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.
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.
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.
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.
The heterogeneous interaction of limonene and toluene with Saharan dusts was investigated under dark conditions, pressure of 1 atm, and temperature 293 K. The mineral dust samples were collected from ...six different regions along the Sahara desert, extending from Tunisia to the western Atlantic coastal areas of Morocco, and experiments were carried out with the smallest sieved fractions, that is, inferior to 100 μm. N2 sorption measurements, granulometric analysis, and X-ray fluorescence and diffraction (XRF and XRD) measurements were conducted to determine the physicochemical properties of the particles. The chemical characterization showed that dust originating from mideastern Sahara has a significantly higher SiO2 content (∼82%) than dust collected from the western coastal regions where the SiO2 relative abundance was ∼50%. A novel experimental setup combining diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), selected-ion flow-tube mass spectrometry (SIFT–MS), and long path transmission Fourier transform infrared spectroscopy (FTIR) allowed us to follow both the adsorbed and gas phases. The kinetic adsorption/desorption measurements were performed using purified dry air as bath gas, exposing each dust surface to 10 ppm of the selective volatile organic compound (VOC). The adsorption of limonene was independent of the SiO2 content, given the experimental uncertainties, and the coverage measurements ranged between (10 and 18) × 1013 molecules cm–2. Experimental results suggest that other metal oxides that could possibly influence dust acidity may enhance the adsorption of limonene. On the contrary, in the case of toluene, the adsorption capacities of the Saharan samples increased with decreasing SiO2 content; however, the coverage measurements were significantly lower than those of limonene and ranged between (2 and 12) × 1013 molecules cm–2. Flushing the surface with purified dry air showed that VOC desorption is not a completely reversible process at room temperature. The reversibly adsorbed fraction and the rate coefficients of desorption, k des, depended inversely on the SiO2 relative abundance for both VOCs.
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 adsorption properties of mineral dust toward organic molecules are poorly characterized so far. Heterogeneous processes between trace gases and mineral particles can affect the oxidative capacity ...of the atmosphere as well as constitute additional sources or sinks for these species. The current study investigates the adsorption efficiencies of natural dust samples collected from North and West Africa, Saudi Arabia, and Arizona desert regions toward isopropyl alcohol (IPA), a common organic pollutant released in significant amounts in the atmosphere, which is used here as a probe molecule. Experiments are performed under atmospheric pressure, room temperature 296 K, over the concentration range (0.15–615) × 1013 molecules cm–3, and in the relative humidity (RH) range (0.01–85)%. The kinetic measurements are conducted inside a U-shaped flow reactor using zero air as bath gas and a chemical ionization mass spectrometer for real-time gas-phase monitoring. Kinetic and surface parameters such as initial uptake coefficients (γ0) and adsorption equilibrium constants are measured. γ0 is found to be independent of the IPA gas-phase concentration. However, concerning RH, γ is independent up to ca. 20%, but a dramatic decrease is observed above that threshold implying a competition between water molecules and IPA after the formation of a water monolayer on the dust sample. These results are simulated using an empirical expression of the form γRH = γdry – aRH b that allows the extrapolation of the uptake coefficient under any tropospheric RH conditions. Our uptake coefficient values show a linear correlation with the elemental Al/Si and Fe/Si ratios of the natural dusts studied. This was confirmed when comparing with data on inorganic species gathered from a comprehensive literature review (no such data exist for organics). To the best of our knowledge, this work is the first to demonstrate that initial uptakes are linearly correlated with the Al/Si ratio for both organic and inorganic species.
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.
•In situ DRIFT spectroscopy was employed to monitor the dust surface.•XRF, XRD and ICP-MS analyses were used for the chemical characterization of dusts.•Particles Size and the Ca/Si ratio could ...determine water adsorption onto dust.•At ambient relative humidity, natural mineral samples are always covered with water.
The adsorption of water molecules on natural mineral dusts was investigated employing in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). The natural dust samples originated from North and West Africa, Saudi Arabia and Gobi desert regions. Furthermore, the hygroscopicity of commercially available Arizona Test Dusts (ATDs) and Icelandic volcanic ash were examined. N2 sorption measurements, X-ray fluorescence and diffraction (XRF and XRD), as well as Inductively Coupled Plasma Mass Spectrometry (ICP-MS) analyses were performed to determine the physicochemical properties of the particles. The water adsorption experiments were conducted in an optical cell, at room temperature under the relative humidity (RH) range of 1.9–95%. Results were simulated using a modified three-parameter Brunauer-Emmett-Teller (BET) equation. Water monolayer (ML) was formed in the RH range of 15–25%, while additional water layers were formed at higher RH. Besides, the standard adsorption enthalpies of water onto natural mineral dust samples were determined. A thorough comparison of two commercially available ATD samples indicated that size distribution and/or porosity should play a key role in particle hygroscopicity. Regarding the natural mineral particles, Ca/Si ratios, and to a lesser extent Al/Si, Na/Si, Mg/Si ratios, were found to impact the minimum RH level required for water monolayer formation. These results suggest that the hygroscopic properties of investigated African dusts are quite similar over the whole investigated RH range. Furthermore, one of the major conclusions is that under most atmospheric relative humidity conditions, natural mineral samples are always covered with at least one layer of adsorbed water.
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