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.
•The impact of ventilation on VOC emission is analysed using different approaches.•A wood particleboard into a 128-L ventilated chamber is considered.•Emission parameters (K, D, C0) of each individual VOC are measured.•The singular behaviour of formaldehyde regarding ventilation is explained.•Ventilation strategies can be updated according to these results.
The 2020 plasma catalysis roadmap Bogaerts, Annemie; Tu, Xin; Whitehead, J Christopher ...
Journal of physics. D, Applied physics,
10/2020, Letnik:
53, Številka:
44
Journal Article
Recenzirano
Odprti dostop
Plasma catalysis is gaining increasing interest for various gas conversion applications, such as CO2 conversion into value-added chemicals and fuels, CH4 activation into hydrogen, higher hydrocarbons ...or oxygenates, and NH3 synthesis. Other applications are already more established, such as for air pollution control, e.g. volatile organic compound remediation, particulate matter and NOx removal. In addition, plasma is also very promising for catalyst synthesis and treatment. Plasma catalysis clearly has benefits over 'conventional' catalysis, as outlined in the Introduction. However, a better insight into the underlying physical and chemical processes is crucial. This can be obtained by experiments applying diagnostics, studying both the chemical processes at the catalyst surface and the physicochemical mechanisms of plasma-catalyst interactions, as well as by computer modeling. The key challenge is to design cost-effective, highly active and stable catalysts tailored to the plasma environment. Therefore, insight from thermal catalysis as well as electro- and photocatalysis is crucial. All these aspects are covered in this Roadmap paper, written by specialists in their field, presenting the state-of-the-art, the current and future challenges, as well as the advances in science and technology needed to meet these challenges.
Essential-oils have attracted increasing interest due to their performance as inhibitors of the metabolic functions of microorganisms. They are widely promoted as easy-to-use compounds to improve ...indoor air quality and are associated with purifying actions. This study aims to assess the emissions of molecules contained in essential-oils in confined environments by employing different diffusion mechanisms under realistic conditions. Terpenes and carbonyl compounds are the typical identified and quantified compounds emitted from the tea tree essential-oil. Contrasted concentration levels and kinetic parameters are evidenced depending on the mechanism of diffusion, and the concentration levels can exceed the recommended critical exposure level by one order of magnitude. Additionally, the relative contributions of individual terpenes in the gas phase vary throughout the diffusion process for all the investigated diffusers. To assess the duration of the impact of essential-oil diffusion on indoor air quality, the mass emission rates of individual terpenes are estimated. This study shows that, depending on the diffusion mechanism, the impact of essential-oil diffusion in confined environments varies from 5 h to 60 days. The proposed experimental approach and the results provided offer the first insights into the definition of risk scenarios and human exposure to essential-oils in indoor environments.
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•Realistic quantitative determination of terpenoid VOC emissions from essential oils.•Comparison of the contributions of continuous vs. transient diffusers of essential oils.•Investigation of the dependence of the nature of emitted terpenes on diffusion time.•Environmental evaluation of the impact of essential oil diffusion on indoor air quality.
The interactions between the emission of Volatile Organic Compounds (VOCs) and airflow play a key role in determining indoor pollutant concentrations. In the framework of Indoor Air Quality (IAQ) ...prediction, numerical models based on fluid dynamics are useful tools to address typical cases and then make decisions to improve both public and occupational health. This requires an accurate description of VOC emission processes from building materials, products and furniture, taking into account the diffusion of VOCs into these materials instead of using constant surface emission rates. A predictive model combining Computational Fluid Dynamics (CFD) for airflow and kinetics modelling for VOC emissions is described. The validation of airflow and VOC transfer models is carried out by comparing experimental and simulation results into a 128 L ventilated experimental chamber.Our results show that the Reynolds-Averaged Navier Stokes (RANS) approach, together with a standard k-ω turbulence model, provide good agreement between numerical and experimental airflows regarding both air velocity and age of air profiles. The overall VOC dynamics is also reproduced by numerical simulation for the eight VOCs monitored. The predicted absolute VOC concentrations are in agreement with experimental data for acetone, formaldehyde, hexanal and terpenes. However, numerical simulations underestimate the concentration of pentanal, propanal, butanal, acetaldehyde, which is discussed in terms of representativeness of emission parameters. Our results highlight that CFD simulations combined with VOC emission kinetics modelling is a promising tool for IAQ prediction, but it requires further investigation to fully understand the observed behaviour for some VOCs. This finally demonstrates the crucial need of tracking various VOCs simultaneously in the framework of assessing an IAQ prediction model.
Essential oils are frequently used as natural fragrances in housecleaning products and air fresheners marketed as
green
and
healthy
. However, these substances are volatile and reactive chemical ...species. This review focuses on the impact of essential oil-based household products on indoor air quality. First, housecleaning products containing essential oils are explored in terms of composition and existing regulations. Specific insight is provided regarding terpenes in fragranced housecleaning products, air fresheners, and pure essential oils. Second, experimental methodologies for terpene monitoring, from sampling to experimental chambers and analytical methods, are addressed, emphasizing the experimental issues in monitoring terpenes in indoor air. Third, the temporal dynamics of terpene emissions reported in the literature are discussed. Despite experimental discrepancies, essential oil-based products are significant sources of terpenes in indoor air, inducing a high exposure of occupants to terpenes. Finally, the fate of terpenes is explored from sorptive and reactive points of view. In addition to terpene deposition on surfaces, indoor oxidants may induce homogeneous and heterogeneous reactions, resulting in secondary pollutants, such as formaldehyde and secondary organic aerosols. Overall, essential oil-based products can negatively impact indoor air quality; therefore, standard protocols and real-scale approaches are needed to explore the indoor physics and chemistry of terpenes, from emissions to reactivity.
Inorganic construction materials are chiefly envisaged as structural materials. However, they provide unexplored interfaces with characteristic surface chemistry to interact with indoor gases. This ...work proposes for the first time an insight on uptake abilities of lime-cement-plaster toward indoor pollutant. Because of toxicity and regulation policies, formaldehyde is selected as representative indoor pollutant. This work explores gas-material interaction to elucidate fate of formaldehyde onto lime-cement-plaster and addresses air quality impact. Uptake and fate of formaldehyde onto plaster is addressed using Field and Laboratory Emission Cell coupled with SIFT Mass Spectrometer. The experimental sequence is continuously deployed on 90 days to address realistic and long-term behaviour of formaldehyde uptake. Experimental approach evidences that from 65 to 77% of formaldehyde inlet concentration is continuously taken up on plaster samples throughout experimental sequence. Concomitantly, methanol is observed showing the reactivity of formaldehyde uptake on this material-class. Diffuse Reflectance Infrared Spectroscopy evidences that formaldehyde undergoes heterogeneous Cannizzaro reaction on the plaster surface. This surface reaction proceeds with adsorbed formaldehyde, even in the absence of gaseous pollutant supply. The quantitative balance of the disproportionation process is proposed along the experimental sequence to clarify the fate of formaldehyde encompassing gaseous and adsorbed-phase. The evidenced surface process can impact formaldehyde budget in indoor air, thus relevant parameters are determined to allow further implementation of this reactive contribution to indoor air quality models. This work settles perspectives for passive mitigation of indoor formaldehyde, and points at the need to address reaction products for their indoor air quality impact.
•Quantification of formaldehyde uptake on cement plaster under indoor conditions.•Long-term determination of the fate of taken up formaldehyde: 90-day experiment.•Evidence for heterogeneous Cannizzaro reactivity of formaldehyde on plaster.•Evaluation of the indoor air impact of formaldehyde processing by plaster.
The experimental investigation of heterogeneous atmospheric processes involving mineral aerosols is extensively performed in the literature using proxy materials. In this work we questioned the ...validity of using proxies such as Fe2O3, FeOOH, Al2O3, MgO, CaO, TiO2, MnO2, SiO2, and CaCO3 to represent the behavior of complex mixtures of minerals, such as natural desert and volcanic dusts. Five volcanic dusts and three desert dusts were compared to a number of metal oxides, commonly used in the literature to mimic the behavior of desert dusts in the ability to form sulfites and sulfates on the surface exposed to SO2 gas. First, all samples were aged at room temperature, atmospheric pressure, under controlled experimental conditions of 175 ppm SO2 for 1 h under 30% of relative humidity. Second, they were extracted with 1% formalin and analyzed by High-Performance Liquid Chromatography (HPLC) to quantify and compare the amount of sulfites and sulfates formed on their surfaces. It was evidenced that under the experimental conditions of this study neither one selected pure oxide nor a mixture of oxides can adequately typify the behavior of complex mixtures of natural minerals. Therefore, to evaluate the real-life impact of natural dust on atmospheric processes it is of vital importance to work directly with the natural samples, both to observe the real effects of desert and volcanic dusts and to evaluate the relevancy of proposed proxies.
In the context of coupling nonthermal plasmas with catalytic materials, CeO2 is used as adsorbent for toluene and combined with plasma for toluene oxidation. Two configurations are addressed for the ...regeneration of toluene saturated CeO2: (i) in plasma-catalysis (IPC); and (ii) post plasma-catalysis (PPC). As an advanced oxidation technique, the performances of toluene mineralization by the plasma-catalytic systems are evaluated and compared through the formation of CO2. First, the adsorption of 100 ppm of toluene onto CeO2 is characterized in detail. Total, reversible and irreversible adsorbed fractions are quantified. Specific attention is paid to the influence of relative humidity (RH): (i) on the adsorption of toluene on CeO2; and (ii) on the formation of ozone in IPC and PPC reactors. Then, the mineralization yield and the mineralization efficiency of adsorbed toluene are defined and investigated as a function of the specific input energy (SIE). Under these conditions, IPC and PPC reactors are compared. Interestingly, the highest mineralization yield and efficiency are achieved using the in-situ configuration operated with the lowest SIE, that is, lean conditions of ozone. Based on these results, the specific impact of RH on the IPC treatment of toluene adsorbed on CeO2 is addressed. Taking into account the impact of RH on toluene adsorption and ozone production, it is evidenced that the mineralization of toluene adsorbed on CeO2 is directly controlled by the amount of ozone produced by the discharge and decomposed on the surface of the coupling material. Results highlight the key role of ozone in the mineralization process and the possible detrimental effect of moisture.
The VOC emission processes from a solid material can be described by three key parameters: the partition coefficient (K), the initial emittable concentration (C0) and, the diffusion coefficient (D). ...These emission key parameters need to be determined experimentally for a VOC-material pair. A new method from literature allows determining simultaneously the three emission key parameters. However, this method has been evaluated in a single experiment only for formaldehyde. Therefore, the purpose of this study is to assess the efficiency and the reproducibility of the experimental method from literature performing three tests in the same experimental conditions. This work permits to determine the three key parameters of eight main VOC emitted from a particleboard and to evaluate the accuracy of the experimental method. Successfully, experiments carried out using a 128 L well-mixed chamber containing a particleboard, and connected to an online gas analyzer (Selected Ion Flow Tube-Mass Spectrometry), allow the effective characterization of the source material. Results evidence that compared to other VOCs, formaldehyde shows a specific behaviour: the response of formaldehyde between airtight and ventilated regimes is highly contrasted with those of other emitted VOCs.
Indoor air quality (IAQ) receives an increasing attention because of long-term occupancy of confined environments with high specific pollutant concentrations, especially volatile organic compounds, ...inducing a risk for human health. Standard air quality instruments are not adapted for long-term continuous real-time monitoring of these environments, and a promising alternative resides in using electronic gas sensors, which are miniature and low-cost devices capable to detect air pollutants, even at low concentrations.
The present study focuses on IAQ monitoring with electronic gas multi sensor systems, as well as with typical indoor air analyzers in a 40 m3 experimental room. The suitability of electronic gas sensors to monitor pollution events in indoor environments, characterized by transient concentrations of VOCs, has been characterized by simultaneous injections of acetaldehyde, acetone, formaldehyde, toluene and o-xylene. The impact of a green wall structure in the room has been assessed by the reduction of residual pollutant and higher decay of injected oxygenated VOCs than in the empty room. It has been shown that electronic gas sensor response show a good correlation within the analyzer measurements, both for injected VOC concentrations and their decay. Indeed, these systems provide relevant information for air treatment control system and detection of indoor air quality events, in the case of simple gas matrixes, however realistic complex matrixes are poorly monitored by electronic gas sensors selected in this study. This limitation could be overcome by increasing the number of sensitive sensors to indoor air specific composition.
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•The performance of multisensor arrays to monitor an indoor event have been assessed.•The sensor response has been successfully confronted to analytical measurements.•Due to low selectivity, the quantitative analysis of VOC mixtures is difficult.•As a case study, the effect of a green wall on indoor pollution has been estimated.
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