.101–0.811 MPa pressure range. To that end, we complemented pyrometry based measurements of soot volume fraction with light scattering measurements that, once corrected for beam steering, yielded soot particle size and number concentration profiles. A chemistry model, that had been validated for all species up to 3 ring aromatics in one of the flames investigated at each pressure and up to 4-rings for the flame at atmospheric pressure, was used to compare profiles of chemical species to those of soot quantities. Further analysis yielded the assessment of number nucleation rates of soot and their comparison to the dimerization rates of PAHs. Soot nucleation rate is consistent only with the dimerization of one- and two-ring PAHs, an observation that confirms findings in the atmospheric pressure flame. Changes in pressure and temperature have a progressively larger impact on the concentration of aromatics of increasingly larger molecular weight and, even more so, on soot volume fraction and nucleation rate. A four-fold increase in pressure from 0.101 MPa to 0.405 MPa increases the soot nucleation rate and PAH dimerization rate in flames with constant peak temperature, which is primarily a concentration effect on bimolecular collision rates; a similar but less pronounced effect is observed in the higher (0.405–0.811 MPa) pressure range. Changes in pressure and temperature tend to be progressively more consequential on aromatics of increasing molecular weight and soot.

Experimental and modeling study of the high-temperature combustion chemistry of tetrahydrofurfuryl alcohol

Lignocellulosic tetrahydrofuranic (THF) biofuels have been identified as promising fuel candidates for spark-ignition (SI) engines. To support the potential use as transportation biofuels, fundamental studies of their combustion and emission behavior are highly important. In the present study, the high-temperature (HT) combustion chemistry of tetrahydrofurfuryl alcohol (THFA), a THF based biofuel, was investigated using a comprehensive experimental and numerical approach.Representative chemical species profiles in a stoichiometric premixed methane flame doped with ∼20% (molar) THFA at 5.3 kPa were measured using online gas chromatography. The flame temperature was obtained by NO laser-induced fluorescence (LIF) thermometry. More than 40 chemical products were identified and quantified. Many of them such as ethylene, formaldehyde, acrolein, allyl alcohol, 2,3-dihydrofuran, 3,4-dihydropyran, 4-pentenal, and tetrahydrofuran-2-carbaldehyde are fuel-specific decomposition products formed in rather high concentrations. In the numerical part, as a complement to kinetic modeling, high-level theoretical calculations were performed to identify plausible reaction pathways that lead to the observed products. Furthermore, the rate coefficients of important reactions and the thermochemical properties of the related species were calculated. A detailed kinetic model for high-temperature combustion of THFA was developed, which reasonably predicts the experimental data. Subsequent rate analysis showed that THFA is mainly consumed by H-abstraction reactions yielding several fuel radicals that in turn undergo either β-scission reactions or intramolecular radical addition that effectively leads to ring enlargement. The importance of specific reaction channels generally correlates with bond dissociation energies. Along THFA reaction routes, the derived species with cis configuration were found to be thermodynamically more stable than their corresponding trans configuration, which differs from usual observations for hydrocarbons.

Investigation of door width towards flame tilting behaviours and combustion species in compartment fire scenarios using large eddy simulation

Numerical assessment on a large-scale compartment buoyant fires was performed to investigate the effect of exit door width on the flame tilting behaviour, evolution of the thermal layer and formation of combustion species. The simulations were performed using an in-house large eddy simulation (LES) based fire field model incorporating subgrid-scale (SGS) turbulence, detailed chemical kinetics combustion, soot and radiation models. A comprehensive set of simulation case studies have been carried out with various doorway opening sizes, to investigate the influence of the incoming air entrainment towards the deflection angle of the flame. In addition, the changes in the thermal interface, neutral plane and major chemical species profiles (i.e. CO/CO2) are also studied in detail. The fire model was validated against experimental measurements. It was found that increasing the door width elevates the neutral plane height and its correlated layer height of concentrated toxic gases. In addition, there is a critical door width (4/6) that produced the minimum fire tilting angle, deviation from the minimum door width results in an increase in flame tilting angle. It was discovered the centre fire have a range of titling angle between 58° to 75°, with a variation of 25% from 2/6 to 8/6 doorway sizes. This also totally affects the dynamics of the CO2 profiles with the compartment room, in which the concentrated toxic gas layer ascends as the fire is more ventilated. In general, it was discovered that having a large doorway size is mainly contributing to reduce the potential fire hazards in a one-opening compartment room fire scenario. The relation of compartment fire tilting can be critical especially for the design of fire protection systems.

PM2.5 Filter Extraction Methods: Implications for Chemical and Toxicological Analyses.

Toxicology research into the global public health burden of fine particulate matter (PM2.5) exposures frequently requires extraction of PM2.5 from filters. A standardized method for these extractions does not exist, leading to inaccurate interlaboratory comparisons. It is largely unknown how different filter extraction methods might impact the composition and bioactivity of the resulting samples. We characterized the variation in these metrics by using equal portions of a single PM2.5 filter, with each portion undergoing a different extraction method. Significant differences were observed between extraction methods for concentrations of elements and polycyclic aromatic hydrocarbons (PAHs) for the PM2.5 tested following its preparation for biological response studies. Importantly, the chemical profiles differed from those observed when we used standard protocols for chemical characterization of the ambient sample, demonstrating that extraction can alter both chemical component amounts and species profiles of the extracts. The impact of these chemical differences on sensitive end points of zebrafish development was investigated. Significant differences in the percent incidence and timing of mortality were associated with the PM2.5 extraction method. This research highlights the importance of and rationale for considering the extraction method when interlaboratory comparisons of PM2.5 toxicology research are made.

3d cfd simulation of combustion in furnaces using mixture gases with variable composition

In the petroleum refining industry, furnaces are key equipment because they provide the necessary heat to carry out different processes. These furnaces are designed to use natural gas as fuel, but in most cases they use a mixture of waste gases known as refinery gases (RG), which molar composition varies depending on the process in which they are generated, in most cases with high content of propane, hydrogen, propylene, among others. This is done in most cases to save energy and reduce storage cost. However, this variation in molar composition also produces a change in calorific power that can be as high as 1,200 Btu/ft3, producing alterations in the combustion process, affecting efficiency and increasing pollutant emissions. In this work, the Computational Fluid Dynamics (CFD) technique is used to simulate the combustion process in a representative segment of a typical refinery furnace using RG as fuel with 3 different molar compositions. Comparative CFD 3D simulation cases are performed to study the effect of molar composition variability in the temperature and chemical species profiles inside the furnace. The obtained results show that high contents of gases like propane, propylene or hydrogen increase the calorific power and peak temperature inside the furnace, but temperature profile distribution is less uniform. The chemical species profiles inside the furnace show that there is an increase in CO when using mixture gases with low CH4 content, which indicates that a more detailed study regarding air excess and flow is needed. The results are very important because they can be used as a tool for decision-making regarding the convenience to use or not refinery waste gases as fuels in furnaces and to stablish a starting point for a detailed study about the improvement of furnaces operation and process safety.

Spatiotemporal Variation in Composition of Submicron Particles in Santiago Metropolitan Region, Chile

The chemical composition of submicron particles (aerodynamic diameter Da < 1.0 μm) was investigated at three locations in the Santiago Metropolitan Region (SMR), Chile. Measurements campaigns were conducted in winter and spring 2016, at representative sites of a rural, urban and urban receptor environment. Instrumentation consisted of an optical analyzer to determine Black Carbon (BC) and the Aerosol Chemical Speciation Monitor (ACSM) to measure concentrations of particulate chloride (Cl-), nitrate (NO3-), sulfate (SO42-), ammonium (NH4+) and non-refractory carbonaceous species (organics). Complementary data, such as ozone concentration and meteorological parameters were obtained from the public air quality network. Results showed that in both the winter and spring seasons the organics predominated in the mass of submicron particles. This fraction was followed in decreasing order by NO3-, NH4+, BC, SO42- and Cl-. The highest average organics concentrations were measured in winter at the urban (32.2 µg m–3) and urban receptor sites (20.1 µg m–3). In winter, average concentrations of both NO3- and NH4+ were higher at the urban receptor site (12.3 and 4.5 µg m–3, respectively) when compared to the urban site (6.4 and 3.1 µg m–3, respectively). In general, all the measured species were present in higher concentrations during winter, excepting SO42-, which was the only one that increased during spring. The transition towards spring was also associated with an acidification of the aerosol at the rural and urban receptor site, while at the urban site the aerosol was observed alkaline. The highest average ozone concentration during both the winter and spring seasons were recorded at the urban receptor site (7.2 and 24.0 ppb, respectively). The study reports data showing that the atmosphere in the SRM has a considerable load of particulate organic compounds, NO3- and NH4+, which are in higher concentrations at urban sites during the winter season. Based on wind patterns and the hourly profiles of chemical species, the study suggests that during daytime the polluted air masses from the urban center can move to the northeast part of the region (namely urban receptor site) leading to the formation of submicron particles as well as photochemical ozone.

A new method for depth profiling reconstruction in confocal microscopy

Confocal microscopy is commonly used to reconstruct depth profiles of chemical species in multicomponent systems and to image nuclear and cellular details in human tissues via image intensity measurements of optical sections. However, the performance of this technique is reduced by inherent effects related to wave diffraction phenomena, refractive index mismatch and finite beam spot size. All these effects distort the optical wave and cause an image to be captured of a small volume around the desired illuminated focal point within the specimen rather than an image of the focal point itself. The size of this small volume increases with depth, thus causing a further loss of resolution and distortion of the profile. Recently, we proposed a theoretical model that accounts for the above wave distortion and allows for a correct reconstruction of the depth profiles for homogeneous samples. In this paper, this theoretical approach has been adapted for describing the profiles measured from non-homogeneous distributions of emitters inside the investigated samples. The intensity image is built by summing the intensities collected from each of the emitters planes belonging to the illuminated volume, weighed by the emitters concentration. The true distribution of the emitters concentration is recovered by a new approach that implements this theoretical model in a numerical algorithm based on the Maximum Entropy Method. Comparisons with experimental data and numerical simulations show that this new approach is able to recover the real unknown concentration distribution from experimental profiles with an accuracy better than 3%.

Development and Application of a New PM2.5 Source Apportionment Approach

ABSTRACTDue to the similarity of PM2.5 chemical species profiles of different sources, time synchronization of source contributions and the uncertainties of source-oriented models, it is difficult to get a well-separated and relatively accurate PM2.5 source apportionment result, especially for the secondary components, when only one method was applied. A new PM2.5 source apportionment approach, combining the receptor models, source-oriented models and emission inventory, was developed in this study. The proposed method had following strengths: (1) it could identify the source contributions to secondary components; (2) target (or expected) sources were optional; (3) mixed sources could be avoided. The new approach was then applied in two typical cities in North China – Beijing and Tangshan, based on intensive PM2.5 observation results from 2011 to 2013. The source apportionment result indicated that the annual average contribution to PM2.5 in Tangshan was 7.4%, 21.5%, 7.6%, 18.0%, 14.5%, 10.9% and 20.0% for power, metallurgy, cement, coal combustion, vehicle, dust and other sources, respectively; the annual average contribution ratio for vehicle, industry and industrial coal combustion, residential coal combustion, dust and other sources in Beijing was 31.5%, 22.9%, 10.6%, 14.5% and 20.4%, respectively. Seasonal variation of the source contributions was also analyzed. The demonstration results showed that the combined method was feasible. In addition, the detailed source contribution results could also provide scientific support for making effective PM2.5 mitigation strategy.

Physicochemical Modeling for Hot Water Extraction of Birch Wood

This paper presents a model developed for hot water extraction of birch wood meal. Besides solids, two liquid phases are assumed in the system: liquid bound to a wood fiber wall and the other remaining external liquid. True chemical species, their reactions, and diffusion between the liquid phases are considered in the model. The breakdown of hemicellulose into short-chain polymers and monomeric sugar units is modeled by applying an accurate and computationally efficient population balance approach. State-of-the-art correlations and equations are used, thus aiming for a truly predictive model. Several thermodynamic and kinetic submodels are integrated to achieve additional information compared to models already presented in the literature. The presented model is capable of reproducing the measured concentration profiles of chemical species and molecular weight distribution of hemicellulose polymers as a function of the process conditions. The output concentration data are further utilized to calculate the...

Depth profiles in confocal optical microscopy: a simulation approach based on the second Rayleigh-Sommerfeld diffraction integral.

A method is presented for recovering the intensity depth profile, by confocal optical microscopy, in transparent and amorphous samples with low scattering. The response function of a confocal Raman microscope has been determined by using the second Rayleigh-Sommerfeld diffraction integral and scalar wave optics within paraxial approximation, taking into account the refractive index mismatch between the sample and the medium surrounding the objective lens. An iterative multi-fitting-scheme, based on the conjugate gradient method and Brent algorithm, allowed to fit several depth profile curves simultaneously and retrieve the beam waist, the signal amplitude and the position of the sample surface. The reliability and accuracy of the theoretical procedure has been investigated through comparison with experimental measurements of the Raman depth profiles for different pinhole diameters. The model is shown to provide accurate description of the effect of the mismatch of the refractive index and of the dependence of the Raman signal on the depth with discrepancies lower than 3%. This procedure constitutes a first step towards the development of a manageable theoretical framework, amenable to a relatively simple numerical implementation, for the solution of the 'inverse' problem of finding the correct reconstruction of unknown profiles of chemical species within the sample, starting from experimental information gathered from micro-Raman depth profiling.

On-board measurements of gaseous pollutant emission characteristics under real driving conditions from light-duty diesel vehicles in Chinese cities

A total of 15 light-duty diesel vehicles (LDDVs) were tested with the goal of understanding the emission factors of real-world vehicles by conducting on-board emission measurements. The emission characteristics of hydrocarbons (HC) and nitrogen oxides (NOx) at different speeds, chemical species profiles and ozone formation potential (OFP) of volatile organic compounds (VOCs) emitted from diesel vehicles with different emission standards were analyzed. The results demonstrated that emission reductions of HC and NOx had been achieved as the control technology became more rigorous from Stage I to Stage IV. It was also found that the HC and NOx emissions and percentage of O2 dropped with the increase of speed, while the percentage of CO2 increased. The abundance of alkanes was significantly higher in diesel vehicle emissions, approximately accounting for 41.1%–45.2%, followed by aromatics and alkenes. The most abundant species were propene, ethane, n-decane, n-undecane, and n-dodecane. The maximum incremental reactivity (MIR) method was adopted to evaluate the contributions of individual VOCs to OFP. The results indicated that the largest contributors to O3 production were alkenes and aromatics, which accounted for 87.7%–91.5%. Propene, ethene, 1,2,4-trimethylbenzene, 1-butene, and 1,2,3-trimethylbenzene were the top five VOC species based on their OFP, and accounted for 54.0%-64.8% of the total OFP. The threshold dilution factor was applied to analyze the possibility of VOC stench pollution. The majority of stench components emitted from vehicle exhaust were aromatics, especially p-diethylbenzene, propylbenzene, m-ethyltoluene, and p-ethyltoluene.

WRF-Chem 모형을 이용한 한반도 대기질 모의: 화학 초기 및 측면 경계 조건의 영향

There is an increasing need to improve the air quality over South Korea to protect public health from local and remote anthropogenic pollutant emissions that are in an increasing trend. Here, we evaluate the performance of the WRF-Chem (Weather Research and Forecasting-Chemistry) model in simulating near-surface air quality of major Korean cities, and investigate the impacts of time-varying chemical initial and lateral boundary conditions (IC/BCs) on the air quality simulation using a chemical downscaling technique. The model domain was configured over the East Asian region and anthropogenic MICS-Asia 2010 emissions and biogenic MEGAN-2 emissions were applied with RACM gaseous chemistry and MADE/SORGAM aerosol mechanism. Two simulations were conducted for a 30-days period on April 2010 with chemical IC/BCs from the WRF-Chem default chemical species profiles ('WRF experiment') and the MOZART-4 (Model for OZone And Related chemical Tracers version 4) ('WRF_MOZART experiment'), respectively. The WRF_MOZART experiment has showed a better performance to predict near-surface CO, , , and mixing ratios at 7 major Korean cities than the WRF experiment, showing lower mean bias error (MBE) and higher index of agreement (IOA). The quantitative impacts of the chemical IC/BCs have depended on atmospheric residence time of the pollutants as well as the relative difference of chemical mixing ratios between the WRF and WRF_MOZART experiments at the lateral boundaries. Specifically, the WRF_MOZART experiment has reduced MBE in CO and O3 mixing ratios by 60~80 ppb and 5~10 ppb over South Korea than those in the WRF-Chem default simulation, while it has a marginal impact on and mixing ratios. Without using MOZART-4 chemical IC, the WRF simulation has required approximately 6-days chemical spin-up time for the East Asian model domain. Overall, the results indicate that realistic chemical IC/BCs are prerequisite in the WRF-Chem simulation to improve a forecast skill of local air quality over South Korea, even in case the model domain is sufficiently large to represent anthropogenic emissions from China, Japan, and South Korea.

장기간 (1990 ~ 2012) 측정자료를 이용한 용인-수원지역에서의 PM&lt;sub&gt;2.5&lt;/sub&gt;의 화학적 특성연구 및 헤이즈와 황사 현상 시 화학성분별 질량분율표의 개발

장기간 (1990 ~ 2012) 측정자료를 이용한 용인-수원지역에서의 PM&lt;sub&gt;2.5&lt;/sub&gt;의 화학적 특성연구 및 헤이즈와 황사 현상 시 화학성분별 질량분율표의 개발

Uncertainties of simulated aerosol optical properties induced by assumptions on aerosol physical and chemical properties: An AQMEII-2 perspective

The calculation of aerosol optical properties from aerosol mass is a process subject to uncertainty related to necessary assumptions on the treatment of the chemical species mixing state, density, refractive index, and hygroscopic growth. In the framework of the AQMEII-2 model intercomparison, we used the bulk mass profiles of aerosol chemical species sampled over the locations of AERONET stations across Europe and North America to calculate the aerosol optical properties under a range of common assumptions for all models. Several simulations with parameters perturbed within a range of observed values are carried out for July 2010 and compared in order to infer the assumptions that have the largest impact on the calculated aerosol optical properties. We calculate that the most important factor of uncertainty is the assumption about the mixing state, for which we estimate an uncertainty of 30–35% on the simulated aerosol optical depth (AOD) and single scattering albedo (SSA). The choice of the core composition in the core–shell representation is of minor importance for calculation of AOD, while it is critical for the SSA. The uncertainty introduced by the choice of mixing state choice on the calculation of the asymmetry parameter is the order of 10%. Other factors of uncertainty tested here have a maximum average impact of 10% each on calculated AOD, and an impact of a few percent on SSA and g. It is thus recommended to focus further research on a more accurate representation of the aerosol mixing state in models, in order to have a less uncertain simulation of the related optical properties.

Observations of surface radiation and stratospheric processes at Thule Air Base, Greenland, during the IPY

&lt;p&gt;Ground-based measurements of atmospheric parameters have been carried out for more than 20 years at the Network for the Detection of Atmospheric Composition Change (NDACC) station at Thule Air Base (76.5°N, 68.8°W), on the north-western coast of Greenland. Various instruments dedicated to the study of the lower and middle polar atmosphere are installed at Thule in the framework of a long standing collaboration among Danish, Italian, and US research institutes and universities. This effort aims at monitoring the composition, structure and dynamics of the polar stratosphere, and at studying the Arctic energy budget and the role played by different factors, such as aerosols, water vapour, and surface albedo. During the International Polar Year (IPY), in winter 2008-2009, an intensive measurement campaign was conducted at Thule within the framework of the IPY project “Ozone layer and UV radiation in a changing climate evaluated during IPY” (ORACLE-O3) which sought to improve our understanding of the complex mechanisms that lead to the Arctic stratospheric O&lt;span&gt;&lt;sub&gt;3&lt;/sub&gt;&lt;/span&gt; depletion. The campaign involved a lidar system, measuring aerosol backscatter and depolarization ratios up to 35 km and atmospheric temperature profiles from 25 to 70 km altitude, a ground-based millimeter-wave spectrometer (GBMS) used to derive stratospheric mixing ratio profiles of different chemical species involved in the stratospheric ozone depletion cycle, and then ground-based radiometers and a Cimel sunphotometer to study the Arctic radiative budget at the surface. The observations show that the surface radiation budget is mainly regulated by the longwave component throughout most of the year. Clouds have a significant impact contributing to enhance the role of longwave radiation. Besides clouds, water vapour seasonal changes produce the largest modification in the shortwave component at the surface, followed by changes in surface albedo and in aerosol amounts. For what concerns the middle atmosphere, during the first part of winter 2008-2009 the cold polar vortex allowed for the formation of polar stratospheric clouds (PSCs) which were observed above Thule by means of the lidar. This period was also characterized by GBMS measurements of low values of O&lt;span&gt;&lt;sub&gt;3&lt;/sub&gt;&lt;/span&gt; due to the catalytic reactions prompted by the PSCs. In mid-January, as the most intense Sudden Stratospheric Warming event ever observed in the Arctic occurred, GBMS and lidar measurements of O&lt;span&gt;&lt;sub&gt;3&lt;/sub&gt;&lt;/span&gt;, N&lt;span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;/span&gt;O, CO and temperature described its evolution as it propagated from the upper atmosphere to the lower stratosphere.&lt;/p&gt;

A multiscale modeling of carbon dioxide absorber and stripper using the Karhunen–Loève Galerkin method

A multiscale packed bed model is proposed to simulate industrial carbon dioxide absorber and stripper employing the hot potassium carbonate process promoted by piperazine. At a macro scale, a material and energy balance for the packed bed is built with the consideration of basic reaction chemistry, phase equilibria and solution thermodynamics, where the facilitated mass transfer of CO2 caused by chemical reactions is taken care of by an enhancement factor. At a micro scale, the enhancement factor is calculated from the concentration profiles of chemical species in the liquid film around packing materials. The computational burden for the numerical solution of a set of diffusion–reaction equations at each macro scale location is circumvented by means of the Karhunen–Loève Galerkin (KLG) method. The present multiscale model, where the KLG method treats the micro scale process of diffusion and reaction in the liquid film, is found to yield accurate predictions at a reasonably small computational cost. This method of solving multiscale problems can be applied not only to the present CO2 absorption/desorption processes but also to various systems in science and engineering, where the necessity of multiscale resolution is important.

Reduced-order modeling of carbon dioxide absorption and desorption with potassium carbonate promoted by piperazine

Carbon dioxide emitted from the power plants may be removed in an absorber-stripper unit, where CO2 mass transfer enhanced by chemical reactions occurs. The mass transfer enhancement factor can be found accurately once we find the CO2 profile in the liquid film around a packing material. However, it costs a tremendous amount of computer time to solve governing diffusion–reaction equations for the relevant chemical species at each grid point of the packed bed to determine the enhancement factor accurately. Therefore, in the traditional models of packed bed, one adopts an approximate enhancement factor found from a simple model. In the present work, we employ the Karhunen–Loève Galerkin (KLG) method for the solution of the diffusion–reaction equations describing the CO2 absorption with potassium carbonate promoted by piperazine in the liquid film. With the KLG method, the computational time for the diffusion–reaction equations is reduced drastically and the rigorous model for the enhancement factor can be adopted in the industrial packed beds. The resulting reduced order model is found to predict the concentration profiles of chemical species accurately. It shall be adopted in the multiscale model for a packed bed, where the macro scale describes the overall geometry of the packed bed and the micro scale describes the transport and reaction in the thin liquid film around a packing at an arbitrary macro location in the bed.