WOOD BORNE EMISSIONS IN A REAL ROOM ENVIRONMENT- A MODELLING APPROACH

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1 WOOD BORNE EMISSIONS IN A REAL ROOM ENVIRONMENT- A MODELLING APPROACH Martin Weigl 1, Daniel Stratev 2, Christina Fürhapper 3, Elisabeth Habla 4, Michael Nohava 5, Sabrina Niedermayer 6 ABSTRACT: This work presents a comprehensive overview on studies performed by Holzforschung Austria related to volatile and very volatile organic compound (VOC and VVOC) emissions from wood and wood products carried out in a full scale level. Scaling is crucial and due to material combinations additional sinks appear and sorption and diffusion of the monitored substances occurs. Hence, full scale analyses partly reflect differences compared to standard chamber tests. Long term emission results from 30 m³ model rooms, office container buildings and residential houses are presented. These long term emission profiles were mathematically modelled. The models show, that high safety margins get accepted for wooden products as long term emissions don t get considered in standard emission tests for building products. KEYWORDS: VOC, TVOC, formaldehyde, indoor air quality, full scale, model room, long term emission 1 INTRODUCTION 123 The influence of building materials on the indoor air quality is a widely discussed topic. Especially bio-based products such as engineered wood products are often seen as highly emitting. Depending on national building regulations or site specific tender, application of such products might be limited or even prohibited. Special focus is given with respect to the concentration of formaldehyde, organic substances showing toxic, carcinogenic, mutagenic or reproduction toxic properties, as well as on volatile organic compounds in general, independent from their toxicological potential. For example, the Austrian Academy of Science in cooperation with the Austrian life ministry BMLFUW published a guideline for the assessment of the indoor air 1 Martin Weigl, Holzforschung Austria, division for, Franz-Grill-Str. 7, 1030 Vienna, Austria, m.weigl@holzforschung.at 2 Daniel Stratev, Holzforschung Austria, division for 3 Christina Fürhapper, Holzforschung Austria, division for 4 Elisabeth Habla, Holzforschung Austria, division for 5 Michael Nohava, Holzforschung Austria, division for 6 Sabrina Niedermayer, Holzforschung Austria, division for quality [1]. Currently an Austrian Standard for indoor air quality requirements is created [2]. However, such regulations can only be applied for the assessment of buildings after a certain aging phase. Indoor air quality measurements within the phase of construction or in the early phase of settlement usually underlie a very dynamic alteration. Especially for bio-based building materials such as wood and engineered wood products, it is currently not possible to guarantee such indoor air quality parameter due to several reasons. For example, there is a discrepancy between building product selection based on standardised chamber testing (e.g. based on [3] or [4]) results and the real life behaviour of wood borne emissions. Calls within the building industry often include emission requirements based on such product tests, but they do not reflect the indoor air environmental condition after construction. Due to deviations from the standard conditions, scaling phenomena and interactions with other materials (adsorption, desorption, diffusion), emission kinetics and real life indoor air quality cannot be precisely predicted only based on results from standardized product tests. Discrepancies between predicted concentration values and results from in situ measurements can be very wide, such is the case with the sauna building guideline developed by [5], including a threshold for formaldehyde within the sauna indoor air. Product testing for this application is performed based on [6], but under elevated temperature, leading to frequent product fail.

2 This work gives an overview on the results from three independent research projects performed at Holzforschung Austria within this topic. Special focus is the potential of mathematical modelling of the long term emission development that can be used for future engineering applications. 5. OSB covered by vapour barrier (sd 100m) and plaster board Examples of the internal fitting of the model rooms are shown in Figure 2. 2 MATERIAL AND METHODS Three independent case studies focused on long term emission development were conducted. Sampling of indoor air and measurement of VOC (volatile organic compounds) and lower carbonyl substances (e.g. formaldehyde) was performed according to [7] and [8]. Sorption media for indoor air sampling were TENAX for VOC and DNPH for carbonyls. Evaluation of indoor air concentrations was based on substance specific calibration of the TD-GC-MS (thermodesorption gas chromatograph with mass spectrometer detector; Markes international UNITY plus Agilent Technologies 6890N and 5973) and HPLC-DAD (high performance liquid chromatography with diode array detector; Thermo Scientific DIONEX Ultimate 3000) measurement devices. In total, calibration covered around 70 to 80 individual substances. Evaluation of the indoor air concentration of each chemical substance found was in accordance with requirements of the above mentioned standards respectively [9] and [10]. In order to simplify data presentation TVOC values (i.e. the total sum of VOCs) instead of single substance concentrations will be shown. 2.1 CASE STUDY 1: MODEL ROOM DESIGN AND LONG TERM MEASUREMENTS Within the five year project HFA-TiMBER [11] field and laboratory emission cell (FLEC, [12]) and testchamber [4] measurements as well as sorption- and diffusion experiments [13], [14] were used as assessment tools for the selection of construction materials for building up of two model rooms according to [15], [16]. These two model rooms had a free air volume of 30 m³ (3 x 4 x 2.5 m). Model rooms were created as timber frame construction and had one door (1.6 m²) and one window (2 m²) (Figure 1) constructed from emission inert materials. Independent air ventilation and conditioning system allowed climate conditions such as used within standard test chambers [4]. The external walls construction included a diffusion dense Aluminium foil, in order to exclude VOC and air exchange with the surrounding. The internal wall and ceiling panels were changed depending on the test trial needs. The total indoor air exposed surface was 55.4 m² (excluding the door and window), leading to a loading of 1.8 m²/m³. Within the trials the following five industrial building products (and their combinations) were used as internal walls and ceilings: 1. OSB 2. Plaster board 3. OSB covered by plaster board 4. OSB covered by vapour barrier (sd 10m) and plaster board Figure 1: Timber frame construction of a single model room Figure 2: Indoor exposed surfaces within the model rooms (left: OSB, right: plaster board). All board edges were sealed (OSB: tape, plaster board: gypsum) Long term development of VOC concentrations (emissions) was studied aiming on the determination of the steady state, which strongly depended on the applied construction materials and the construction principal. Hence the trials were stopped after 27 weeks (OSB), 7 weeks (plaster board), 20 weeks (OSB/plaster board), 32 weeks (OSB/vapour barrier 10m/plaster board), and 16 weeks (OSB/vapour barrier 100m/plaster board) respectively. 2.2 CASE STUDY 2: LONG TERM INDOOR AIR ENVIRONMENT DEVELOPMENT IN WOODEN OFFICE CONTAINERS Within the research project Baubiologische Containerentwicklung - BigConair, real environment experiments were performed at a bigger scale compared to the above mentioned model rooms, within temporary office containers (Figure 3). The following containers were assessed: 1. Crosslaminated timber (X-Lam; Figure 3 in the front) made of spruce wood 2. Clay-covered timber frame (Figure 3 in the back) made of spruce wood 3. Standard 20 double container made of steel (reference container not shown) 4. Renovated standard 20 double container made of steel with clay walls and ceiling (not shown)

3 Figure 3: Office container at University of Innsbruck (X-Lam container with larch wood planks (front) and timber frame container with shingles (back)) Thermal insulation of the two wooden office containers was made of hemp and sheep wool. Both were prefabricated and delivered as half containers and assembled ready for use within two days, directly at the site. The reference container had already been in use for ten years, and at first no alterations were made in his construction. In order to improve comfort and indoor air quality, the reference container was renovated (by covering it with clay) in a later phase, which is indicated in the list above with number 4. Long term monitoring of VOC- and formaldehydeconcentrations in the indoor air were performed until a steady state was reached and most commonly further conducted thereafter: X-Lam (180 days for steady state, total 620 days), timber frame with clay (no steady state, total 610 days), reference (28 days for steady state, total 610 days), and renovated reference with clay (40 days for steady state, total 450 days) respectively. Additionally, standard office furniture consisting of particle board based two L-shaped tables, two book shelves, and one simple table, as well as three ordinary chairs were used within these containers. The additional emission of the office furniture was assessed based on comparison of measurements within the same object, once with and once without furniture. For this purpose, the whole furniture was removed, the container actively ventilated and sealed for 14 h before sampling. 2.3 CASE STUDY 3: RESIDEAL HOUSING IN AN WOODEN ENVIRONMENT Wood2New is a project which is currently running and presents an upscaling of BigConair. Here the measurements are made under real-life conditions. Development of indoor air quality within the first half year after move in is accessed based on a monitoring of VOCs, VVOCs, airborne microorganisms, and particulate matter. These measurements get aligned with health-related parameters such as pulmonary function, eyelid blink rate, blood pressure, pulse, and an overall health status assessment by means of medical surveys. More details on the methods applied were published by [17]. The assessment covers 13 individual buildings, whereas one serves as a reference as it was no wooden construction. Sampling of the indoor air was always done within the bedroom, as this is usually the room humans spend the most time at once and ventilation of the room is usually not altered during sleep. The first measurement was usually performed roughly within the building phase, but at least after installation of windows and doors, most commonly after all painting work and installation of the flooring. The second sampling was done after move in, as additional emissions from furniture, fast moving consumer goods, and human activities were expected. Thereafter, sampling was done monthly. Approximately 100 samples were taken (sampling device for VOC: Figure 4). Since the process of measurement is currently ongoing only preliminary results are presented here. Figure 4: Sampling device for the collection of VOCs on TENAX -Tubes applying FLEC-pumps (first sampling before move in: no furniture inside; object not jet in use) 3 RESULTS AND DISCUSSIONS 3.1 CASE STUDY 1: MODEL ROOM DESIGN AND LONG TERM MEASUREMENTS A general decrease of VOC concentrations could be found throughout weeks and months after the completion of the model rooms. Preliminary results were actually published by [18] and [19]. Figure 5 demonstrates the long term development of the TVOC concentration for the five different model room fittings. Figure 5: Long-term TVOC [µg/m³] development of different wall constructions demonstrated in model rooms (day 28 and rating according to [1] are indicated): OSB (yellow with diamonds), plaster board (red with crosses), OSB/plasterboard (blue with boxes), OSB/sd10/plaster board (purple with triangle), and OSB/sd100/plaster board (green with triangle).

4 The day 28 is highlighted, as this is the time for the evaluation of the VOC emissions from building products, e.g. conducted according to [4]. Additionally, the rating system for the indoor air quality according to [1] is highlighted, which will serve as a reference according to the TVOC classes low, average, slightly elevated, distinctly elevated and strongly elevated (latter was never reached within the trial). The pattern of the declining curve of the TVOC concentrations over time was primarily associated with the type of building material and the construction type. The coating of OSB with vapour barrier and/or plasterboard led to a decrease of the (initial) TVOC concentration and influenced the TVOC emission kinetics. The highest initial TVOC concentration was found for the non-covered OSB model room within the first days, showing a steep decline thereafter. On day 28 the TVOC value reached approximately 500 µg/m³. This actually equals the transition between slightly elevated and average indoor air concentration. However, a further decline throughout the whole sampling period was observed, and a further reduction at the end of the trial could be gained by increased air exchange rate. The best evaluation rating could be reached even with noncovered OSB if the model room is ventilated long enough. Very low TVOC concentrations and just a slight reduction could be observed for the plaster board model room. On day 28, this model room actually reached the criterion for a low TVOC concentration. Covering OSB with plaster board led to a reduced maximum TVOC compared with the simple OSB model room, and at least comparable results for the day 28 and the following months. Additional installation of the sd 10 m vapour barrier between OSB and plaster board altered the VOC evaporation kinetics and led to a reduction in the TVOC decrease over time. Thus this building products combination was characterised with the highest TVOC concentration on day 28 and the following 20 weeks all rated as slightly elevated (with one exception). Finally for the measurement in week 32 after installation, the TVOC concentration was rated as average. The installation of sd 100 m vapour barrier led to a stronger reduction of the TVOC value within the first 28 days which stayed low throughout the following weeks, and also led to a good rating of the indoor air quality. However considering the sd 10 m results it was of interest how long the sd 100 m TVOC value would have stayed stable around the value of day 112. Unfortunately the experiment design did not allowed further measurements. These results demonstrate 1) that evaluation of building products emissions on day 28 do not reflect the actual long term situation within a building at least if the products of interest (such as wood based products) tend to a strong decline in their VOC emissions, and 2) emission engineering is possible for example by the means of selection of proper materials and proper material combinations. Thus even high emitting materials could achieve good evaluation. 3.2 CASE STUDY 2: LONG TERM INDOOR AIR ENVIRONMENT DEVELOPMENT IN WOODEN OFFICE CONTAINERS Figure 6 summarises all results for the TVOC within this trial. Besides the curves for the four different containers (straight lines), two additional curves are shown (dashed lines). The latter demonstrate the additional effect on the TVOC within the reference and the X-Lam container originating from the office furniture. Such as for Figure 5, the day 28 and the grading criteria are indicated. The lowest TVOC concentrations were found for the reference container. Throughout the whole experiment, this container showed a low TVOC. Renovation of this container with clay surfaces led to a short increase of TVOC until day 28 leading to a value graded as average, followed by a steep drop directly after and comparable results towards the reference. The X-Lam container showed a typical TVOC decline right from the beginning. On day 28, the TVOC concentration is actually graded as average, after three months as low and latest after six months as comparable to the reference container. The highest TVOC concentrations were found for the timber frame container throughout the whole experiment. On day 28, values were rated as distinctly elevated. After 30 weeks, values were rated as slightly elevated and after approximately one year, values were average. A steady state was not found in this case within the whole trial. A distinct increase was observed after the temperature increase from 20 to 33 C, which immediately decreased after temperature was set back to 20 C. Figure 6: Long-term TVOC [µg/m³] development in the four different office containers (day 28 and rating according to [1] are indicated): reference (blue with diamonds), renovated reference (red with dots), X-Lam (brown with triangles), and Timber frame (green with boxes). Furthermore, the additional effect of the furniture is indicated in two cases, as well as one singular temperature effect. In case of the X-Lam and the reference container, the additional effect on the TVOC coming from the furniture can be seen in Figure 6. In both cases, the furniture gave an immediate measurable additional effect. The absolute addition in terms of TVOC was comparable for both containers. At the beginning of the furniture experiment, the TVOC slightly exceeded the current indoor air quality grade of the corresponding container without furniture: reference increased from low to average, and X-Lam from average to slightly increased. However,

5 within reasonable time, this additional furniture effect decreased, and the containers were graded the same way, independent from the existence of furniture inside. 3.3 CASE STUDY 3: RESIDEAL HOUSING IN AN WOODEN ENVIRONMENT Case study 3 is still ongoing. Hence, just preliminary results for the long term development of the formaldehyde concentration in residential sleeping rooms are demonstrated here. Figure 7 gives a comparison of the formaldehyde concentrations in two sleeping rooms of independent buildings. Both were built as a timber construction. Three different safety limits are indicated: 1) 24 h safety limit of 60 µg/m³, 2) ½ h safety limit of 100 µg/m³, and 3) a toxicologically derived limit of 120 µg/m³. The first two get applied in Austria [1], the second one was set by [20], and the third one was derived based on a toxicological literature review by [21]. Figure 7: Preliminary results for formaldehyde concentration [µg/m³] development within two independent residential sleeping rooms (solid wood construction). Additionally three different safety limits in the range between 120 and 60 µg/m³ are indicated. The two observed objects show big differences in the pattern of their formaldehyde concentration functions over time. In one case, a high formaldehyde concentration was found during the phase before move in (e.g. 3.5 times higher than the WHO safety limit). However, at the time of move in, the concentration was actually underneath the strictest of the above mentioned safety limits and stayed underneath throughout the whole monitoring period. It is assumed, that the high formaldehyde concentrations at the beginning is due to evaporation from freshly installed building products, such as wood based panels bound via formaldehyde based resins. Most likely these formaldehyde sources were fabricated shortly before installation without intensive ventilation and brought in within a short time. However, due to separation and installation of these building products, evaporation of free formaldehyde could take place within short time, explaining the steep decrease. This effect was probably further promoted due to human activities such as automated or on purpose ventilation, or e.g. installation of further building products or explosion of any material that absorbs formaldehyde. In the other case, a slight but constant increase of the formaldehyde concentration could be observed, starting at a comparable low value. Within the observation time, all measurements stayed below the WHO safety limit. Assuming the above discussed scenario for formaldehyde decrease in a freshly built wooden house is typical, especially if formaldehyde based resins were used, there seems to be a significantly different building situation in the second case. This might be due to longer ventilation of the applied building products as well as due to application of formaldehyde free or lower formaldehyde emitting building products. Even native wood contains a relevant portion of formaldehyde [22]. However, the starting value can be seen as typical, whereas the further increase of formaldehyde concentration in the indoor air seems to be not related to building products, as they typically show a decrease. An additional effect such as in case study 2 coming from the furniture is also unlikely. In the before mentioned case study 2, the additional effect of furniture on TVOC was seen an immediate appearing and quickly disappearing peak, and a similar effect for formaldehyde can be assumed. Such an effect can t be seen in Figure 7. The alteration of the formaldehyde concentration within the objects of case study 2 was reported by [23]. Starting values between 15 and 35 µg/m³ were found within the office containers. Especially the two wooden containers showed a constant decrease throughout the following months and values in the range of 10 µg/m³ after one year. In total, the values reported there show a similar trend such as for the first discussed curve (orange) in Figure 7. If the second curve (blue) in Figure 7 can t be explained by typical building product behaviour or a furniture effect, it is most likely an anthropogenic effect, e.g. caused by activities such as smoking indoor. In total, these values actually demonstrate the complexity of emissions into the indoor air coming from a combination of building products (with other interior related products). 3.4 DESCRIBTION MODELL FOR LONG-TERM EMISSION DEVELOPMENT In the above discussed case studies, significant decrease of wood product related emissions after day 28 could be seen. It is also known that wood based products most commonly show a further VOC decrease after day 28 if tested under standard conditions in emission chambers. However, if the actual VOC concentration on day 28 within such a test is taken as the characteristic long term product property, an additional safety margin is accepted [24]. In order to evaluate such safety margins, natural variability within the emission profiles must be filtered. The safety margin is than calculated by dividing the accepted value (usually the value on day 28) by the steady state value (a definition for steady state should also be introduced). This procedure was applied for the VOC values (individual substances and TVOC) of the data from case study 1 and 2, in order to evaluate such safety margins within a built environment [24]. In this case, the day 28 after installation is different from the day 28 after construction. However, there is an increasing tendency to access the indoor air quality within reasonable time after construction, e.g. in order to proof if site specific

6 tender requirements are fulfilled. Hence, day 28 was taken as an example for such an indoor air assessment. A simple model was applied for the description of the VOC decline: the iterative nonlinear model applied for the calculation of the formaldehyde steady state concentration as described in [3]. The whole process is described more in detail in [24]. Figure 8 (TVOC) and Figure 9 (α-pinene) show the model fit based on two different data sets. Once, the model was calculated based on three measurement points, and the second model was calculated based on seven measurement points. In both cases, no relevant difference between the two models could be observed. In general, the applied models showed a good overall fit and just slightly overestimated the indoor air concentration around day 180. was measured. However, on a single substance base, such effects are typical. Due to different partial pressure and boiling point of the single VOCs, each substance shows a different emission pattern. The TVOC is the sum of all these substances and hence better follows this theoretical decline function than some individual once. Especially for secondary emissions, gained by autoxidation (e.g. pentanal or hexanal), worse function fit was expected. However, even for these, an adequate model fit could be gained (without demonstration here). Hence, it is assumed that the model described in [3] can be applied in general for the description of long term emissions of wood born organic compounds. The calculated safety margins for TVOC are given in Table 1, for α-pinene in Table 2 and for hexanal in Table 3. Table 1: Calculated safety margins for TVOC based on case study 1 and 2 (steady state assumed after one year) Object Safety margin OSB model room 3.4 OSB/GKF model room 2.1 X-Lam container 11.0 Timber frame container 3.7 Table 2: Calculated safety margins for α-pinene based on case study 1 and 2 (steady state assumed after one year) Figure 8: Model fit for the TVOC development within the CLTcontainer of case study 2. The 28 day value and the final value are highlighted. Object Safety margin OSB model room 3.0 OSB/GKF model room 2.2 X-Lam container 16.7 Timber frame container 21.1 Table 3: Calculated safety margins for hexanal based on case study 1 (steady state assumed after one year) Object Safety margin OSB model room 5.2 OSB/GKF model room 8.1 Figure 9: Model fit for the α-pinene development within the CLT-container of case study 2. The 28 day value and the final value are highlighted. For α-pinene, the model fit is not good for the first two measurement weeks, as an increase instead of a decrease These calculated safety margins vary between 2.1 and This means, that the real long term concentration of a single VOC or the TVOC might be between approximately 1/2 and 1/20 of the value measured on day 28. This should be considered in case of indoor air quality evaluation, especially within the early stages after construction. In buildings with automatic ventilation it would be even possible to program the air exchange rate (in accordance with the used materials) in order to (partially) compensate for the elevated initial phase TVOC emissions. After the steady state time point has been reached the ventilation could be switched to its normal program.

7 4 CONCLUSIONS Long term measurements under full scale conditions demonstrate a significant decline of emissions. VOC and formaldehyde emissions and from building products usually do not lead to concentrations that exceed the NOAL (No Observed Adverse Effect Level) concentrations, and therefore cannot be rated as harmful. Elevated emission rates at the beginning or within the construction phase usually decline towards a moderate level within reasonable time. Any kind of human activity as well as air exchange rate and additional sources of emissions most commonly have a higher impact on indoor air quality than the construction material. Models might be applied in order to describe the long term emissions development. The model described in [3] seems suitable for this approach, but needs further validation. Especially for case study 3, this approach will be applied in future. The calculated safety margins should also be considered especially for new regulations (e.g. [2]), but even for product development or product re-design. Future research will be required aiming on the creation of an objective base for the engineering of product emissions as well as for the long term development of the indoor air composition under real living conditions, based on a representative base. ACKNOWLEDGEMENT We kindly acknowledge funding within different programs for the projects HFA-TiMBER and BigConAir received from the Austrian Research Promotion Agency (FFG) as well as from WoodWisdomNet+ for the project Wood2New. Furthermore the contribution of our partners within the projects, and practical help our colleagues Peter Schober, Sylvia Pollares, Stefan Nagl, as well as from our external partners Technisches Büro für Chemie - Dr. Karl Dobianer, Wilfried Beikircher, Phillipp Zingerle, and Michael Flach from University of Innsbruck is kindly acknowledged. 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