Concentrations Of Chemical Species Research Articles

Analysis of activation energy in magnetohydrodynamic flow with chemical reaction and second order momentum slip model

This paper is communicated theoretically to study the collective effects of Arrhenius activation energy and binary chemically reactive species in the presence of the second order momentum slip model which has not been studied so far. To support these declaration in addition with electrically conducting boundary layer flow and heat transport have considered towards an exponential stretching sheet. The current study incorporates the impact of activation energy, temperature difference ratio parameter, 1st and 2nd order slip parameter, chemical reaction rate on fluid velocity, fluid temperature and concentration of chemical species are elaborated through graphically and discussed in detail. Appropriate transformations are betrothed to acquire nonlinear highly coupled ordinary differential equations (ODE's) from partial differential equations which are then solved numerically by employing finite difference collocation process that apply three-stage Lobatto IIIa scheme. The obtained results confirm that an excellent agreement is achieved with those available in open literature. It is found that concentration profile decreases in the presence of chemical reaction rate and temperature difference ratio parameter whereas opposite demeanour is seen for activation energy.

Comparing different methods for statistical modeling of particulate matter in Tehran, Iran

Particulate matter has major impacts on human health in urban regions, and Tehran is one of the most polluted metropolitan cities in the world, struggling to control this pollutant more than any other contaminant. PM2.5 concentrations were predicted by three statistical modeling methods: (i) decision tree (DT), (ii) Bayesian network (BN), and (iii) support vector machine (SVM). Collected data for three consecutive years (January 2013 to January 2016) were used to develop the models. Data from the initial 2 years were employed as the training data, and measurements from the last year were used for testing the models. Twelve parameters, covering meteorological variables and concentrations of several chemical species, were explored as potential predictors of PM2.5. According to the sensitivity analysis of PM2.5 by SVM and derived explicit equations from BN and DT, PM10, NO2, SO2, and O3 are the most important predictors. Furthermore, the impacts of the predictors on the PM2.5 were assessed which the chemical precursors’ influences indicated more in comparison with meteorological parameters. Capabilities of the models were compared to each other and the support vector machine was found to be the best performing, based on evaluation criteria. Nonetheless, the decision tree and Bayesian network methods also provided acceptable results. We suggest more studies using the SVM and other methods as hybrids would lead to improved models.

Effects of a porous dielectric in atmospheric-pressure plasma jets submerged in water

In this paper, the underwater performance of atmospheric-pressure plasma jets with and without a porous dielectric material is compared. The comparison included a multi-channel discharge plasma jet with a porous dielectric that served to generate microdischarges in the dielectric and thereby increased the plasma density, and a single-discharge jet of a typical pen-type atmospheric pressure plasma jet without a porous dielectric. In the analysis, the electrical and optical characteristics, concentration of reactive chemical species, and underwater sterilization performance were characterized. The multi-channel discharge plasma jet was found to effectively sterilize over 99.9% of the Escherichia coli. The decimal reduction times of the single- and multi-jets were 13.13 and 6.98 min, respectively, due to their physical and chemical properties. The results confirmed that the sterilization rate of the multi-channel discharge plasma jet was 1.88 times faster than that of the single-discharge jet.

Activation energy and binary chemical reaction effects in mixed convective nanofluid flow with convective boundary conditions

Abstract In this paper, we present a theoretical study of the combined effects of activation energy and binary chemical reaction in an unsteady mixed convective flow over a boundary of infinite length. The current study incorporates the influence of the Brownian motion, thermophoresis and viscous dissipation on the velocity of the fluid, temperature of the fluid and concentration of chemical species. The equations are solved numerically to a high degree of accuracy using the spectral quasilinearization method. Brownian motion was noted as the main process by which the mass is transported out of the boundary layer. The effect of thermophoretic parameter seems to be contrary to the expected norm. We expect the thermophoretic force to ‘push’ the mass away from the surface thereby reducing the concentration in the boundary layer, however, concentration of chemical species is seen to increase in the boundary layer with an increase in the thermophoretic parameter. The use of a heated plate of infinite length increased the concentration of chemical species in the boundary layer. The Biot number which increases and exceeds a value of one for large heated solids immersed in fluids increases the concentration of chemical species for its increasing values. Highlights Combined effects of activation energy and binary chemical reaction are proposed. Spectral quasi-linearization method (SQLM) is used for computer simulations. Use Arrhenius activation energy in the chemical species concentration. Validate the accuracy and convergence using residual error analysis.

Chemical Characteristics of Atmospheric Aerosol at Alaknanda Valley (Srinagar) in the Central Himalaya Region, India

Measurements of fine (PM2.5) and inhalable (PM10) particles were collected at the Alaknanda Valley in the heart of Garhwal region during December 2015–December 2016. Collected samples of PMs were analyzed for major chemical species as anions (F−, Cl−, SO42−, NO2− and NO3−) and cations (Na+, NH4+, K+, Ca2+ and Mg2+) by ion chromatography. During the study period, the concentrations of PM2.5 and PM10 were 78.7 ± 25.1 and 111.8 ± 23.4 μg m−3, respectively. The measured chemical species were found a large variability in different seasons due to the impact of emissions and meteorological parameters. The measured water-soluble (WS) chemical species of PM2.5 and PM10 were 43% (33.7 μg m−3) and 57% (64.2 μg m−3), respectively, with the highest concentrations during the winter season followed by summer, monsoon and post-monsoon seasons. A significant positive correlation was observed between NH4+ and other species (Cl−, SO42− and NO3−) in both PM2.5 and PM10, which indicates its presence in the atmosphere as ammonium salts. As a result, NH4+ play a crucial role in neutralization of acidic species in the winter season; however, the contrary feature was observed in the summer season where Ca2+ was responsible for the main neutralizing species, mainly transported from the inland region during the summer. Principal component analysis shows that secondary aerosol, biomass burning, and soil-driven dust were the possible sources of the measured species over the station. Further, air mass back trajectory analyses indicate that the highest mass concentrations of PMs and WS chemical species were in the post-monsoon season when the air masses pass from eastern Pakistan and western part of India over receptor site. In the winter season, the concentrations of PMs and WS species were highest (second) when the air masses transported from a long distance up to Southern Afghanistan covering with Pakistan and western part of India. In overall, the study suggests the long-range transport of pollutants plays a crucial role in the enhancement of PMs over Alaknanda valley region.

Especiação Química do Sulfato em Águas Subterrâneas do Domínio Hidrogeológico Sedimentar do Estado da Bahia - Brasil, Utilizando o Método Tableau

Especiação consiste em identificar as formas químicas de um elemento no meio aquático, ajudando a elucidar a origem, mobilidade, e o impacto das espécies predominantes na qualidade da água. Este trabalho utilizou o método Tableau para obter a especiação química do sulfato nas águas subterrâneas do domínio sedimentar do Estado da Bahia. A depender da espécie química, a água subterrânea pode ter sabor salgado ou amargo, além de efeito laxativo. Foram utilizados resultados do banco de dados hidrogeológicos da CERB para poços perfurados entre 2003-2013. A ênfase foi para poços com sulfato acima do limite de 250 mg L-1, estabelecido pela Portaria do Ministério da Saúde n° 2914/11. O Tableau transforma um problema químico num conjunto matemático de equações, com base nas reações químicas e constantes de equilíbrio. Após a aplicação do método, encontrou-se concentrações maiores para MgSO4(aq), seguido de CaSO4(aq) e NaSO4- e baixas concentrações de KSO4-. Conquanto a presença de uma espécie química dependa da ocorrência dos minerais envolvidos na litologia, este trabalho não verificou para a mesma litologia, a mesma concentração das espécies químicas nas águas subterrâneas. Também não foi possível verificar que as concentrações estavam associadas aos índices pluviométricos locais. Portanto, futuras pesquisas devem considerar outros fatores não estudados aqui, para determinar os fatores influentes na especiação química do sulfato nas águas subterrâneas do Estado da Bahia.

Gradual Deformation of Bacterial Cell Morphology Due to the Effect of Nonthermal Atmospheric Pressure Plasma Jet-Treated Water (PTW)

Treatment of distilled water by plasma jet in atmospheric air results the plasma treated water (PTW) which has the bactericidal properties. To improve the understanding and the methodology of the inactivation process, PTW has been applied on bacteria cell ( E. coli ) as the bacteria inactivation tool. PTW of different chemical strength is produced by changing the plasma irradiation time (1–20 min) on distilled water. The pH of distilled water decreases with plasma irradiation time and reaches below 4 after 10 min plasma irradiation. The correlation between the pH value of PTW and the concentration of different chemical species in it is shown in this paper. HNO3 is the main acidic compound of this PTW. Different chemical species (NO x , OH, H2O2) in the PTW have been identified and the effect of this PTW on bacteria cell is discussed in this paper. The cell inactivation increases with the increase of the ratio of bacteria cell suspended liquid volume to be treated to the PTW volume (tested for the ratio of 1:05 and 1:10) and the chemical strength of PTW. Moreover, gradual deformation of bacteria cell morphology due to the effect of PTW and the change of the cell morphology after direct plasma treatment have been observed by using scanning electron microscope.

Hypersensitivity and Applications of Cladding Modes of Optical Fibers Coated with Nanoscale Metal Layers

Theoretical and experimental results are presented to show that the complex effective index of the modes of optical fibers coated with non-uniform metal coatings of gold, silver, copper, or palladium, with thicknesses between 0 and 20 nm, acquire a greatly enhanced sensitivity to various forms of perturbations. Thickness changes of less than 1 nm can be measured as well as the binding of record low concentrations of chemical and biochemical species.

A numerical solution of the problem of crown forest fire initiation and spread

Mathematical model of forest fire was based on an analysis of known experimental data and using concept and methods from reactive media mechanics. The study takes in to account the mutual interaction of the forest fires and three-dimensional atmosphere flows. The research is done by means of mathematical modeling of physical processes. It is based on numerical solution of Reynolds equations for chemical components and equations of energy conservation for gaseous and condensed phases. It is assumed that the forest during a forest fire can be modeled as a two-temperature multiphase non-deformable porous reactive medium. A discrete analog for the system of equations was obtained by means of the control volume method. The developed model of forest fire initiation and spreading would make it possible to obtain a detailed picture of the variation in the velocity, temperature and chemical species concentration fields with time. Mathematical model and the result of the calculation give an opportunity to evaluate critical conditions of the forest fire initiation and spread which allows applying the given model for of means for preventing fires.

Using benzene as growth precursor for the carbon nanostructure synthesis in an inverse diffusion flame reactor

The synthesis of carbon nanostructures, (CNS), with tubular-like morphology were carried out over Ni and NiFe catalysts introduced into different inverse diffusion flames environments fueled with ethylene, ethylene-benzene and benzene. In general, only the ethylene and benzene-doped ethylene flames could produce CNS since the pure benzene flame favored the soot formation path. Although the addition of benzene into the flame favored the CNS production in mass and particle dimensions, a loss of quality of the internal structure of the tube walls was seen particularly when the NiFe catalyst was used. Three types of tubular structures were obtained depending of flame and catalytic system. The multi-walled carbon nanotubes were only observed in the ethylene flame (800 K–1400 K) over the Ni catalyst, while the hollowed and solid carbon nanofibers were observed in the ethylene-benzene flame (800 K–1200 K) over both the Ni-based and NiFe catalysts. Also, a small amount of carbon nano-onions were seen at the tip of the ethylene-benzene flame where temperature was closer to 1400 K. In all cases, the base-growth model was the dominant mechanism for the tubular CNS found at the periphery of the flame, a place where the most important chemical species concentration (CO, C2H2 C6H6 and H2) was higher enough for catalyst activation.

Assessment of combustion models for numerical simulations of a turbulent non-premixed natural gas flame inside a cylindrical chamber

ABSTRACTThis work presents a Computational Fluid Dynamics (CFD) study of the non-premixed combustion of natural gas with air in an axisymmetric cylindrical chamber, focusing on the contribution of the chemical reaction modeling on the temperature and the chemical species concentration fields. Simulations are based on the solution of mass, momentum, energy and chemical species conservation equations. Thermal radiation heat transfer in the combustion chamber is computed through the Discrete Transfer Radiation Method, and the Weighted-Sum-of-Gray-Gases model solves the dependence of gas absorption coefficient on the wavelength. Turbulence is modeled by the standard k-ε model. Regarding the combustion modeling, it is performed a comparison of solutions obtained with the combined Eddy Break-Up/Arrhenius (EBU/Arrhenius) and the Steady Laminar Diffusion Flamelet (SLDF) models. The finite volume method is employed to treat the differential equations. Among other results, the solution of the governing equations allows for the determination of the region where combustion takes place, the distribution of the chemical species and the velocity fields. The numerical results are compared to experimental measurements, showing varied agreements. Results indicate that, in this case, the EBU/Arrhenius model can predict the flame temperature and the concentration of the most important species with better accuracy than the more sophisticated SLDF model.

Entrained flow gasification. Part 2: Mathematical modeling of the gasifier using RANS method

CFD (RANS based) simulations of REGA-1 experimental campaign concerning gasification of glycol in an oxygen-nitrogen mixture have been carried out. The reacting flow-field has been computed using a number of turbulence models while turbulence-chemistry interactions have been modeled using either the Eddy Dissipation Concept (EDC) or the presumed PDF approach. Two global-chemistry schemes have been used: the (HVI1) scheme for glycol gasification and the extended Jones-Lindstedt scheme. Radiation has been computed using the Discrete Ordinate Method with a comprehensive analysis concerning absorption/emission of infrared radiation by gaseous molecules as well as absorption and scattering on droplets. The CFD-predictions of the near-atomizer region have been sensitive to and strongly dependent on the sub-models used; the spray sub-model and the chemical schemes are the most important. Good quality predictions of temperature and chemical species (CO,H2,CO2,H2O,CH4) concentrations at 300 mm and 680 mm distances from the atomizer have been obtained. The HVI1 global chemistry scheme has predicted very well not only the CO/CO2 ratios but also the trace concentrations of methane. The paper shows how to simplify the radiative heat transfer simulations without a significant loss in accuracy.

A Computational Fluid Dynamics Study of Turbulence, Radiation, and Combustion Models for Natural Gas Combustion Burner

This paper presents a Computational Fluid Dynamics (CFD) study of a natural gas combustion burner focusing on the effect of combustion, thermal radiation and turbulence models on the temperature and chemical species concentration fields. The combustion was modelled using the finite rate/eddy dissipation (FR/EDM) and partially premixed flame models. Detailed chemistry kinetics CHEMKIN GRI-MECH 3.0 consisting of 325 reactions was employed to model the methane combustion. Discrete ordinates (DO) and spherical harmonics (P1) model were employed to predict the thermal radiation. The gas absorption coefficient dependence on the wavelength is resolved by the weighted-sum-of-gray-gases model (WSGGM). Turbulence flow was simulated using Reynolds-averaged Navier-Stokes (RANS) based models. The findings showed that a combination of partially premixed flame, P1 and standard k-ε (SKE) gave the most accurate prediction with an average deviation of around 7.8% of combustion temperature and 15.5% for reactant composition (methane and oxygen). The results show the multi-step chemistry in the partially premixed model is more accurate than the two-step FR/EDM. Meanwhile, inclusion of thermal radiation has a minor effect on the heat transfer and species concentration. SKE turbulence model yielded better prediction compared to the realizable k-ε (RKE) and renormalized k-ε (RNG). The CFD simulation presented in this work may serve as a useful tool to evaluate a performance of a natural gas combustor.

Fully resolved simulations of single char particle combustion using a ghost‐cell immersed boundary method

A novel ghost‐cell immersed boundary method for fully resolved simulation of char particle combustion has been developed. The boundary conditions at the solid particle surface, such as velocity, temperature, density, and chemical species concentration, are well enforced through the present method. Two semiglobal heterogeneous reactions and one homogeneous reaction are used to describe the chemical reactions in the domain, and the Stefan flow caused by the heterogeneous reactions is considered. A satisfactory agreement can be found between the present simulation results and experimental data in the literature. The method is then used to investigate the combustion property of a char particle and the interaction between CO2 gasification and O2 oxidation. Furthermore, combustion effect on the exchange of mass, momentum and energy between gas‐ and solid‐ phase is explored. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2851–2863, 2018

Energy-Dispersive Total-Reflection Resonant Inelastic X-ray Scattering as a Tool for Elemental Speciation in Contaminated Water.

This work presents a state-of the-art analytical methodology, by which chemical state information on metallic elements is obtained for liquid samples in a fast and simple manner. This method overcomes limitations of conventional X-ray techniques, such as X-ray absorption spectroscopy, by applying resonant inelastic X-ray scattering under total reflection geometry (TRIXS). TRIXS is particularly applicable for the analysis of small quantity of liquid samples deposited on polished reflectors. This feature is relevant for the chemical speciation of metallic trace elements contained in water samples, since the degree of their toxicity depends crucially on the concentration of specific chemical species included. The analytical merits of the proposed methodology were studied at Elettra Sincrotrone Trieste and at the Brazilian Synchrotron Light Laboratory. Contaminated water samples with low concentration of different chromium and manganese compounds were measured. Results prove the analytical potential of the TRIXS technique in characterizing different chemical species of metallic elements in water samples.

Fluorescent probes for the simultaneous detection of multiple analytes in biology.

Many of the key questions facing cellular biology concern the location and concentration of chemical species, from signalling molecules to metabolites to exogenous toxins. Fluorescent sensors (probes) have revolutionised the understanding of biological systems through their exquisite sensitivity to specific analytes. Probe design has focussed on selective sensors for individual analytes, but many of the most pertinent biological questions are related to the interaction of more than one chemical species. While it is possible to simultaneously use multiple sensors for such applications, data interpretation will be confounded by the fact that sensors will have different uptake, localisation and metabolism profiles. An alternative solution is to instead use a single probe that responds to two analytes, termed a dual-responsive probe. Recent progress in this field has yielded exciting probes, some of which have demonstrated biological application. Here we review work that has been carried out to date, and suggest future research directions that will harness the considerable potential of dual-responsive fluorescent probes.

Quantitative determination of chemical species in high concentration ZnX2 (X = Br and I) media by steady state voltammetry on Pt ultramicroelectrode

In this article, we present the voltammetric approach to quantitatively determine zinc-halides (Zn-X−, X=Br and I) complexes in the high concentration ZnX2 solutions by the measurements of the steady state current, iss associated with electrochemical oxidation of X− on Pt ultramicroelectrode (UME). At first, iss from electro-oxidation of uncoordinated I− as a function of total concentration of I−, CI−, total in the ZnI2 solutions were deviated from the theoretical iss under the pure diffusion-controlled condition, iss,diffusion to the lower values, respectively. The deviation from iss,diffusion to the lower iss in the ZnI2 solutions cannot be explained by migration but is associated with Zn-I− complexation. From the Raman spectra, both ZnI3− and ZnI42− exist at CZnI2>0.25 M. Since only free I− can be electrochemically oxidized, CI−, free is decreased as CZnI2 becomes higher due to the consumption of free I− to form ZnI3− and ZnI42−. Therefore, CI−, free can be determined by the stability constants of ZnI3− and ZnI42−, β3, Zn−I− and β4, Zn−I−, which were estimated by the finite element analysis under the migration model. From β3, Zn−I and β4, Zn−I, the accurate concentration of chemical species (I−, Zn2+, ZnI3−, and ZnI42−) were able to be quantitatively determined. β2, Zn−Br, β3, Zn−Br, and β4, Zn−Br in the ZnBr2 solutions were also estimated by the same analytical approach, and the concentration of the chemical species (Br−, Zn+, ZnBr3−, and ZnBr42−) were plotted as a function of CBr−, total.The concentration of the chemical species in the ZnX2 solutions are further predicted as CX−, total becomes 14M, and the lowest limit of energy density in the suggested ZnX2 redox flow batteries (RFBs) is also discussed based on the estimated CX−, free as a function of CX−, total.

Electrical prediction of tortuosity in porous media

The fluid transport phenomena in porous materials such as concrete, is one of the main actions involved in the degradation of the structures lying in aggressive areas. This transport is governed by several physical and chemical parameters such as porosity, tortuosity, diffusion coefficient or concentration of chemical species. The main objective of this work is to quantify the tortuosity parameter by a non-destructive method. Tortuosity is a parameter with significant inflluence on the transfer and diffusion of particles in porous media. Indeed it takes account of the irregularity and sinuous transport paths in the pore structure of the material. The experimental program focuses on applying a non-destructive method for measuring the electrical conductivity of materials as glass beads and sand with different classes, saturated with NaCl solution at different concentration. The material is placed in a PVC cell of 50 mm diameter, equipped with two stainless steel electrodes connected to the measuring circuit. The tortuosity values obtained in this work are less than unity. This accords considerably with the values found in the literature, we also note that the variation of this parameter depends on the nature of the medium but also according to its geometrical properties.

Spatially and angularly resolved spectroscopy for in-situ estimation of concentration and particle size in colloidal suspensions.

Successful implementation of process analytical technology (PAT) hinges on the ability to make continuous or frequent measurements in-line or at-line of critical product attributes such as composition and particle size, the latter being an important parameter for particulate processes such as suspensions and emulsions. A novel probe-based spatially and angularly-resolved diffuse reflectance measurement (SAR-DRM) system is proposed. This instrument, along with appropriate calibration models, is designed for online monitoring of concentration of chemical species and particle size of the particulate species in process systems involving colloidal suspensions. This measurement system was investigated using polystyrene suspensions of various particle radius and concentration to evaluate its performance in terms of the information obtained from the novel configuration which allows the measurement of a combination of incident light at different angles and collection fibres at different distances from the source fibres. Different strategies of processing and combining the SAR-DRM measurements were considered in terms of the impact on partial least squares (PLS) model performance. The results were compared with those obtained using a bench-top instrument which was used as the reference (off-line) instrument for comparison purposes. The SAR-DRM system showed similar performance to the bench top reference instrument for estimation of particle radius, and outperforms the reference instrument in estimating particle concentration. The investigation shows that the improvement in PLS regression model performance using the SAR-DRM system is related to the extra information captured by the SAR-DRM configuration. The differences in SAR-DRM spectra collected by the different collection fibres from different angular source fibres are the dominant reason for the significant improvement in the model performance. The promising results from this study suggest the potential of the SAR-DRM system as an online monitoring tool for processes involving suspensions. Graphical abstract A probe designed to acquire diffuse reflectance measurements at different source-detector distances for three incidence angles 0°, 30° and 45° was used to estimate particle size and concentration of polystyrene beads in aqueous suspension using partial least squares calibration models.

Aerosol chemical compositions in the North China Plain and the impact on the visibility in Beijing and Tianjin

To better understand the characteristics of the chemical compositions of aerosols comprised of water soluble ions (WSIs) and carbonaceous aerosol (CA) and their impacts on the visibility throughout the North China Plain (NCP), four experimental sampling campaigns were carried out between June 2013 and May 2014. The sampling sites were located in Beijing, Xiangshan, Tianjin, Shijiazhuang, and Qinhuangdao. The air pollution episodes mainly occurred during the autumn and winter in the NCP. With regard to different particle size distributions, the ratio of anions to cations in the fine size (0.64) was greater than that in the coarse size (0.54) in the NCP. Coefficients of divergence indicate that aerosol pollution had similar characteristics in the five cities of the NCP and that the pollutants were characterized by mutual influences and regional transfer processes. There were different non-linear correlations between the visibility and mass concentrations of PM2.5 at different relative humidity (RH) conditions. When the RH was >70%, the visibility was <5km; this shows that, due to hygroscopic growth in a higher RH, the increase in PM2.1 resulted in a decrease in the visibility. The Interagency Monitoring of Protected Visual Environments (IMPROVE) method was used to estimate the light extinction coefficients (LEC) from the measured concentrations of chemical species. Organic matter (OM), ammonium nitrate (AN), and ammonium sulfate (AS) were the three dominant species that contributed to the LEC in Beijing and had the highest proportions of total contributions to the LEC in the summer, accounting for 32.2%, 25.9%, and 24.4%, respectively. The LEC of sea salts did not change much throughout the year and accounted for 4.1–5.3% in Beijing and 4.8–7.4% in Tianjin. According to the Ambient Air Quality Standard, the days were divided into pollutional days (PD) and attained days (AD). The increasing concentrations of AN, AS and OM resulted in an increase in the LEC in the NCP, which led to the occurrences of low visibility events during the autumn and winter. NH4+, NO3−, and SO42− mainly existed as fine size particles (diameter<2.1μm) in Beijing (73.5%, 80.7%, and 78.0% on PD and 63.3%, 79.4%, and 72.5% on AD, respectively) and Tianjin (81.0%, 80.6%, and 82.1% on PD and 71.5%, 44.3%, and 69.7% on AD, respectively). However, the CA originating mainly from fuel combustion also played an important part in the visibility impairment in the coarse size (2.1<diameter<9.0μm). According to a positive matrix factorization (PMF) model, 37.1% and 26.5% of the LEC came from secondary aerosols on PD in Beijing and in Tianjin, respectively. In addition, biomass burning, fuel combustion and fugitive dust were also important contributing sources of the LEC in the NCP.