Gas-phase Contaminants Research Articles

Investigation of the adsorption behaviour of toxic heavy metals and bacteria on two allotropes of low dimensional boron nitride: Implications for detection and elimination

In this research, the focus was on two 2D allotropes of boron nitride (BN), specifically Haeck-BN and Twin-BN. They exhibit unique structural and electronic characteristics, making them suitable for sensing applications. High surface area materials offer numerous affinity sites for heavy metal ions and toxic molecules. Using density functional theory (DFT), the adsorption mechanisms of various contaminants in gas (solvent) phase on both pristine and doped Haeck-BN and Twin-BN were investigated. Pronounced adsorption of arsenic (As) and lead (Pb) was observed on pristine Twin-BN sheets, with adsorption energies of −2.83 eV (−2.86 eV) and −2.03 eV (−2.39 eV), respectively. Haeck-BN showed weaker interactions, with adsorption energies of −1.48 eV (−1.55 eV) for As and −0.64 eV (−0.92 eV) for Pb. Significant adsorption of specific amino acids, integral components of bacterial cell walls, was noted on both pristine and silver-modified sheets. The electronic properties showed significant shifts upon molecular adsorption, confirming their sensitivity towards foreign contaminants. The high adsorption energies of amino acids suggest potential applications in efficient bacterial inactivation for water purification. While real-world scenarios pose challenges, the calculations provide valuable insights for potential use of these nanosheets in advanced water purification membrane technology.

Cross Contamination of 2,4,6-Trichloroanisole in Cork Stoppers.

Cork stoppers are the preferred choice for sealing bottled wines around the world. However, the quality of cork stoppers is also defined by the presence of 2,4,6-trichloroanisole (TCA), which gives the wine an unpleasant moldy/musty taste. It is a matter of concern for both cork stopper manufacturers and wine producers whether TCA can be transported between stoppers. As little is known about cross contamination between stoppers, this work provides enough experimental data to discuss the extent of TCA transfer in naturally contaminated stoppers in the liquid and gas phase that can be useful to the cork industry and the wine industry. We found that when a clean stopper is soaked together with a contaminated one in hydro-alcoholic solution, 12% of the TCA can be transferred. In gas-phase contamination, only stoppers with 12 ng/L, or more, contaminate clean stoppers when enclosed together for several days. In a second experiment, where clean corks were exposed to a controlled contaminated environment, it was found that TCA contamination was not confined to the outermost layer of the stoppers. Based on these findings, some recommendations are given to prevent TCA cross contamination between stoppers during the cork stopper manufacturing, storage, wine making, and bottling.

Recent Advances in Fly-Ash-Based Geopolymers: Potential on the Utilization for Sustainable Environmental Remediation.

This Mini-Review provides the fundamentals and the state-of-the-art overview on geopolymers, novel inorganic polymeric materials (also known as alkali-bounded ceramics), synthesized from aluminosilicate sources and explores their current and potential sustainable environmental applications. It summarizes and examines concisely the recent scientific advances on geopolymers widely synthesized from abundantly available fly-ash-based aluminosilicate materials via alkaline activation at relatively low temperatures. Although geopolymerization is not a new concept and has offered valuable solutions to some environmental challenges as a low-cost and environmentally benign alternative to conventional energy-intensive Portland cement-based construction materials and has also been used as a barrier in immobilizing toxic and radioactive metals, the application of this technology to produce effective adsorptive materials for mitigation of liquid- and gas-phase contaminants is relatively recent. The valorization of the fly-ash waste in the sustainable and cost-effective development of geopolymeric adsorbents and catalysts for the treatment and control of environmental contaminants and energy production and storage could lead to many economic benefits due to the low cost and resource recycling of this globally abundant raw material. Perspectives on the synthesis and utilization of new geopolymer-based adsorbents for environmental and energy applications with insights into future research directions, prospects, and challenges for economic large-scale production are addressed.

Removal of off-resonance xenon gas artifacts in pulmonary gas-transfer MRI.

Hyperpolarized xenon (129 Xe) gas-transfer imaging allows different components of pulmonary gas transfer-alveolar air space, lung interstitium/blood plasma (barrier), and red blood cells (RBCs)-to be assessed separately in a single breath. However, quantitative analysis is challenging because dissolved-phase 129 Xe images are often contaminated by off-resonant gas-phase signal generated via imperfectly selective excitation. Although previous methods required additional data for gas-phase removal, the method reported here requires no/minimal sequence modifications/data acquisitions, allowing many previously acquired images to be corrected retroactively. 129 Xe imaging was implemented at 3.0T via an interleaved three-dimensional radial acquisition of the gaseous and dissolved phases (using one-point Dixon reconstruction for the dissolved phase) in 46 human subjects and a phantom. Gas-phase contamination (9.5%±4.8%) was removed from gas-transfer data using a modified gas-phase image. The signal-to-noise ratio (SNR) and signal distributions were compared before and after contamination removal. Additionally, theoretical gaseous contaminations were simulated at different magnetic field strengths for comparison. Gas-phase contamination at 3.0T was more diffuse and located predominantly outside the lungs, relative to simulated 1.5T contamination caused by the larger frequency offset. Phantom experiments illustrated a 91% removal efficiency. In human subjects, contamination removal produced significant changes in dissolved signal SNR (+7.8%), mean (-1.4%), and standard deviation (-2.3%) despite low contamination. Repeat measurements showed reduced variance (dissolved mean, -1.0%; standard deviation, -8.4%). Off-resonance gas-phase contamination can be removed robustly with no/minimal sequence modifications. Contamination removal permits more accurate quantification, reduces radiofrequency stringency requirements, and increases data consistency, providing improved sensitivity needed for multicenter trials.

Metal contamination of silicon from the furnace atmosphere after crystallization

The contamination of silicon by the furnace atmosphere is investigated based on lab-scale annealing experiments in a carbon-based furnace. The analysis comprises measurements of charge carrier lifetime and interstitial iron as well as elemental analysis. An approach to obtain information on the concentration of the metal species involved in the contamination process based on charge carrier lifetime profiles is established. A significant reduction of the charge carrier lifetime below the sample surface is observed. This reduction is governed by iron and at least one (cobalt and/or nickel) faster diffusing species. The contributions from the furnace parts and the purging gas are investigated and possibilities to reduce the gas phase contamination are elaborated. The results indicate a possible relevance of gas phase contamination in crystallization experiments.

Application of and research on TiO2 photocatalysis technology

Nano-TiO2 photocatalysis technology is a new environmental pollutant purification technology, but its application is very extensive. This paper introduces the photocatalytic properties of nano-TiO2, and summarizes the research progress of nano-TiO2 in industrial wastewater, marine pollution, solid waste degradation, air purification and sterilization. At the same time, it is pointed out that the nano-TiO2 photocatalytic technology has not fully reached the practical application level, and the development trend of nano-TiO2 photocatalytic materials is prospected. Photocatalytic oxidation (PCO) using nanomaterials is a promising technology for removing pollutants, especially in deodorization, degradation of volatile organic compounds (VOCs) and sterilization. The mechanism of nanometer photocatalysis was reviewed in this paper. The influence factors including initial concentration of pollutants, reaction time, light intensity, humidity, surface area and catalyst activity were discussed. Furthermore, the application in photocatalytic removal of gas phase contaminants was summarized, and the future development of its application was proposed based on the existing problems.

Can the inhalation exposure of a specific worker in a cross-ventilated factory be evaluated by time- and spatial-averaged contaminant concentration?

Industry implies economic growth; however, outdoor and indoor air pollution generated by industrial activities represents a widespread problem for the environment and human beings. In terms of human health, indoor air quality assessment has become essential in a society where people spend most of their time in indoor dwellings, as in the case of industry workers. Because indoor air quality is strongly affected by the outdoor environment, especially under natural ventilation conditions (e.g., cross-ventilation), a comprehensive analysis that includes outdoor atmospheric-urban environment is needed to reproduce realistic scenarios. In this context, computational fluid dynamics (CFD) is a useful tool. To perform a precise analysis of the inhalation exposure of factory workers to potential gas-phase contaminants in the working environment (i.e., inhaled dose of contaminants and potential effects), the human body and respiratory tract need to be integrated in the analysis. Therefore, in this study, we performed an integrated occupational inhalation exposure/toxicology assessment in a factory building that applies a computer simulated person (CSP), a virtual human respiratory tract and integrated physiologically-based toxicokinetic (PBTK) model to predict tissue dosimetry distribution. Outdoor airflow variation was transported into the enclosure through an hourly change in wind pressure coefficient to calculate transient ventilation rate and indoor contaminant concentration between 08:00 and 17:00 h. Thereafter, the time-averaged contaminant concentration calculated at the nares of the human body was employed in a steady state calculation of airflow and contaminant distribution inside the virtual respiratory tract. Subsequently, we predicted adsorbed contaminant in the first layer of tissue of the human airways; highest adsorption took place in the nasal cavity. Finally, based on the results of the comprehensive coupled numerical analysis performed using the CFD-CSP-PBTK model, we quantitatively discussed differences between the inhalation exposure concentration and representative contaminant concentration in the factory space (e.g., time and volume-averaged concentration).

Conventional bioprocesses for the removal of gas-phase contaminants

Conventional bioprocesses for the removal of gas-phase contaminants

Effects of temperature and equivalence ratio on mass balance and energy analysis in loblolly pine oxygen gasification

AbstractThe purpose of this study was to evaluate the effects of temperature and equivalence ratios (ERs) on the distribution of products (primary gases carbon monoxide [CO], H2, CH4, CO2), gas phase contaminants (tar, NH3, HCN, H2S, HCl), char, carbon, and inorganics), and energy flows on an oxygen‐blown bubbling fluidized bed gasifier system using loblolly pine. The goal and value of this study was to provide quantitative and qualitative performance analysis and data for process engineering and optimization of these fledgling biomass conversion systems. As temperature and ER increased, mass balance closures also increased from 94.73% to 96.72% for temperature and 89.82–96.93% for ER. In addition, the carbon closures ranged from 80.77% to 92.29% and from 79.09% to 87.13% as temperature and ER increased, respectively. Carbon conversion efficiency to gas product ranged from 72.26% to 84.32% as temperature increased and from 72.26% to 84.66% as ER increased. Carbon flow analysis showed that the char product streams retained 10.26–6.94% and 8.82–2.13% of the carbon fed to the gasifier as temperature and ER increased, respectively. The carbon content in the liquid condensate was minimal compared to the carbon in other product streams and accounted for less than 0.1% of the carbon input to the gasifier at all conditions. The cold and hot gas efficiencies increased from 56.12% to 67.45% and from 67.51% to 83.83% as temperature increased due to higher production of CO and hydrogen (H2). In contrast, cold and hot gas efficiencies decreased from 63.85% to 52.84% and from 78.06% to 73.00% as ER increased, respectively, due to enhanced oxidation of gas products resulting in a net decrease in heating value.

PAH emissions from coal combustion and waste incineration

The characteristics of PAHs that are emitted by a municipal waste incinerator (MWI) and coal-fired power plant are examined via intensive sampling. Results of flue gas sampling reveal the potential for PAH formation within the selective catalytic reduction (SCR) system of a coal-fired power plant. In the large-scale MWI, the removal efficiency of PAHs achieved with the pilot-scaled catalytic filter (CF) exceeds that achieved by activated carbon injection with a bag filter (ACI+BF) owing to the effective destruction of gas-phase contaminants by a catalyst. A significantly lower PAH concentration (1640ng/g) was measured in fly ash from a CF module than from an ACI+BF system (5650ng/g). Replacing the ACI+BF system with CF technology would significantly reduce the discharge factor (including emission and fly ash) of PAHs from 251.6 to 77.8mg/ton-waste. The emission factors of PAHs that are obtained using ACI+BF and the CF system in the MWI are 8.05 and 7.13mg/ton, respectively. However, the emission factor of MWI is significantly higher than that of coal-fired power plant (1.56mg/ton). From the perspective of total environmental management to reduce PAH emissions, replacing the original ACI+BF process with a CF system is expected to reduce environmental impact thereof.

Concurrence of aqueous and gas phase contamination of groundwater in the Wattenberg oil and gas field of northern Colorado

The potential impact of rapid development of unconventional oil and natural gas resources using hydraulic fracturing and horizontal drilling on regional groundwater quality has received significant attention. Major concerns are methane or oil/gas related hydrocarbon (such as TPHs, BTEX including benzene, toluene, ethybenzene and xylene) leaks into the aquifer due to the failure of casing and/or stray gas migration. Previously, we investigated the relationship between oil and gas activity and dissolved methane concentration in a drinking water aquifer with the major finding being the presence of thermogenic methane contamination, but did not find detectable concentrations of TPHs or BTEX. To understand if aqueous and gas phases from the producing formation were transported concurrently to drinking water aquifers without the presence of oil/gas related hydrocarbons, the ionic composition of three water groups was studied: (1) uncontaminated deep confined aquifer, (2) suspected contaminated groundwater - deep confined aquifer containing thermogenic methane, and (3) produced water from nearby oil and gas wells that would represent aqueous phase contaminants. On the basis of quantitative and spatial analysis, we identified that the “thermogenic methane contaminated” groundwater did not have similarities to produced water in terms of ionic character (e.g. Cl/TDS ratio), but rather to the “uncontaminated” groundwater. The analysis indicates that aquifer wells with demonstrated gas phase contamination have not been contacted by an aqueous phase from oil and gas operations according to the methodology we use in this study and the current groundwater quality data from COGCC. However, the research does not prove conclusively that this the case. The results may provide insight on contamination mechanisms since improperly sealed well casing may result in stray gas but not aqueous phase transport.

Respiratory Protection for Firefighters— Evaluation of CBRN Canisters for Use During Overhaul

In the United States, there are approximately 366,600 structural fires each year. After visible flames are extinguished, firefighters begin the overhaul stage of firefighting to smother remaining hot spots and initiate investigations. Typically during overhaul significant ambient concentrations of chemical contaminants remain. However, previous research suggests that the use of air purifying respirators (APR) fitted with chemical, biological, radiological, and nuclear (CBRN) canisters may reduce occupational respiratory exposures. This pilot study used large-scale prescribed burns of representative structural materials to perform simultaneous, side-by-side, filtering and service-life evaluations of commercially available CBRN filters. Three types of CBRN canisters and one cartridge were challenged in repetitive post live-fire overhaul exposure tests using a sampling manifold apparatus. At a flow rate of 80L/min, nine tests were conducted in the breathing zone for three different exposure durations (0–15 min, 0–30 min, and 0–60 min). Fifty different chemicals were identified for evaluation and results indicate that 21 of the 50 chemicals tested were in the air of the overhaul environment. Respirable particles and formaldehyde were consistently present above the American Conference of Governmental Industrial Hygienists (ACGIH®) recommended exposure level (REL) and threshold limit ceiling value (TLVc), respectively. Each filter effectively reduced concentrations for respirable particulates below the maximum recommended level. Formaldehyde was reduced, but not consistently filtered below the TLVc. These results were consistent across all exposure durations. This study indicates that, regardless of brand, CBRN filters provide protection from the vast majority of particle and gas-phase contaminants. However, due to formaldehyde breakthrough, CBRN filters do not provide complete protection during firefighter overhaul.

Low temperature entrained flow pyrolysis and gasification of a Victorian brown coal

Abstract The entrained flow gasification of Victorian brown coals is of interest for its potential use as a syngas feedstock in established commercial processes. To determine the applicability of entrained flow gasification to a Victorian brown coal, and to establish the scope for further investigation, coal pyrolysis and char gasification trials were conducted using a vertical entrained flow reactor. Pyrolysis between 800 and 1000 °C resulted in high surface area char, and tar production decreased with increasing temperature. Char conversion and syngas yield increased with increasing gasification temperature. Pyrolysis tars and contaminants in the syngas were also evaluated to determine their potential impact on the industrial process. The concept of entrained flow gasification of Victorian brown coals was shown to be operationally sound, with minimal gas and liquid phase contaminants. However, the temperature and residence times chosen for this study were insufficient to achieve complete conversion of the fuel.

Evaluation of Gas‐Phase Filter Performance for a Gas Mixture

Adsorption‐based granular activated carbon (GAC) filter is one of the common techniques for removing gas phase contaminants. However, a large group of gas phase contaminants is present in indoor environment and limited studies have been carried out to investigate the impact of contaminants type, their mixture and indoor air humidity on the GAC performance. This paper reports the outcomes of a series of experimental work which was carried out on a full‐scale system to study the impact of gas phase contaminant type (toluene, n‐hexane, and methyl ethyl ketone (MEK)), their mixture, and indoor air relative humidity (RH) level on the performance of GAC filter. It was observed that the GAC filter performed well in removing toluene in both scenarios (single and mixture) due to its high molecular weight, boiling point, and polarizability to ion formation with the GAC, followed by n‐hexane and MEK. It was also noted that the GAC filter did not perform well in removing MEK due to its weak attractive forces with GAC as compare to n‐hexane and toluene. Among the different physical properties of indoor contaminant, removal performance and service life of the tested GAC filter were positively correlated to the contaminant molecular weight. In addition, the lower dipole moment and interaction energy made the adverse effects of indoor air RH on n‐hexane more visible than toluene and MEK. Finally, a significant difference was observed between quantification indexes of the filter in removing indoor air contaminants as a single gas and as a mixture gas. The removal efficiency of GAC filter for the mixture was significantly reduced compared to those for the single gases due to the presence of other compounds in gas mixture competing for the same free space on carbon media.

Life-Cycle Inventory and Impact Evaluation of Mining Municipal Solid Waste Landfills

Recent research and policy directives have emerged with a focus on sustainable management of waste materials, and the mining of old landfills represents an opportunity to meet sustainability goals by reducing the release of liquid- and gas-phase contaminants into the environment, recovering land for more productive use, and recovering energy from the landfilled materials. The emissions associated with the landfill mining process (waste excavation, screening, and on-site transportation) were inventoried on the basis of diesel fuel consumption data from two full-scale mining projects (1.3-1.5 L/in-place m(3) of landfill space mined) and unit emissions (mass per liter of diesel consumption) from heavy equipment typically deployed for mining landfills. An analytical framework was developed and used in an assessment of the life-cycle environmental impacts of a few end-use management options for materials deposited and mined from an unlined landfill. The results showed that substantial greenhouse gas emission reductions can be realized in both the waste relocation and materials and energy recovery scenarios compared to a "do nothing" case. The recovery of metal components from landfilled waste was found to have the greatest benefit across nearly all impact categories evaluated, while emissions associated with heavy equipment to mine the waste itself were found to be negligible compared to the benefits that mining provided.

Can Soil Gas VOCs be Related to Groundwater Plumes Based on Their Isotope Signature?

The isotope evolution of tetrachloroethene (PCE) during its transport from groundwater toward the soil surface was investigated using laboratory studies and numerical modeling. During air-water partitioning, carbon and chlorine isotope ratios evolved in opposite directions, with a normal isotope effect for chlorine (ε = -0.20‰) and an inverse effect for carbon (ε = +0.46‰). During the migration of PCE from groundwater to the unsaturated zone in a 2D laboratory system, small shifts of carbon and chlorine isotope ratios (+0.8‰) were observed across the capillary fringe. Numerical modeling showed that these shifts are due to isotope fractionation associated with air-water partitioning and gas-phase diffusion. Carbon and chlorine isotope profiles were constant throughout the unsaturated zone once a steady state was reached. However, depending on the thickness of the unsaturated zone and its lithology, depletion in heavy isotopes may occur with distance during the transient migration of contaminants. Additionally, variations of up to +1.5‰ were observed in the unsaturated zone for chlorine isotopes during water table fluctuations. However, at steady state, it is possible to link a groundwater plume to gas-phase contamination and/or to differentiate sources of contamination based on isotope ratios.

Evaluation of a new thermo-regenerative air cleaning device for reducing indoor exposure of multiple gas-phase contaminants

Background: There are many types of gas-phase contaminants indoors. Exposure to these compounds can cause some serious adverse health effects like allergy, cancer and leukemia etc. Adsorption technology is widely used to remove these pollutants for healthy indoor environment. However, the life span for indoor air pollutants is short, especially when the indoor concentrations of sub-ppbv level. Aims: This work aims to develop a new air cleaning device with thermo-regeneration for long term application. Methods: A thermo-regenerative air cleaning device is developed. Its removal performance for 8 kinds of indoor contaminants (acetaldehyde, ethanol, toluene, ethyl acetate etc.) is continuously validated in 30-round close-loop test and 6-round single-pass test. Each round spends 24 hours. After every round test, the device will be thermo-regenerative. The concentrations of contaminants were analyzed by GC-FID with the two-layer sorbent tubes (Tenax TA and Carbosieve III). The influence of moisture concentrations to the removal efficiency of pollutants is also detected. Results: Although the removal efficiency of pollutants is decreasing initially with the round times increasing, it keeps stable after 30-round test. The average removal efficiency of all pollutants is larger than 90% finally. Moisture is found to have great negative or passive impact to the adsorption effect, which seems linking to the hydrophilic or hydrophobic performance of pollutants. Conclusions: The results indicated that the developed air cleaning device can efficiently and continuously remove common indoor pollutants. It can be used to reduce the indoor exposure of multiple gas-phase contaminants simultaneously.

Monitoring atmospheric levels and deposition of dioxin-like pollutants in sub-alpine Northern Italy

The objective of this work was to assess the atmospheric occurrence, seasonal variations and deposition of dioxin-like pollutants (17 PCDD/Fs + 12 DL-PCBs) in sub-alpine northern Italy. A total of 108 weekly integrated samples (aerosol + gas phases) were collected during a 1-year period (2005–2006) at the Ispra EMEP site (Northern Italy, 45°49′N, 8°38′E). Atmospheric loadings into Lake Maggiore were also estimated by implementing a deposition model. ∑2,3,7,8-PCDD/F atmospheric total concentrations were dominated by the aerosol-bound fraction which ranged from 50 to 3080 (1–215 WHO98 TEQ) fg m−3. In contrast DL-PCB levels were dominated by the gas phase concentrations and varied from 1800 to 14800 (1–5 WHO98 TEQ) fg m−3. The aerosol and gas phase concentrations of PCDD/Fs and DL-PCBs exhibited a similar seasonality (higher values in winter time for aerosol-bound contaminants and lower concentrations for gas phase contaminants) in spite of their different environmental sources and properties. Estimated total atmospheric (dry + wet) depositional fluxes of dioxin-like pollutants in sub-alpine northern Italy were ∼0.2–∼9.5 ng m−2 d−1, with wet deposition dominating. Total atmospheric inputs (2,3,7,8-PCDD/Fs + DL-PCBs) into Lake Maggiore ranged from 14 to 304 g y−1. Higher environmental concentrations of dioxin-like pollutants in sub-alpine northern Italy are expected in the cold season and in rainy days due to a combined effect of stagnant atmospheric conditions (low winds), household wood burning in the region and higher pollutant loads via rainfall in winter.

BTEX decomposition by ozone in gaseous phase

Environment management is turning its efforts to control the air pollution. Nowadays, gas phase contaminants coming from different sources are becoming into the main cause of serious human illness. Particularly, benzene, toluene, ethylbenzene and xylene (BTEX) are getting more and more attention from the scientific community due the high level of volatilization showed by these compounds and their toxicity. Decomposition of these compounds using different treatments is requiring lots of new strategies based on novel options. In the present work the use of ozone was proposed as possible alternative treatment in the gaseous phase of VOC's liberated from water by stripping. This study deals with the decomposition by ozone in gaseous phase of model mixtures of BTEX stripped from water. The experiments were realized in a tubular reactor with fixed length (1.5 m length and diameter of 2.5 cm). The experiments were conducted in two stages: in the first one, organics was ventilated by oxygen flow to liberate BTEX to the gaseous phase; second stage deals with the liberated BTEX decomposition by ozone in the tubular reactor. Ozonation efficiency was determined measuring the VOC's concentration at the output of the tubular reactor. This concentration was compared to the concentration obtained at the input of the reactor. The obtained results confirm the possibility to use of ozone for the VOC's decomposition in gaseous phase. Also, the dynamic relationship between degradation and liberation was studied and characterized.

PEMFC contamination model: Foreign cation exchange with ionomer protons

A generic, transient fuel cell ohmic loss mathematical model was developed for the case of contaminants that ion exchange with ionomer protons. The model was derived using step changes in contaminant concentration, constant operating conditions and foreign cation transport via liquid water droplets. In addition, the effect of ionomer cations redistribution within the ionomer on thermodynamic, kinetic and mass transport losses and migration were neglected. Thus, a simpler, ideal, ohmic loss case is defined and is applicable to uncharged contaminant species and gas phase contaminants. The closed form solutions were validated using contamination data from a membrane exposed to NH3. The model needs to be validated against contamination and recovery data sets including an NH4+ contaminated membrane exposed to a water stream. A method is proposed to determine model parameters and relies on the prior knowledge of the initial ionomer resistivity. The model expands the number of previously derived cases. Most models in this inventory, derived with the assumption that the reactant is absent, lead to different dimensionless current vs. time behaviors similar to a fingerprint. These model characteristics facilitate contaminant mechanism identification. Separation between membrane and catalyst (electroinactive contaminant) contamination is conceivably possible using additional indicative cell resistance measurements. Contamination is predicted to be significantly more severe under low relative humidity conditions.