Online & Oslo, Norway
21-23 June 2021
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Session 1: Indoor chemical pollutants
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10:30am - 10:35am
Impact of indoor temperature on the possible release of adsorbed Volatile Organic Compounds from sorptive materials
1IMT Lille Douai, SAGE, Université de Lille, 59000 Lille, France; 2Saint-Gobain Research Paris, 93300 Aubervilliers, France
The removal of indoor Volatile Organic Compounds (VOCs) by sorptive processes on the surfaces of construction materials is a promising alternative to conventional air treatment systems. Implementing Activated Carbons (ACs) in construction materials is a way to improve the global uptake abilities of the products. However, uptake capacities of indoor material are mostly investigated under mild ambient temperature and humidity, while these parameters fluctuate on long-term, questioning the fate of taken up species. Depending on thermal conditions, sorptive air treatment materials may act as secondary sources of taken up VOCs.
This work questions the behavior of Activated Carbon (AC) regarding toluene uptake and release under a wide temperature range. In this work, after toluene uptake, Isothermal Desorption (ID) originally completes the classical Temperature-Programmed Desorption (TPD). TPD consists in linearly increasing the temperature until high values to induce a complete desorption under controlled heating rate. Its interest for indoor conditions is limited because of heating rate and extreme temperature range. ID relies on submitting the system to successive temperature steps. The selection of temperatures of interest along ID experiments is useful to study the behavior of ACs under realistic indoor conditions.
Experiments evidence that, from the temperature threshold of toluene desorption (Tstart) until the maximum temperature (Tpeak), both retrieved by TPD, the quantity of desorbed toluene linearly increases with the temperature set. Consequently, it can be stated that until Tstart, AC does not behave as an indoor secondary source. However, at higher temperatures, the quantity of released toluene can be predicted through linear regression by knowing the temperature of the AC surface. Finally, after Tpeak, the material is exhausted as all the taken up toluene have been desorbed. However, it should be noted that typical Tpeak values are far from any indoor conditions. Thus, a fraction of the toluene taken up is not releasable under indoor conditions.
This study points at the complementarity of both desorption methods, the classical TPD and the innovative ID, for characterizing the taken up toluene on ACs. Moreover, this result is useful to predict the quantity of adsorbed VOCs that are desorbed from sorptive air treatment materials for any given temperature. Therefore, the implementation of these processes in IAQ models allows improving their representativeness. As the study has been performed on ACs only, the conclusion given in this abstract has to be confirmed with desorption tests on the final product, i.e. the AC-doped construction material.
10:35am - 10:47am
Characterization of the surface chemistry of Activated Carbons: a tool for sorptive indoor material formulation
1IMT Lille Douai, SAGE, Université de Lille, 59000 Lille, France; 2Saint-Gobain Research Paris, 93300 Aubervilliers, France; 3Ceramic Synthesis and Functionalization Laboratory (LSFC), UMR 3080, CNRS/Saint-Gobain CREE, Saint-Gobain Research Provence, 84300 Cavaillon, France
The removal of Volatile Organic Compounds (VOCs) by sorptive processes involving indoor surfaces is an alternative to conventional air treatment systems. Implementing Activated Carbons (ACs) in construction materials is a way to improve the uptake abilities of these products. However, correlations between the physico-chemical properties of selected ACs and their retention capacities towards VOCs remain poorly understood, especially on realistic time scales and conditions. Specific surface area (Sspe) and surface chemistry are recognized as key parameters. But there is large diversity of indoor VOCs, which are not identically affected by these parameters.
This work aims at evaluating the impact of the surface chemistry of various ACs on VOC uptake at ambient temperature. Selected ACs have equivalent Sspe, ranging from 900 to 1200 m2.g-1. They differ in their nitrogen (N) and/or oxygen (O) content. The level of heteroatoms is controlled along their syntheses. Toluene and formaldehyde are selected as model pollutants due to their ubiquity in indoor environment and their contrasted natures. VOC uptakes on ACs are characterized by: partitioning coefficient K (μg.m-3), total adsorbed quantity qads and uptake reversibility. The surfaces of ACs are characterized using X-ray Photoelectron Spectroscopy XPS and X-ray scattering.
Regarding toluene, qads is maximum for AC without heterogeneous atoms. On the opposite, qads of HCHO is by two orders of magnitudes lower. This behavior is discussed in terms of polar interactions. The presence of N or O atoms negatively impacts the quantity of toluene taken up. On the contrary, it positively influences the irreversible nature of HCHO uptake, attesting of stronger interactions of HCHO with such modified ACs. To interpret uptake results further, characterization of the ACs are performed. XPS is used to identify the nature of the chemical groups involving the N and O atoms on the surface of ACs. X-Ray Spectroscopy (silver-based source) is considered to determine the distribution of the heteroatoms on the surface of ACs, whether homogeneously organized or clustered.
This work experimentally points at the role of the surface chemistry of ACs for indoor VOCs uptake under realistic experimental conditions. Moreover, the use of multiply surface characterization techniques is promising to better comprehend the AC surface, for identifying the most suitable ACs for VOC removal. As the study has been performed on ACs only, the evidenced contrasted behavior has to be confirmed with tests on final products, i.e. the AC-enriched construction material.
10:47am - 10:52am
Diffusions of essential oils in a 40m³ experimental room: from emission rates to impact on indoor air quality
1IMT Lille Douai, Université de Lille, SAGE, 59000 Lille, France; 2Centre Scientifique et Technique du Bâtiment (CSTB), F-38000 Grenoble, France
Essential oils have attracted increasing interest due to their performances as inhibitors of the metabolic functions of microorganisms. They are widely promoted as easy-to-use compounds to improve indoor air quality through passive remediation practices associated with their purifying actions. However, the potential toxicity of essential oils released in indoor air has not been clearly established.
This study aims to assess the emissions of terpene molecules contained in essential oils in confined environments by employing two diffusion mechanisms under real conditions in a real-scale experimental room : one ceramic heat diffuser, and one capillarity diffuser. This study also evaluates the impact of chamber volume on emission dynamics of essential oil constituents.
Evidence is found of contrasted concentration levels and kinetics depending on the diffusion mechanism used. Results show that the impact of indoor essential oil diffusion varies from 6 hours to 51 days, depending on the device used. Concentration levels can exceed recommended exposure levels by more than one order of magnitude. Additionally, the relative contributions of individual terpenes in the gas phase vary throughout the diffusion process.
Finally, several limitations are found regarding the evaluation of TerVOC emissions using test chambers with small volumes, typically in the 1 m3 range. Indeed, the concentration of TerVOCs and their emission kinetics are noticeably dependent on the chamber volume, which evidences the interest of determining emission rates using real scale and well-controled experimental chambers to provide applicable experimental data for accurate exposure assessment.
10:52am - 11:04am
VOCs emissions from the human during sleep under different ozone and air change rate levels
1School of Chemistry and Biological Engineering, University of Science and Technology Beijing, China; 2International Centre for Indoor Environment and Energy, Technical University of Denmark, Denmark
INTRODUCTION: Indoor pollutants emitted from occupants, which is bioeffluents, have attracted great attention of researchers. As a major part of bioeffluents, the components and emission rates of VOCs have been investigated. While most of the studies were conducted when occupants were awake. There is very limited knowledge of VOCs emission rates from sleeping people. Therefore, the present study was performed in a climatic chamber to estimate VOCs emission rates from sleeping people to fill in this gap.
METHOD: Eight healthy college-age subjects were recruited to sleep at three different conditions in a specially constructed capsule located in the chamber to create a small confined space. The three conditions consisted of two ozone levels (with a concentration of 0 and 25 ppm) and two air change rates resulting in CO2 concentrations of about 800 ppm and 1700 ppm respectively. The temperature was 24 °C. Activated carbon was installed at the inlet of the air in the ventilation system to remove ozone in the background. An ozone generator was applied to doze a specific amount of ozone to the capsule. Each subject slept in a balanced order. VOCs in the capsule were sampled before and during sleep at a fixed time with Tenax tubes. The samples were then determined by thermal desorption - gas chromatography-mass spectrometry. Two typical pollutants, acetone and isoprene, were selected to estimate VOCs emission rates using a mass-balance equation.
RESULTS: The emission rates of isoprene and acetone emitted from sleeping people were around 0.08 mg·h-1 and 0.06 - 0.2 mg·h-1 respectively, which were much lower than that emitted from awake people (the emission rates for isoprene and acetone were about 0.16 mg·h-1and 1.0 mg·h-1 respectively). Meanwhile, the results indicated that dosing ozone into the capsule could increase the concentration and emission rate of acetone, but had little influence on that of isoprene. While increasing the air change rate could decrease the concentrations of both isoprene and acetone significantly. It also increased the emission rate of acetone but decreases the emission rate of isoprene slightly. Further research needs to be performed to explore the mechanism of the influence of ozone and air change rate on VOCs emissions during sleep.
11:04am - 11:16am
Modeling physico-chemical processes impacting particles formation and fate indoors
1Université de Strasbourg, CNRS, Laboratoire Image Ville et Environnement (LIVE), UMR7362, Strasbourg, France; 2French Environment and Energy Management Agency (ADEME), France; 3Octopus Lab, La Madeleine, France; 4Laboratoire des Sciences du Climat et de l’Environnement, UMR 8212 CEA-CNRS-UVSQ, Gif-sur-Yvette, France
People spend on average 80% of their time indoors while several monitoring campaigns showed that high levels of organics and particulate matter (PM) could be reached (Blanchard et al., 2014; Morawska et al., 2017). Conventional indoor air quality (IAQ) diagnostics are based on measurements, and thus expensive and time-limited. To overcome this issue, several models simulating aerosols concentration indoors have emerged. However, most of them disregard aerosol formation via condensation of Semi-Volatile Organics (SVOCs), which turns out to be one of the main source. . Indeed, this requires a good knowledge of SVOCs concentrations in the gaseous phase.
To overcome this need, this study aims at developing and validating a numerical model for simulating aerosols indoors based on the INCA-Indoor model which has been developed to simulate concentrations of various volatile and semi-volatile organic compounds and oxidants in multi-rooms (Mendez et al., 2015). INCA-Indoor model showed good agreement in reproducing the gas phase (Mendez et al., 2015, 2016, 2017) and is currently used to carry out IAQ studies in support of building design projects (www.octopuslab.fr).
The aerosol module simulates the different physico-chemical processes impacting aerosols concentration both in number and mass: coagulation, nucleation, condensation with the use of the H2O model (Couvidat et al., 2012), indoor-outdoor exchange and deposition.
The robustness of the model is evaluated thanks to a comparison between simulation results and experiments in simulation chambers. Two types of aerosols have been selected to cover several processes: 1- coagulation from Diesel soot in the AIDA chamber (KIT) and 2- Secondary Organic Aerosol (SOA) formation after an ozonolysis reaction in the EUPHORE chamber (CEAM).
Results show good agreement between simulation and measurements: the RMSE between the observed value and the simulated value is less important than the uncertainty on the measurement. The model simulations are therefore in the uncertainty interval on the observation.
To conclude, this model is promising to better account for aerosols formation and fate when designing healthy buildings.
11:21am - 11:33am
Effect of ageing conditions on decorative and renovation products containing biocides: Assessment of its impact on indoor air quality
1IMT Atlantique, France; 2IMT Lille Douai, France
Building and finishing materials are among the main sources of indoor air pollution. Depending on the environmental conditions, these materials can be exposed to physico-chemical ageing and prone to microbial growth. The ageing process may affect indoor air quality (IAQ) throughout the emission of Volatile and Semi Volatile Organic compounds (VOCs and SVOCs). In order to prevent the biological growth, nowadays, some manufacturers add biocides to building and decorative materials.
The aim of this study is to develop a methodology in order to evaluate the impact of the ageing process on the effectiveness of biocides and on the emissions of VOCs and SVOCs. To do so, a renovation plaster (decorative material) was added to a polyester-cellulose (wall covering) before being subjected to accelerated ageing. The latter process consists of adding a detergent and exposing the material to a visible light spectrum, high relative humidity, and moderate temperature. The aged and non-aged materials were inoculated by fungal spores using a dry aerosolization system prior to incubation. Developed fungi were then quantified using the cultured cell method.
The emission rates of VOCs and SVOCs from the aged, non-aged, inoculated, or non-inoculated materials were determined using the Field and Laboratory Emission Cell (FLEC). Gas samples were collected for each material after three days of emission. The identification and quantification of the emitted compounds were carried out using gas (TD-GC-MS/FID) and liquid (HPLC) chromatography.
The obtained results by the cultured cell method showed a proliferation of inoculated mold on the surface of the non-aged polyester-cellulose, whose concentration of developed spores was 10 times higher than the concentration of deposited spores. Whereas, no visible growth was detected on the polyester-cellulose combined with the renovation plaster, before and after ageing.
Regarding VOCs/SVOCs emissions, 64 compounds were emitted from the non-aged materials, out of which 5 are SVOCs. The emission rates of 29 compounds decreased with ageing, in particular biocides, whereas 17 other compounds have “newly” emerged. Similar results were obtained after the inoculation and incubation processes which led to a decrease in the emission rates of 37 compounds and the appearance of 7 “new” VOCs. However, the behavior of compounds was more variable when comparing emissions from the aged materials to those from the inoculated and incubated materials.
This study can be used to evaluate the lifespan of the applied biocides and to evaluate of the potential impact of ageing on IAQ.
11:33am - 11:38am
Indoor Environment and Energy Consumption of an Elementary School in a Subtropical Region
1University of the Ryukyus; 2Sogo Keikaku Sekkei Co., Ltd.; 3Satoh Energy Research Co., Ltd; 4Waseda University
Indoor thermal and air quality environments were measured in a subtropical region to clarify the performance and utilization of air conditioning system. The target school is existing in Okinawa, Japan, of which the latitude is about 26.2N. Annual maximum and minimum temperature is about 35 C 15 C and the RH is always over 75%. All the school buildings are equipped with air conditioning systems (ACs) because of not only hot and humid circumstances but also noise of airplanes. However, ACs without ventilation often make higher concentration of CO2 in the indoor air. It is necessary to operate and manage ACs and natural ventilation correctly to achieve and keep better thermal comfort and air quality and to save energy. The measurement results show the following environmental conditions: (1) The ACs were worked when the daily average air temperature was over 22deg. C. (2) The ACs in the class rooms were controlled by the teachers individually, and sometimes the room air temperatures were overcooled. (3) Direct solar radiation penetrated the class rooms in the early morning, which increased the heat load of ACs. (4) Vertical distribution of air temperature in the class rooms was clear, the higher point the higher temperature under air conditioning. (5) The concentration of CO2 in the class rooms were kept under 1000ppm by heat exchange ventilation systems.
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