Diffusion Of Volatile Organic Compounds Research Articles

Role of molecular size of volatile organic compounds on their adsorption by KOH-activated micro-mesoporous carbon

KOH-activated carbon (KAC) with high surface area and abundant micropores are widely used in adsorbing volatile organic compounds (VOCs). Kinetic diameters (σ) of VOCs are an important factor controlling diffusion of VOCs into pores of adsorbent. Yet the influence of kinetic diameters of VOCs on their adsorption by KAC remains unclear. Here, we investigated the dynamic adsorption of VOCs with various kinetic diameters on a prepared KAC with high surface area of 3100 m2/g, pore volume of 2.08 cm3/g and average pore width (D) of 2.68 nm. Adsorption affinity was negatively correlated with size difference (D-σ), indicating that pore width of adsorbent should close to σ to obtain a strong interaction between VOCs and adsorbents. Amounts adsorbed were positively correlated with σ at low relative pressures (p/p0 < 0.01), and negatively correlated with σ at high relative pressures (p/p0 > 0.044). The above results suggest that larger molecules with higher affinities are preferentially adsorbed at low relative pressures, amounts adsorbed of smaller molecules are larger than that of bigger molecules at high relative pressures. This study provided new insights into adsorption mechanisms mediated by σ and the development of next generation adsorbents for efficient removal of VOCs.

Theoretical exploration of VOCs removal mechanism by carbon nanotubes through persulfate-based advanced oxidation processes: Adsorption and catalytic oxidation

Carbon-catalyzed persulfate activation for the removal of gaseous volatile organic compounds (VOCs) has not been reported yet, and the corresponding fundamental mechanisms of VOCs adsorption and the subsequent VOCs degradation remain controversial. In this work, theoretical chemistry calculations were carried out to explore the VOCs removal mechanism by the persulfate-based advanced oxidation processes (P-AOPs) for VOCs removal over single walled carbon nanotubes (SWCNT). This study provided detailed theoretical insights into the SWCNT/P-AOPs for VOCs treatment in terms of adsorption, activation, mineralization, and diffusion of VOCs or peroxymonosulfate (PMS). Various VOCs were found to be preferentially adsorbed onto SWCNT, and the adsorption strength of VOCs was found to be significantly dependent on their polarizability. On the other side, PMS adsorbed on SWCNT could be efficiently activated through accepting π electron in the sp2 carbon matrix of SWCNT rather than the electrons at dangling bonds to generate •OH radicals attributed to the strong interaction between PMS and SWCNT. Formaldehyde was then taken as an example to evaluate the catalytic degradation pathways via SWCNT/P-AOPs. Under the attack of •OH radicals, the ultrafast degradation pathway of formaldehyde with no byproduct CO was identified with ultralow reaction energy barrier and large energy release. In addition, factors affecting the adsorption of organic compounds were identified and the detailed PMS activation pathway was present directly in this work. Above all, this work extended the carbons/P-AOPs system to VOCs abatement and presented systematic evidences for the essential mechanisms associated with VOCs adsorption and PMS activation by SWCNT, and the corresponding removal pathway and mechanism were also understood.

Modeling the similarity and the potential of toluene and moisture buffering capacities of hemp concrete on IAQ and thermal comfort

Controlling and understanding indoor humidity and pollutants can help reduce the risk of health concerns. The experimental results suggested that there is a similarity relationship between water vapor and Volatile Organic Compounds (VOC) in diffusion through porous media. In this paper, the similarity between the moisture and pollutant transport and storage coefficients of porous building materials has been clearly established and explained. In addition, two similarity coefficients have been defined for VOC storage and diffusion to estimate the VOC properties from the moisture properties of the same material. A coupled hygric-pollutant (VOC) model which can be used to simulate VOC and hygric behavior of building materials under dynamic conditions is presented. The model which is implemented in the environment SPARK (Simulation Problem Analysis and Research Kernel) suited to complex problems using finite difference technique with an implicit scheme, has been validated with the experimental data. It is then applied to study the effect of toluene and moisture buffering capacities of a hemp concrete wall on indoor toluene concentration and relative humidity (RH). Hemp concrete was chosen in this study because it is an environmentally-friendly material that is used more and more in building construction. The toluene (TOL, selected VOC for this study) transport and storage properties obtained from hygrique properties of hemp concrete based on the assumption of the similarity between toluene and moisture transport have been modelled and investigated. At the room level, the results obtained show that taking into account the sorption capacity toward moisture and toluene has a significant effect on indoor RH and IAQ because hemp concrete contributes to dampen indoor RH and toluene variations. The numerical model presented is very useful for the building design optimization and can be used for a fast estimation of indoor pollution and hygrothermal conditions in building.

Self-assembly Cu2O nanowire arrays on Cu mesh: A solid-state, highly-efficient, and stable photocatalyst for toluene degradation under sunlight

Sunlight driven photocatalysis offers an effective and eco-friendly technology for volatile organic compounds (VOCs) removal. Three dimensional (3D) and oriented structure can facilitate efficient photon absorption and rapid diffusion of VOCs, which prevails over the powder-formed catalysts. Herein, free-standing and uniform p-type Cu2O nanowire (NW) arrays were obtained through heat treatment of Cu(OH)2 NWs, which were spontaneously grown from Cu mesh in air under room temperature for the first time. The as-prepared Cu2O NWs show excellent degradation performance in decomposing 30 ppm toluene (99.9 % within 120 min) and high stability (no decline after ten recycles). The toluene degradation was also conducted under the natural sunlight, demonstrating complete removal from 12:00 am to 15:00 pm. During photocatalysis, toluene is attacked by the photogenerated holes (h+) and hydroxyl radicals (·OH), and finally oxidized to nontoxic small molecules. The photocatalytic removing toluene with Cu2O NWs/Cu mesh has a promising application prospect owing to its low cost, high efficiency, stability, and convenient operation.

Atmospheric diffusion profiles and health risks of typical VOC: Numerical modelling study

Volatile organic compounds (VOC) are dominantly from industrial production. Comprehension of atmospheric diffusion of VOC is realistic to discharge reduction. Here, transport ranges of VOC were analyzed by aerodynamics modelling, and validated with on-site monitoring. By combining a terrain evolution model, spatiotemporal distributions of typical VOC, the impacts of wind speeds and directions in relation to topographical parameters were acquired. The model outputs show that the low elevation landscapes experience significant variation in concentration distributions of VOC when accompanied by strong shear flow regimes with non-uniform wind velocities. Case studies suffer 13.0% and 24.2% increases of VOC concentration ratio outside/inside industry park, with long-range transport of VOC indicated by dominances of lower wind speeds and higher humidity. High ratio, from atmospheric diffusion of VOC from industry park, poses great exposure risk to surrounding residents. The spatial map of time-specific health risks, proving VOC concentration accumulation enhancing risks of school-aged children than adults, was consequently produced from models. Overall, addressing the impact of regularities during VOC diffusion on occupational workers and residents will suggest a valuable reference for decision-making of emission-abatement strategies and awareness-raising health-risk interventions.

Behaviour of individual VOCs in indoor environments: How ventilation affects emission from materials

Indoor air quality is affected by both emissions of Volatile Organic Compounds (VOC) from materials and ventilation. The purpose of this paper is to provide a multi-scale analysis of the impact of ventilation on VOC emissions to highlight the individual behaviours of VOCs emitted from a wood particleboard. Emissions were studied in an experimental chamber by (i) assessing the effect of ventilation on emission rates and (ii) determining intrinsic parameters (Ki, C0,i, Di) describing the VOC mass transfer from the material to air. The overall assessment of the effect of ventilation indicated that the air change rate could significantly affect the behaviour of individual compounds. Typically, the formaldehyde emission rate increased from 214.6 to 274.2 μg.m−2.h−1 when air change rate varies from 2.5 to 5.5 h−1, whereas the air speed had no influence on emission rates for any VOC monitored. These results agree with the key emission parameters (partitioning and diffusion coefficients) which were higher for formaldehyde than those for other compounds. VOC diffusion related to VOC mass transfer from a material's surface to the surrounding air was the limiting step in VOC emission for the solid material studied, and should therefore be considered when developing ventilation strategies.

Three-dimensional geometry, pore parameter, and fractal characteristic analyses of medium-density fiberboard by X-ray tomography, coupling with scanning electron microscopy and mercury intrusion porosimetry

Pore structure parameters are significant for investigating the diffusion properties of volatile organic compounds from building materials. Traditional characterization methods could provide ether surface morphology or some pore parameters of the material, which could not comprehensively reflect the overall information. X-ray tomography, as an advanced nondestructive method, can not only characterize the three-dimensional structure characteristics but also comprehensively measure pore parameters of materials. This study applied X-ray tomography to systematically analyze the geometry and volatile organic compound emission paths of medium-density fiberboard. The three-dimensional structures of pores and materials were reconstructed respectively. The isolated pores and connective pores were extracted to indicate the pore connectivity, and skeletonization was simultaneously applied, allowing visualization of the volatile organic compound diffusion paths. The porosity was 54.67%, and 99.91% of the pores were connective pores. The tortuosity was 2.07, and the fractal dimension was 2.605, indicating the heterogeneity and self-similarity of pore structures. Scanning electron microscopy was used to characterize the two-dimensional morphology of the material, and mercury intrusion porosimetry was applied to analyze the pore parameters. The results were consistent with that of X-ray tomography, and their coupling with X-ray tomography could comprehensively characterize the structures and parameters of indoor building materials, which could contribute significantly to future research on volatile organic compound emission mechanisms and building physics.

Measurements and modeling of absorptive partitioning of volatile organic compounds to painted surfaces.

Partitioning to surfaces is an important sink for volatile organic compounds (VOCs) indoors, but the mechanisms are not well understood or quantified. Here, a mass spectrometer was coupled to a portable surface reactor and a flow tube to measure partitioning of VOCs into paint films coated onto glass or wallboard, and their subsequent diffusion. A model was developed to extract values of the effective absorbing organic mass concentration of the film, Cw , which is a measure of absorption capacity, and VOC diffusion coefficients, Df , from VOC time profiles measured during film passivation and depassivation. Values of Cw agreed well with the value estimated from the paint film mass and flow tube air volume, and Df values (also measured using attenuated total reflectance-Fourier transform infrared spectroscopy) correlated well with VOC vapor saturation concentrations, C*, estimated using a group contribution method. The value of these relationships for estimating key parameters that control VOC partitioning into paint and the fate of VOCs indoors was demonstrated using a house model, which indicated that >50% of VOCs with C* ≤108 μg/m3 (C* of octane, hexanone, and propanol) that contacted a paint film of typical thickness fully permeated the film regardless of emission duration.

A spatial fractional diffusion model for predicting the characteristics of VOCs emission in porous dry building material

Volatile organic compounds (VOCs) concentrations of dry building materials can significantly affect the quality of indoor air. In this paper, a spatial fractional diffusion model is established by introducing fractional Fick’s law, based on the fact that the pore structure of porous building materials has a strongly impact on VOCs diffusion. Furthermore, the areal porosity of the material is drawn into the convection mass transfer equation. The relevant parameters are estimated by a kind of optimization algorithm. The fractional nonlinear equations are tackled by the finite difference method combined with L2-algorithm. Results indicate that spatial fractional diffusion model agrees better with the experimental data than Deng and Kim’s model. The spatial fractional diffusion model is used to describe the formaldehyde concentration in the particleboard according to the experimental data. Taking formaldehyde as a common substance, the influences of physical parameters on VOCs diffusion are predicted by this model. The results of numerical simulation demonstrate that the diffusion is consistent with the actual situation.

Models for assessment of volatile organic compound diffusivities in leather or leather imitates by mercury intrusion porosimetry test

Recent studies have been conducted on the characteristics of volatile organic compound emissions; most of them are focused on wood-based building materials, scarcely mentioned about leather or leather imitates. The volatile organic compound emissions of these products may cause poor indoor (vehicle cabins included) air quality. This article takes formaldehyde as an example to study its diffusion in leather. The porous structure of leather was characterized by carrying out mercury intrusion porosimetry test. The formaldehyde diffusivities in leather was assessed by Blondeau et al.’s, Ataka et al.’s, and Xiong et al.’s models which represent parallel, equivalent, and series interconnection of pores, respectively, and validated through independent liquid inner tube diffusion film emission experiments. The results demonstrated that the fractal dimension of leather is 2.19, which indicated it is a porous medium with self-similar pore structure. Most of the pores in leather were macro pores with average diameter 16.56 μm which contributed to 95.9% of whole porosity and the meso pore with average diameter 0.60 μm which contributed to 4.1%. As far as the liquid inner tube diffusion film emission experiment shows, the Xiong model agrees much better with the experimental results than the other two. The two kinds of pores were considered to be serially connected. It is useful for predicting volatile organic compounds diffusion coefficient in a short time and can be applied to the design and development of low volatile organic compound emission leather or leather imitates within further research.

An Investigation of Plume Response to Soil Vapor Extraction and Hypothetical Drum Failure

Core Ideas Soil vapor extraction (SVE) wells are an effective interim remediation technique. Flow and transport modeling assists in evaluation of vapor plume behavior. Plume simulations assuming drum failure and SVE provide a framework for remediation planning. A small borehole subset could be monitored for detection of VOC releases due to drum failure. Soil vapor extraction (SVE) has been used at sites across the Department of Energy complex, including sites where legacy subsurface wastes represent a potential source of groundwater contamination. At Los Alamos National Laboratory (LANL), leakage from waste drums buried at an inactive chemical waste site has created a subsurface vapor plume of volatile organic compounds (VOCs). Soil vapor extraction operation in 2015 and rebound testing through 2017 were successful in reducing the plume's mass and mitigating VOC migration toward the water table. However, the possibility that waste drums could fail and release VOCs could pose a challenge in the future. To explore the impacts of drum failure, as well as the capabilities of SVE remediation, we simulated hypothetical contaminant release scenarios and subsequent SVE remediation. Three‐dimensional subsurface VOC behavior, including advection, diffusion, and plume interactions with topography, were simulated using the porous flow simulator Finite Element Heat and Mass Transfer. Simulations of future site conditions have allowed identification of “sentry” boreholes that can be monitored for early detection in case of drum failure. Sentry boreholes can also be used to set concentration thresholds above which SVE should be initiated. For the LANL site, simulations show that SVE can be started 3 yr following drum failure and remain a viable remediation tool. More broadly, the principles outlined in this work can be used to support remediation planning at other subsurface waste sites. Predictive models of future releases can be analyzed to set concentration threshold values, guide selection of sentry boreholes, and increase operational efficiency.

Sources and abatement mechanisms of VOCs in southern China

Volatile organic compounds (VOCs) have an important influence on the formation of photochemical smog and secondary organic aerosols in the atmosphere. In this paper, we investigated 104 VOCs in Heshan from 22 October to 22 November 2014 to identify the sources and abatement mechanisms of VOCs in southern China. Weather conditions, species correlations, daytime and nighttime abatement mechanisms, secondary pollutant transformations, air-mass origins and source apportionments were studied. During the observation period, the average concentration of VOCs in the atmosphere of Heshan was 61.0 ± 35.5 ppbv, and the wind speed played a pivotal role in the diffusion and dilution of VOCs. The study on the rates of OH, O3 and NO3 radicals found that alkenes, aromatics, hydrocarbons and carbonyl compounds were the most active volatile organic compounds in Heshan. For alkanes, alkynes, and aromatics, removal is determined by their reactions with OH radicals. For highly reactive alkenes and styrene, nighttime removal via O3 and NO3 radicals was also significant. The backward-trajectory cluster analysis of air masses indicated that pollution mainly derived from the east-northeast. The paint solvent usage, paint solvent usage + liquefied petroleum gas (LPG) usage, biomass burning, coal burning + industrial combustion sources, gasoline vehicle exhaust, diesel vehicle exhaust, industrial sources, and fuel evaporation (gasoline) contributed 11%, 22%, 13%, 17%, 12%, 8%, 11%, and 6% to VOCs during the observation period, respectively.

Indoor Volatile organic Compounds Diffusion Model of Building Materials Based on Cloud Computing

Based on the cloud computing platform, this paper constructs an analytical model for the indoor diffusion process of volatile organic compounds (VOCs) in building decoration materials. The model considers key parameters such as diffusion concentration, diffusion coefficient, and closed chamber background value, and validates the model through practical examples. The results show that the VOC diffusion law obtained by the proposed model and the numerical simulation calculation model is basically the same, and the calculation time of the proposed model is shorter. The VOCs in indoor building materials mainly undergo two stages of diffusion mass transfer and convective mass transfer, and finally diffuse into the space of the closed chamber. In the early and middle stages of VOC diffusion, the environmental concentration in the closed chamber changes drastically. In the late stage of diffusion, in the closed chamber, the environmental concentration gradually reaches equilibrium, and the mass transfer characteristics of the VOC are basically unaffected by the area of the closed chamber and the air flow rate.

Volatile organic Compounds Diffusion Model of Atmospheric Pollutants in Central Urban Area Based on GIS

Atmospheric pollutant VOCs are negative products brought about by economic development and urbanization. They are mainly produced by chemical production and transportation industries, which have seriously affected people's daily life. GIS has superior spatial analysis and data management functions. This paper builds a diffusion model of urban atmospheric pollutant VOCs based on GIS technology, provides intuitive, scientific and effective data for assisting atmospheric pollution emergency work, and studies and analyzes the atmospheric pollution diffusion simulation in Central Urban Area of Changsha City. The results show that GIS has a wide range of applications in the atmosphere, including data preprocessing, secondary development of models, final data processing, and display output of computing results. Map Objects is introduced to confirm the feasibility and necessity of integrating atmospheric pollution diffusion research with GIS. The study on VOCS diffusion model of atmospheric pollutants in central urban area based on GIS finds that the atmospheric pollution characteristics and pollution sources distribution of VOCs in the central urban area of Changsha City are closely related to the environment of the built-up area.

Development of Solid Ceramic Dosimeters for the Time-Integrative Passive Sampling of Volatile Organic Compounds in Waters.

Time-integrative passive sampling of volatile organic compounds (VOCs) in water can now be accomplished using a solid ceramic dosimeter. A nonporous ceramic, which excludes the permeation of water, allowing only gas-phase diffusion of VOCs into the resin inside the dosimeter, effectively captured the VOCs. The mass accumulation of 11 VOCs linearly increased with time over a wide range of aqueous-phase concentrations (16.9 to 1100 μg L-1), and the linearity was dependent upon the Henry's constant (H). The average diffusivity of the VOCs in the solid ceramic was 1.46 × 10-10 m2 s-1 at 25 °C, which was 4 orders of magnitude lower than that in air (8.09 × 10-6 m2 s-1). This value was 60% greater than that in the water-permeable porous ceramic (0.92 × 10-10 m2 s-1), suggesting that its mass accumulation could be more effective than that of porous ceramic dosimeters. The mass accumulation of the VOCs in the solid ceramic dosimeter increased in the presence of salt (≥0.1 M) and with increasing temperature (4 to 40 °C) but varied only slightly with dissolved organic matter concentration. The solid ceramic dosimeter was suitable for the field testing and measurement of time-weighted average concentrations of VOC-contaminated waters.

Evaluation of a four-component composite landfill liner system

The performance of four different municipal solid waste landfill liner systems common in the United States, that is, USEPA Subtitle D prescribed composite liner system, composite liner system consisting of a geomembrane (GM) overlying a geosynthetic clay liner (GCL), Wisconsin NR500 liner system, and a proposed four-component composite liner system that is a combination of the GCL composite liner and Subtitle D liner system (with a 61-cm or 91·5-cm thick low hydraulic conductivity compacted soil), were evaluated in terms of leakage rate, solute mass flux, and cumulative solute mass transport. Leakage rates through circular and non-circular GM defects were analysed using both analytical and numerical methods. For the mass flux evaluation, solute transport analyses using GM defects and diffusion of volatile organic compounds through intact liners were conducted using one- and three-dimensional numerical models. Cadmium and toluene were used as typical inorganic and organic substances, respectively, in the analyses. The comparison shows that for the limited set of conditions considered, the four-component composite liner system outperforms the Subtitle D and Wisconsin NR500 liner systems based on leakage rate and mass flux and provides similar results to the GM/GCL liner system. Based on the analyses presented herein the four-component liner system is a viable choice for a protective Subtitle D composite liner system and provides some added protection to the GCL.

Potential solution to pollution of groundwater by diffusion of volatile organic compounds through the primary HDPE geomembrane in composite lining systems of landfills

Waste in a landfill is exposed to the chemicals and heat generated over time, producing harmful fluids in the form of leachate or landfill gas that migrate from the landfill towards the liner or capping, and include organic contaminants. The high-density polyethylene (HDPE) geomembrane (GM) component of the landfill liner is often believed to be the primary barrier to contaminant transport, but volatile organic compounds (VOCs) diffuse through geomembranes at appreciable rates. The aim of this study was to obtain reliable data on the reduction in diffusion of VOCs through the HDPE GM component in the composite liner systems of landfills by extracting air through the leakage detection layer or drainage layer of the composite liner. It was shown that introducing a flow of air through a pervious zone adjacent to the GM layer in a landfill liner would significantly reduce the concentrations of VOCs in the groundwater beneath landfills and waste containment facilities.

First- and second-hand smoke dispersion analysis from e-cigarettes using a computer-simulated person with a respiratory tract model

The purpose of this study was to investigate, in the human respiratory tract, the flow patterns and adsorption flux (deposition flux) distributions of volatile organic compounds (VOCs) generated by the use of electronic cigarettes (e-cigarettes) through the application of a three-dimensional computational fluid dynamics (CFD) analysis. Two types of human respiratory tract models, which give detailed respiratory tract geometries were reproduced in this study using computed tomography data, for the CFD analysis of inhalation exposure. Complicated flow patterns, nonuniform distributions of VOC concentrations, and heterogeneous adsorption flux distributions were determined within the human respiratory tract models, and individual specificity was confirmed. The CFD simulation results of adsorption flux distributions on the epithelium tissue surfaces of airways denoted the probability distributions of inhalation exposure in respiratory tracts, and high adsorption flux sites representing ‘hot spots’ were delineated for tissue doses of VOCs generated from smoking e-cigarettes. Furthermore, dispersion and diffusion of VOCs in an indoor environment due to exhalation of the vapour phase of e-cigarette emissions were analysed by using a computer-simulated person with a numerical respiratory tract model through an integrated and contiguous analysis of inhalation and exhalation modes during e-cigarette smoking.

An analytical model for vapor‐phase volatile organic compound diffusion through landfill composite covers

SummaryOne‐dimensional mathematical models for vapor‐phase volatile organic compound (VOC) diffusion through composite cover barriers are presented. An analytical solution to the model was obtained by the method of separation of variables. The results obtained by the proposed solution agree well with those obtained by a numerical analysis. Based on the proposed analytical model, the VOC breakthrough curves of five different composite covers are compared. The effects of degree of saturation of geosynthetic clay liner (GCL) or compacted clay liner (CCL) on VOC migration in the composite covers are then presented. Results show that the composite cover barriers provide much better diffusion barriers for VOC than the single CCL. The top surface steady‐state flux for a composite barrier, consisting of a 1.5 mm geomembrane (GM) and a 20 cm CCL, can be 8.3 times lower than that for a 30 cm CCL. The surface steady‐state flux for the case with (1.5 mm GM + 6 mm GCL) was found to be 2.3 times lower than that for the case with (1.5 mm GM + 20 cm CCL). The degree of saturation Sr of the CCL has a great influence on VOC migration in composite covers when Sr is larger than 0.5. The steady‐state flux at the surface of GM for the case with Sr = 0.7 can be 1.8 times lower than that for the case with Sr = 0.2. The proposed analytical model is relatively simple and can be used for verification of complicated numerical models, analysis of experimental data and performance assessment of composite cover barriers. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Evaluation of a horizontal permeable reactive barrier for preventing upward diffusion of volatile organic compounds through the unsaturated zone

Permeable reactive barriers are commonly used to treat contaminant plumes in the saturated zone. However, no known applications of horizontal permeable reactive barriers (HPRBs) exist for oxidizing volatile organic compounds (VOCs) in the unsaturated zone. In this study, laboratory column experiments were carried out to investigate the ability of a HPRB containing solid potassium permanganate, to oxidize the vapors of trichloroethylene (TCE), toluene, and ethanol migrating upward from a contaminated saturated zone. Results revealed that an increase in initial water saturation and HPRB thickness strongly affected the removal efficiency of the HPRB. Installing the HPRB relatively close to the water table was more effective due to the high background water content and enhanced diffusion of protons and/or hydroxides away from the HPRB. Inserting the HPRB far above the water table caused rapid changes in pH within the HPRB, leading to lower oxidation rates. The pH effects were included in a reactive transport model, which successfully simulated the TCE and toluene experimental observations. Simulations for ethanol were not affected by pH due to condensation of water during ethanol oxidation, which caused some dilution in the HRPB.