Sink Term Research Articles

Application of mathematical model on deposition study of pumped-storage power reservoir

Sediment deposition can cause a reduction in reservoir capacity and hydro-mechanical abrasion of pumped-storage power stations (PSPSs). To increase the operating efficiency and service life of PSPSs, sediment deposition in the process of reservoir water transfer needs to be addressed. Combined with hydrodynamics, reservoir sedimentation theory and a numerical model, a two-dimensional sediment model of the lower reservoir of Tianchi PSPS was established. Considering the characteristics of the upper and lower reservoirs of this PSPS, water and sediment exchange between the reservoirs was realised by setting source and sink terms. The process and distribution of sediment deposition were analysed over 50 years. Sediment deposition in the lower reservoir of the PSPS was found to be 0.5–1.8 km in front of the dam and triangular. The main stream of sediment-carrying flow could be moved from the right-hand channel to the sediment discharge tunnel and spillway by setting up a sediment discharge trench. The average sedimentation thickness of the reservoir during 10 years of operation was about 0.8 m with a sediment intercept weir (SIW) established, while it was more than 4.2 m in the main stream area outside the SIW. For operation of 50 years, these values were 3 m and 10 m, respectively. The SIW effectively reduced deposition near the inlet (outlet) of the PSPS, the amount of sediment passing the machine and deposition to the dam front. The results provide a reference for simulations and preventive measures of sediment deposition in PSPSs.

Analysis of Performance of Cavitation Models with Analytically Calculated Coefficients

Cavitation is often simulated using a mixture model, which considers the transport of an active scalar, namely the vapor fraction αv. Source and sink terms of the transport equation of αv, namely vaporization and condensation terms, rule the dynamics of the cavity and are described through different models. These models contain empirical coefficients generally calibrated through optimization processes. The purpose of this paper is to propose an analytical approach for the calculation of the coefficients, based on the time scales of vaporization and condensation processes. Four different models are compared considering as a test-case a two-dimensional flow around a cylinder. Some relevant quantities are analyzed both for standard value of coefficients, as found in the literature, and the coefficients calculated through the analytical approach. The study shows that the analytical computation of the coefficients of the model substantially improve the results, and the models considered give similar results, both in terms of cavitation regime and mean vapor fraction produced.

Probabilistic averaging in kinetic theory for colloidal transport in porous media

This paper develops a modified version of the Boltzmann’s equation for micro-scale particulate flow with capture and diffusion that describes the colloidal-suspension-nano transport in porous media. An equivalent sink term is introduced into the kinetic equation instead of non-zero initial data, resulting in the solution of an operator equation in the Fourier space and an exact homogenization. The upper scale equation is obtained in closed form together with explicit formulae for the large-scale model coefficients in terms of the micro-scale parameters. The upscaling reveals the delay in particle transport if compared with the carrier water velocity, which is a collective effect of the particle capture and diffusion. The derived governing equation generalizes the current models for suspension-colloidal-nano transport in porous media.

Exact Steady State of the Open XX -Spin Chain: Entanglement and Transport Properties

We study the reduced dynamics of open quantum spin chains of arbitrary length $N$ with nearest neighbour $XX$ interactions, immersed within an external constant magnetic field along the $z$ direction, whose end spins are weakly coupled to heat baths at different temperatures, via energy preserving couplings. We find the analytic expression of the unique stationary state of the master equation obtained in the so-called global approach based on the spectralization of the full chain Hamiltonian. Hinging upon the explicit stationary state, we reveal the presence of sink and source terms in the spin-flow continuity equation and compare their behaviour with that of the stationary heat flow. Moreover, we also obtain analytic expressions for the steady state two-spin reduced density matrices and for their concurrence. We then set up an algorithm suited to compute the stationary bipartite entanglement along the chain and to study its dependence on the Hamiltonian parameters and on the bath temperatures.

Modeling the interstitial fluid effect in turbulent disperse slurry flow in a vertical pipe

A numerical study was conducted to assess the performance of a Two-Fluid Model (TFM) developed for gas-solid flow in predicting liquid-solid flow, as well as a TFM specifically modified for liquid-solid flow, which considers the effect of the interstitial fluid. Both cases use the Kinetic Theory of Granular Flow (KTGF) for prediction of the solid phase flow features. Some of the physics involved in gas-solid and liquid-solid flows is intuitively different, and some model terms that can be neglected in a gas-solid formulation turn out to be important for liquid-solid flow. For instance, the much larger density and viscosity of the liquid compared to a gas suggest that the solid particle fluctuations and collisions are reduced. Three intermediate model formulations were developed to assess the relevance of the interstitial terms. The intermediate model formulations, together with the two base case models, were assessed based on their predictions for the case of fully developed, turbulent, steady flow of a liquid solid mixture in a vertical pipe. The main differences in the model formulations pertain to the transport equations for the streamwise liquid momentum, granular temperature and turbulence kinetic energy. The predictions considered such flow features as: the velocity profiles of both the liquid and solid phases, the solids volume fraction profile and budgets of the transport equations for the granular temperature and turbulence kinetic energy. The results obtained were used to identify the most significant model terms. These include modified formulations for the solids viscosity and granular temperature conductive coefficient to include the effects of the interstitial fluid. The single most important term was the model for the long-range particle fluctuations through the fluid, which played a dominant role in the balance of the turbulence kinetic energy and granular temperature transport equations. The present analysis demonstrates that this term should be reconfigured as a sink term in the granular temperature equation and a source term in the turbulence kinetic energy equation. With this modification, the numerical predictions were much closer to the experimental data, especially in terms of the solids volume fraction profile.

Anthropogenic climate change: the impact of the global carbon budget

Using time series data for the period 1959–2015, our empirical analysis examines the simultaneous effects of the individual components of the global carbon budget on temperature. Specifically, we explore the possible effects of carbon emissions caused by fossil fuel combustion, cement production, land-use change emissions, and carbon sinks (here in terms of land sink and ocean sink) on climate change. The simultaneous inclusion of carbon emissions and carbon sinks allows us to look at the coexistent and opposing effects of the individual components of the carbon budget and thus provides a holistic perspective from which to explore the relationship between the global carbon budget and global warming. The results reveal a significant positive effect of carbon emissions on temperature for both fossil fuels emissions and emissions from land-use change, confirming previous results concerning carbon dioxide and temperature. Further, while ocean sink does not seem to have a significant effect, we identify a temperature-decreasing effect for land sink.

A Global Model for Predicting Vacuum Drying of Used Nuclear Fuel Assemblies

A global model is proposed to simulate the drying process of used nuclear fuel assemblies under vacuum drying conditions. The transient model consists of a coupled mass and energy conservation equation with appropriate source and sink terms. The classic Hertz-Knudsen expression is employed to resolve the evaporation rate and the associated water mass depletion in the system. Both latent heat of vaporization and residual decay heat are considered as sink and source in the energy conservation, respectively. The model is employed to simulate vacuum drying of spent nuclear fuel rod storage systems. Multistage stepwise vacuuming of the system is emulated, and several parametric studies are conducted to identify their role in the drying process. The predicted temporal profiles show that the proposed model is able to capture qualitative trends of the water removal rate, hence the dryness level of the system. The model prediction is also compared against experiments where the amount of residual water after a standard vacuum drying procedure is quantified. The predictions are found to compare favorably with the experimental measurements.

Characteristics of small-scale motions in a dual-plane jet flow

In this study, direct numerical simulations are performed to investigate the spatial evolution of a dual-plane jet flow with Ld/L0 = 6, where Ld and L0 are the separation distance between the two jets and the jet width, respectively. The formation mechanism of the turbulent kinetic energy along the centerline can be quite different. In the reversal flow region, the transport equation of turbulent kinetic energy can be seen as the combination of the transport, convection, production, pressure, and viscous dissipation terms, whereas in the downstream combined region, it can be further simplified as the combination of convection and viscous dissipation terms. The gain of the centerline TKE mainly occurs in the vertical direction through the turbulence transport effects. Concerning the strain product process, in all three regions the strain self-amplification term is the dominant source term, whereas the enstrophy production and viscous dissipation terms are main sink terms. Two important aspects of small-scale motions are considered, one being the correlation between the vorticity vector and the corresponding eigenvectors of strain rate tensor and the other being the characteristics of invariant of the velocity gradient. The joint PDFs of the strain self-amplification and enstrophy production are highly squeezed in the vertical direction in the converging region. In contrast, in the reversal flow region, where the flow is still highly intermittent, the contour lines already take similar albeit slightly squeezed shapes as those in HIT. The joint PDFs of the second and third invariants in the reversal and highly intermittent flow region and the subsequent fully turbulent regions acquire the well-known ‘teardrop’ shape. It is demonstrated that even in the highly intermittent region, the characteristics of small-scale motions are already close to the fully developed flow. These above findings contribute to a better understanding of the dual-plane jet flows.

Evaluation of NOAA National Water Model Parameter Calibration in Semi-Arid Environments Prone to Channel Infiltration

AbstractThe NOAA National Water Model (NWM), maintained and executed by the NOAA National Weather Service (NWS) Office of Water Prediction, provides operational hydrological guidance throughout the Contiguous United States. Based on the WRF-Hydro model architecture developed by the National Center for Atmospheric Research (NCAR), the NWM was recently modified for semi-arid domains, by permitting it to explicitly resolve infiltration from ephemeral channels into the underlying channel bed as an added model sink term. To analyze the added value of channel infiltration in semi-arid environments, we calibrated NWM v2.1 (with the channel infiltration function) to 56 independent basins in the western CONUS, following identical calibration methods as the pre-operational NWM v2.1 (not including channel infiltration). Calibration of the model consists of two parts, including 1) calibration of channel infiltration only with other parameters set to the calibrated parameters used for pre-operational NWM v2.1 and 2) calibration of all parameters including channel infiltration with settings otherwise equivalent to the calibration of NWM v2.1. The calibrated channel-infiltration enhanced NWM improves predictive skill compared to the control NWM in 85% of evaluated basins, for the calibration period. The current NWM settings for physical processes and the biases of the calibration scheme limit model performance in semi-arid environments. To explore whether channel infiltration paired with an alternative calibration scheme could address these limitations, NWM v2.1 was calibrated with a new objective function in selected basins. We found that this updated objective function could ameliorate model biases in some semi-arid environments.

Effects of reactivity on mobility: insights from an exactly solvable two-state model

Recent experimental reports of activity-induced enhanced mobility by Wang et al (2020 Science 369 537) have renewed the debate about the reality of a phenomenon that, since its first observation in 2000, has been both reaffirmed and called into question. In an effort to find theoretical grounds for or against these observations, we apply a one-dimensional model of two-state Brownian dynamics to determine to what extent chemical reactivity, as represented in the equations of particle motion by source and sink terms that induce inter-state transitions, affects how much farther or nearer the particle travels on average in a time interval t in relation to the distance it would have traveled in the absence of a reaction. We find—based on exact calculations carried out in Laplace space—that depending on the strengths of the potentials that define the two states, as well as the locations of their minima and the speed of exchange between them, the particle’s relative displacement can be indeed be enhanced by substantial amounts, but it can also be decreased. While these findings do not necessarily resolve the questions around the boosted mobility effect, they do provide further evidence of its potential observability.

Taking a mass-balance approach to assess marine plastics in the South China Sea

The South China Sea (SCS) is recognised as a global hotspot for plastic pollution. We review available field studies and identify a significant lack of data needed to construct a simple mass balance box model for plastic pollution in the SCS. Fundamental information on plastic mass input, transfer and sink terms are simply not available. Also unknown are the rates of accumulation in different environments, the dispersal pathways of plastic particles of different density, the residence times of plastic in the water column and the rate at which macroplastics are transformed into microplastics in different environments. Filling these information gaps is critical for states to determine adequate response measures, including developing and tracking impact of policies to deal with the problem of plastic pollution in the SCS.

Modelling and simulation of multi-coupled heat and mass transfer processes: A case study of solar biomass dryer

This research aims to develop and simulate multi-coupled heat and mass transfer models for the solar-biomass drying process of agricultural products. The model took into account all the possible resistances to the transport processes by coupling the diffusion, source, or sink terms of the transport models. A stable numerical solution of the models was achieved by the finite difference method via the Crank-Nicolson scheme with a well-relaxed stability criterion(≪0.5). The results of the drying simulation yielded drying rate constants of0.0318-0.03061h-1, average drying efficiency of 0.129 – 0.145 and drying time of 48–144 h, for solar drying of plantain slices with and without a biomass furnace as a supplementary heat source. The simulated transport variables were used to validate the measured results sequel to the practical Biot numbers (≪0.1), which accounted for the agreement between the experimental and simulated results. Also, the simulated drying rate constant was in agreement with the Arrhenius postulated evaporation rate constant for the two drying methods. Moreover, the solar-biomass drying of the sliced plantain from the initial moisture of 0.67kgwater/kgds to the final moisture of 0.15kgwater/kgds was accomplished within 48 h of continuous drying whereas the solar drying took 144 h of quasi-continuous drying to achieve the same result. The present work suggests the automation or regulation of heat from the biomass furnace to achieve quality drying within a short drying time with higher energy utilization efficiency.

Mathematical Epidemiology through Transport Phenomena Viewpoint

With historical roots linked to life sciences, species diffusion has inspired dynamic models for infectious disease spreading. However, drawbacks have been raised towards the inclusion of people’s displacement effects, whose ordered motion might refer to species convection within transport phenomena perspective. By transcending usual geometric role of spatial coordinates, the present work proposes a surrogate mathematical description via dimensionless generalized coordinates as intended to categorize people, whether or not infected, in terms of age and comorbidities. Accordingly, while diffusive infection refers to random motion of categorized people, convective infection can be additionally invoked and assigned to “streamwise” (i.e., ontology-driven) people’s motion. With infected-people fraction as dimensionless dependent variable, the governing partial differential equation equally considers source and sink terms referring respectively to contamination-reinfection and recovery-death rates. Such epidemic transport model is preliminary applied to SARS-CoV-2 spreading (i.e., COVID-19 dynamics) among categorized people and trial numerical simulations are performed in view of extant infection data from Florida (USA), here taken as case study. Prospective extensions for the proposed epidemic transport model are addressed (e.g., diffusive infection in inhomogeneous media and human’s displacement rheology).

A Development of Pore Network Model Coupled Thermal Transport for Hydrophilic Porous Media of PEM Electrolyser

Hydrogen is a highly promising energy carrier vector. Water electrolysis process that provides splits of water to hydrogen and oxygen through the electricity has gained great recognition for hydrogen production because it provides high conversion efficiency, clean and purified hydrogen in recent years. A Polymer Electrolyte Membrane electrolyser that brings important advantages such as compactness, and the ability to work at low operating temperature, is an electrochemical device. From the gas channels in the cathode, the water enters the hydrophilic porous transport layer (PTL), also known as the gas diffusion layer (GDL), to the catalyst layer (CL) in which the electrolysis reactions occur.At high current densities (higher than 1 A/cm2), the PEM electrolyser is also favorable to produce a high amount of hydrogen; however, management of heat and mass transfer in the GDL becomes crucial as the two-phase flow occurs, and can be lead to hot spots. Moreover, the mass transport overpotentials become important issues at high current densities and lead to be 25% losses in the overall electrolyzer overpotential. A development of model is crucial to understand and enhance the heat and mass transport mechanisms in CL-GDL interface. Here, pore network model (PNM) has gained a significant interest as it offers strong tool to simulated multiphase flow in three-dimensional (3D) porous media for electrochemical energy conversion. The principle behind of this modelling approach is that a porous medium behaves as a network of pores that connected by throats. Through this framework, the discretization approach to transport modelling becomes dramatically simple, and the computational cost and time are reduced among the continuum modelling approaches (e.g., Lattice-Boltzmann, CFD).In this work, to the best knowledge of authors, the first pore network model coupled heat transfer model is developed to characterize available GDL. Here, the pore network is extracted from the micro CT image of a hydrophilic GDL through the Snow algorithm employed in OpenPNM software (An open-source Pore Network Modeling Package) and reconstructed in this environment, while the geometry of catalyst layer is created randomly. The effective two-phase 2D model is developed to predict water transport in the GDL and CL through the percolation algorithm. For this purpose, the sink and source terms are employed for some pores in the network (especially near GDL-CL interface) according to electrolyser operating conditions. Similarly, heat transport equations are applied for each pore in the network with adding source and sink terms due to the evaporation and condensation, respectively according to operating conditions. Therefore, under electrolyser operating conditions, the heat and mass transfer performance of GDL and especially in GDL-CL interface are investigated. Moreover, the effect of GDL-CL morphology (e.g., pore and throat sizes, and porosity) on heat and mass transport mechanism is investigated in detail.

Two-phase flow simulations of fixed 3D oscillating water columns using OpenFOAM: A comparison of two methods for modeling quadratic power takeoff

This study examines the performance of a numerical method that introduces an artificial sink term to the Reynolds-averaged Navier Stokes equations to simulate the flow through an orifice used as a quadratic Power Takeoff (PTO) for Oscillating Water Columns (OWCs). The method replaces the quadratic PTO by an artificial Forchheimer-flow region (referred to as the artificial Forchheimer-flow method). The performance of this method was evaluated by making comparisons with the existing experimental results for two OWCs and the numerical results obtained by using air-water two-phase flow simulations of the air flow through an orifice (referred to as the orifice-flow method). The surface elevations, velocity fields and pressure fields obtained by the orifice-flow and artificial Forchheimer-flow methods are compared. To use the artificial Forchheimer-flow method, an equation for specifying the Forchheimer coefficient is provided and the sensitivity of the pneumatic efficiency to the Forchheimer coefficient is discussed. It can be concluded that the artificial Forchheimer-flow method can satisfactorily reproduce the measured pneumatic efficiency, pressure field in the air, the velocity field in the water and the cross-sectional average velocity of the air. Compared to the orifice-flow method, the artificial Forchheimer-flow method can speed up the simulation by at least 25 times.

Indirect validation of fluid-to-fluid scaling criteria for modeling steam condensation based on empirical correlations and CFD simulations

Several nuclear reactor designs have adopted passive safety systems with condensation inside horizontal tubes, such as the Passive Auxiliary Feedwater System (PAFS) of the APR+, the new generation of the Korean-Standard Pressurized Water Reactors (PWR). Performing steam condensation experiments under high-pressure conditions is needed for the design and the realistic prediction of the condensation phenomena in such systems. To avoid the costs and technical complexities associated with experimentation at high-pressure conditions, a fluid-to-fluid scaling method to model high-pressure steam condensation with a simulant fluid, refrigerant for instance, had been developed. It was determined that the liquid-to-vapor density ratio, the Froude number, and the vapor Reynolds number should be preserved in order to guarantee the flow regime and heat transfer similarity between prototypes and models. The scope of the current work is to validate the developed scaling criteria. Due to the limitation of test data of different fluids with comparable test parameters, indirect validation is proposed based on two approaches. The first approach is based on empirical correlations, in which test data from one fluid are transferred to the equivalent conditions of the other fluid, the transferred data are then compared with condensation correlations to check the validity of the scaling method. The second approach is based on CFD calculations. A CFD model, using the commercial CFD code STAR-CCM+, for the simulation of condensation in hotizontal tubes is developed. The Fluid Film model is used for modeling the condensate film thickness and development. For modeling the phase change process, source and sink terms are introduced to the continuity, momentum, and energy equations at the interface between the vapor and the condensate film. The developed CFD model is then applied in the scaling criteria validation by using it to simulate the condensation phenomena of different models in one fluid and compare its results with the corresponding experimental data in other fluid. The validation results show good agreement between prototypes and their equivalent models, and show good feasibility and reasonable accuracy of the proposed scaling criteria.

Boltzmann's colloidal transport in porous media with velocity-dependent capture probability

Mathematical modeling of suspension-colloidal-nano transport in porous media at different scales has long been a fascinating topic of fluid mechanics. In this study, we discuss the multi-pore scale, where Boltzmann's approach of distributed velocities is valid, and average (homogenize) the micro-scale equation up to the core scale. The focus is on the filtration function (particle capture probability per unity trajectory length) that highly depends on the carrier fluid velocity. We develop a modified form of the Boltzmann equation for micro-scale particle capture and diffusion. An equivalent sink term is introduced into the kinetic equation instead of non-zero initial data, resulting in the solution of an operator equation in the Fourier space and an exact homogenization. The upper scale transport equation is obtained in closed form. The upscaled model contains the dimensionless delay number and large-scale dispersion and filtration coefficients. The explicit formulas for the large-scale model coefficients are derived in terms of the micro-scale parameters for any arbitrary velocity-dependent filtration function. We focus on three micro-scale models for the velocity-dependent particle capture rate corresponding to various retention mechanisms, i.e., straining, attachment, and inertial capture. The explicit formulas for large-scale transport coefficients reveal their typical dependencies of velocity and the micro-scale parameters. Treatment of several laboratory tests reveals close match with the modeling-based predictions.

Howland Forest, ME, USA: Multi-Gas Flux (CO2, CH4, N2O) Social Cost Product Underscores Limited Carbon Proxies

Forest carbon sequestration is a widely accepted natural climate solution. However, methods to determine net carbon offsets are based on commercial carbon proxies or CO2 eddy covariance research with limited methodological comparisons. Non-CO2 greenhouse gases (GHG) (e.g., CH4, N2O) receive less attention in the context of forests, in part, due to carbon denominated proxies and to the cost for three-gas eddy covariance platforms. Here we describe and analyze results for direct measurement of CO2, CH4, and N2O by eddy covariance and forest carbon estimation protocols at the Howland Forest, ME, the only site where these methods overlap. Limitations of proxy-based protocols, including the exclusion of sink terms for non-CO2 GHGs, applied to the Howland project preclude multi-gas forest products. In contrast, commercial products based on direct measurement are established by applying molecule-specific social cost factors to emission reductions creating a new forest offset (GHG-SCF), integrating multiple gases into a single value of merit for forest management of global warming. Estimated annual revenue for GHG-SCF products, applicable to the realization of a Green New Deal, range from ~$120,000 USD covering the site area of ~557 acres in 2021 to ~$12,000,000 USD for extrapolation to 40,000 acres in 2040, assuming a 3% discount rate. In contrast, California Air Resources Board compliance carbon offsets determined by the Climate Action Reserve protocol show annual errors of up to 2256% relative to eddy covariance data from two adjacent towers across the project area. Incomplete carbon accounting, offset over-crediting and inadequate independent offset verification are consistent with error results. The GHG-SCF product contributes innovative science-to-commerce applications incentivizing restoration and conservation of forests worldwide to assist in the management of global warming.

Risk assessment for airborne disease transmission by poly-pathogen aerosols.

In the case of airborne diseases, pathogen copies are transmitted by droplets of respiratory tract fluid that are exhaled by the infectious that stay suspended in the air for some time and, after partial or full drying, inhaled as aerosols by the susceptible. The risk of infection in indoor environments is typically modelled using the Wells-Riley model or a Wells-Riley-like formulation, usually assuming the pathogen dose follows a Poisson distribution (mono-pathogen assumption). Aerosols that hold more than one pathogen copy, i.e. poly-pathogen aerosols, break this assumption even if the aerosol dose itself follows a Poisson distribution. For the largest aerosols where the number of pathogen in each aerosol can sometimes be several hundred or several thousand, the effect is non-negligible, especially in diseases where the risk of infection per pathogen is high. Here we report on a generalization of the Wells-Riley model and dose-response models for poly-pathogen aerosols by separately modeling each number of pathogen copies per aerosol, while the aerosol dose itself follows a Poisson distribution. This results in a model for computational risk assessment suitable for mono-/poly-pathogen aerosols. We show that the mono-pathogen assumption significantly overestimates the risk of infection for high pathogen concentrations in the respiratory tract fluid. The model also includes the aerosol removal due to filtering by the individuals which becomes significant for poorly ventilated environments with a high density of individuals, and systematically includes the effects of facemasks in the infectious aerosol source and sink terms and dose calculations.

Investigation of several proxies to estimate sulfuric acid concentration under volcanic plume conditions

Abstract. Sulfuric acid (H2SO4) is commonly accepted as a key precursor for atmospheric new particle formation (NPF). However, direct measurements of [H2SO4] remain challenging, thereby preventing the determination of this important quantity, and, consequently, a complete understanding of its contribution to the NPF process. Several proxies have been developed to bridge the gaps, but their ability to predict [H2SO4] under very specific conditions, such as those encountered in volcanic plumes (including, in particular, high sulfur dioxide mixing ratios), has not been evaluated so far. In this context, the main objective of the present study was to develop new proxies for daytime [H2SO4] under volcanic plume conditions and compare their performance to that of the proxies available in the literature. Specifically, the data collected at Maïdo during the OCTAVE (Oxygenated organic Compounds in the Tropical Atmosphere: variability and atmosphere–biosphere Exchanges) 2018 campaign, in the volcanic eruption plume of the Piton de la Fournaise, were first used to derive seven proxies based on knowledge of the sulfur dioxide (SO2) mixing ratio, global radiation, condensation sink (CS) and relative humidity (RH). A specific combination of some or all of these variables was tested in each of the seven proxies. In three of them (F1–F3), all considered variables were given equal weight in the prediction of [H2SO4], whereas adjusted powers were allowed (and determined during the fitting procedure) for the different variables in the other four proxies (A1–A4). Overall, proxies A1–A4 were found to perform better than proxies F1–F3, with, in particular, improved predictive ability for [H2SO4] > 2 × 108 cm−3. The CS was observed to play an important role in regulating [H2SO4], whereas the inclusion of RH did not improve the predictions. A last expression accounting for an additional sink term related to cluster formation, S1, was also tested and showed a very good predictive ability over the whole range of measured [H2SO4]. In a second step, the newly developed proxies were further evaluated using airborne measurements performed in the passive degassing plume of Etna during the STRAP (Synergie Transdisciplinaire pour Répondre aux Aléas liés aux Panaches volcaniques) 2016 campaign. Increased correlations between observed and predicted [H2SO4] were obtained when the dependence of predicted [H2SO4] on the CS was the lowest and when the dependence on [SO2] was concurrently the highest. The best predictions were finally retrieved by the simple formulation of F2 (in which [SO2] and radiation alone were assumed to explain the variations in [H2SO4] with equal contributions), with a pre-factor adapted to the STRAP data. All in all, our results illustrate the fairly good capacity of the proxies available in the literature to describe [H2SO4] under volcanic plume conditions, but they concurrently highlight the benefit of the newly developed proxies for the prediction of the highest concentrations ([H2SO4] > 2–3 × 108 cm−3). Moreover, the contrasting behaviours of the new proxies in the two investigated datasets indicate that in volcanic plumes, like in other environments, the relevance of a proxy can be affected by changes in environmental conditions and that location-specific coefficients do logically improve the predictions.