Science of the Total Environment 874 (2023) 162319 Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv Assessment of greenhouse emissions of the green bean through the static enclosure technique Gaia Stringari a, Joan Villanueva a, Antoni Rosell-Melé a,b,1, Nuria Moraleda-Cibrián a, Francesco Orsini c, ⁎ Gara Villalba a,d, Xavier Gabarrell a,d, a Institut de Ciència i Tecnologia Ambientals ICTA-UAB MdM Unit (CEX2019-0940-M), Universitat Autònoma de Barcelona (UAB), Bellaterra, Spain b Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain c Department of Agricultural and Food Sciences, University of Bologna Alma Mater Studiorum, Bologna, Italy d Department of Chemical, Biological and Environmental Engineering, Universitat Autònoma de Barcelona (UAB), Bellaterra, Spain H I G H L I G H T S G R A P H I C A L A B S T R A C T • Unknown levels of indoor BVOC emis- sions are investigated in a building inte- grated rooftop greenhouse (i-RTG). • Dynamic sampling in static enclosure is proposed for fast BVOC emissions deter- mination in indoor systems. • Higher BVOC emissions are expected along full vegetative development. • Enclosing conditions may affect true emis- sions estimation. • Indicative BVOC levels provided are below the lowest concentrations of inter- est reported in official tables. A R T I C L E I N F O A B S T R A C T Editor: Jacopo Bacenetti Urban green installations are extensively promoted to increase sustainable and accessible food production and simul- taneously improve the environmental performance and liveability of city buildings. In addition to the multiple benefits Keywords: of plant retrofitting, these installations may lead to a consistent increase in biogenic volatile organic compounds Soilless (BVOCs) in the urban environment, especially indoors. Accordingly, health concerns could limit the implementation Hydroponics of building-integrated agriculture. In a building-integrated rooftop greenhouse (i-RTG), throughout the whole hydro- Phaseolous vulgaris BVOCs ponic cycle, green bean emissions were dynamically collected in a static enclosure. Four representative BVOCs, α- Building-integrated agriculture (BIA) pinene (monoterpene), β-caryophyllene (sesquiterpene), linalool (oxygenated monoterpene) and cis-3-hexenol (LOX Air quality derivate), were investigated in the samples collected from two equivalent sections of a static enclosure, one empty and one occupied by the i-RTG plants, to estimate the volatile emission factor (EF). Throughout the season, extremely variable BVOC levels between 0.04 and 5.36 ppb were found with occasional but not significant (P > 0.05) variations between the two sections. The highest emission rates were observed during plant vegetative development, with EFs equivalent to 78.97, 75.85 and 51.34 ng g−1 h−1 for cis-3-hexenol, α-pinene, and linalool, respectively; at plant ma- turity, all volatiles were either close to the LLOQ (lowest limit of quantitation) or not detected. Consistent with previ- ous studies significant relationships (r ≥ 0.92; P < 0.05) were individuated within volatiles and temperature and relative humidity of the sections. However, correlations were all negative and were mainly attributed to the relevant ⁎ Corresponding author at: Department of Chemical, Biological and Environmental Engineering, Universitat Autònoma de Barcelona (UAB), Campus UAB, 08193 Bellaterra, Barcelona, Spain. E-mail address: xavier.gabarrell@uab.cat (X. Gabarrell). 1 Deceased on December 2021. http://dx.doi.org/10.1016/j.scitotenv.2023.162319 Received 11 November 2022; Received in revised form 14 February 2023; Accepted 14 February 2023 Available online 18 February 2023 0048-9697/© 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC license (http://creativecommons.org/licenses/by-nc/4.0/). G. Stringari et al. Science of the Total Environment 874 (2023) 162319 effect of the enclosure on the final sampling conditions. Overall, levels found were at least 15 folds lower than the given Risk and LCI values of the EU-LCI protocol for indoor environments, suggesting low BVOC exposure in the i-RTG. Statistical outcomes demonstrated the applicability of the static enclosure technique for fast BVOC emissions survey inside green retrofitted spaces. However, providing high sampling performance over entire BVOCs collection is recom- mended to reduce sampling error and incorrect estimation of the emissions. 1. Introduction et al., 2002; Yang et al., 2009; Maffei et al., 2011; European Union, 2013). Generating data about their potential environmental fluxes can Despite the current climatic emergency and COVID-19 pandemic, the therefore be of great interest. global population increase is expected to reach 8 billion by the end of In view of prospecting scenarios and current research gaps, we carried 2022 and approximately 9.7 billion in the next thirty years (United out a quali-quantitative assessment of the BVOC emissions generated by Nations DESA, 2022). The consequent broadening of urbanized areas in re- crop cultivation in an integrated rooftop greenhouse (i-RTG) that was sponse to an increasing number of inhabitants is driving the agricultural placed in the ICTA-UAB building (Sanjuan-Delmás et al., 2018). Following sector toward innovative and sustainable techniques for food production proposed strategies and previous works (European Union, 1994; Soria that prioritizes proximity to the city (Maye, 2019; Buscaroli et al., 2021; et al., 2015; Li et al., 2019; Tholl et al., 2021) BVOCs were collected in a Rao et al., 2022). Urban planning has also moved in the direction of a static enclosure with dynamic sampling technique and recovered with sol- more sustainable design by integrating vegetation into buildings vent extraction, identified, and quantified by gas chromatography coupled (Appolloni et al., 2021; Puppim de Oliveira et al., 2022), both for cultiva- mass spectrometry (GC–MS). Detected levels were compared with available tion and ornamental purposes, such as indoor farming (Sabeh, 2020; LCIs as main referencing values for indoor emissions and additionally Avgoustaki and Xydis, 2021; Banerjee et al., 2022) and vertical gardening BVOCs emission factor (EF) related to the different phenological stage (Orsini et al., 2020; HUI et al., 2022). was calculated throughout plants development. Finally, the performance Green installations have been reviewed for their positive effects on and the reproducibility of the overall sampling methodology performed building performance in terms of temperature and noise mitigation (Li was evaluated. et al., 2022; Oquendo-Di Cosola et al., 2022) and energy inputs (Muñoz- Liesa et al., 2021; Zambrano et al., 2021) and considered for their capability 2. Materials and methods to remove harmful volatile organic compounds (VOCs) from indoor spaces (Ysebaert et al., 2021) and decrease environmental carbon emissions 2.1. I-RTG arrangement and plant cultivation (Lampinen et al., 2022; Saeed Meo and Karim, 2022). However, many stud- ies on air assessment in the open field have reported the release of high bio- Green bean Phaseolous vulgaris L. ‘Pongo’ was cultivated in the genic volatile organic compounds (BVOCs) from plants (Laothawornkitkul southwest-facing greenhouse located inside the i-RTG of the ICTA-UAB re- et al., 2009; Calfapietra et al., 2013), mainly isoprene-based compounds, search institute (41°29′51.6″ N 2°06′31.2″ E, Fig. 1). Both i-RTG and build- and their chemical interaction with the tropospheric layer. Multiple chain ing specific configuration allow a constant exchange of environmental reactions occurring between BVOCs and air molecules may result in signif- flows among the spaces and, alternately, with outdoor flows according to icant increases in atmospheric GHGs (CO2, N2O, NOx, O3, CH4) and the programming of the façade system (Muñoz-Liesa et al., 2021) (Fig. 1). suspended organic aerosols (Cai et al., 2021; Mahilang et al., 2021; Crop cultivation was carried out in spring 2020 (February 12 to May 15). Dodman et al., 2022), reflecting air quality and climatic condition varia- The cultivation system was run hydroponically under drip fertigation tions (Fu et al., 2010; Peñuelas and Staudt, 2010; Glotfelty et al., 2016). and organized into 8 trailed lines of flanked perlite bags. A total of 256 Individuating large-scale effects dependent on plant emissions is de- seedlings of 10–15 cm height were transplanted with a plant spacing of manding, although it could be estimated via extended monitoring and 0.20 m × 0.40 m, resulting in a density of 15 plants per m2 (Fig. 2). The cul- real-time sampling of the urban and wild environment (for instance PTR- tivated area was approximately 40 m2 (Fig. 2). Plants were grown with a MS), or via prediction models (Guenther et al., 2006), which could show nutrient solution for leafy crops dissolved in rainwater. Water management particular trend distributions of biogenic fluxes (Chuang et al., 2011; Seco was controlled by a programmed irrigation system that was periodically ad- et al., 2015; Drewer et al., 2018; Coggon et al., 2021). In the city area the justed for the plants' daily requirements. Daily water pH and electric con- impact of BVOC emissions regarding green-integrated infrastructures was ductivity (EC) were measured in the delivered and leached solutions and already theorized (Niinemets and Peñuelas, 2008; Tiwari et al., 2019; in the collected rainwater to maintain an adequate nutritional supply. Am- Persiani, 2021), but currently research targeting the assessment of BVOC bient temperature, relative humidity, and radiation were constantly moni- levels in urban environments is limited (Yang et al., 2009; Zhang et al., tored (systems CS215, Campbell Scientific and L202, Hukseflux) by 2020). averaging 10-min time periods using dataloggers (models CR3000 and Indoors, safety levels and ventilation guidelines for anthropogenic and CR1000X, Campbell Scientific Inc., USA). Indoor cultivar requirements biogenic VOCs have been comprehensively wrapped up in harmonization were fulfilled via the movement of the façade, handled by an automated frameworks of the ECA-IAQ (European Union, 2020; European Union, station (Siemens Building Technologies Ltd). 2021). Based on recognized health procedures and according to collected monographs, report n°29 provides the lowest concentration of interest 2.2. Static enclosure design and setup (LCI) for a VOC that does not reproduce an adverse effect on human health after long-term exposure in a closed environment. With respect to BVOCs, Plant emissions were collected in a chamber, which was a static enclo- LCIs are fixed between 1400 and 5000 μg m−3 but individual levels were sure (Tholl et al., 2006) built alongside the crop inside the i-RTG (Fig. 3). determined only for few monoterpenes (α-pinene, β-pinene, 3-carene and Chamber dimensions were established following those of a previous test de- limonene) despite broad range of volatiles emitted by plants. With respect signed for preliminary emissions assessment (Stringari et al., 2022). The to the assessment strategies, different sampling techniques and important chamber consisted of a rectangular steel frame assembled and delimited elements to consider have been discussed (European Union, 1994), with low-density polyethylene (LDPE) cloth. The chamber was divided supporting user's choice of the most adequate sampling procedure. Since in- into two equal sections of 1000 L (0.35 m width × 0.85 m height × 3.50 m door BVOCs can accumulate, levels may exceed safety risk values and result length). The chamber remained open to the i-RTG ambient and was isolated in serious health issues related to breathing and hypersensitivity (Müller during the BVOC sampling process. In the right section, 12 seedlings were 2 G. Stringari et al. Science of the Total Environment 874 (2023) 162319 Fig. 1. Schematic reproduction of the environmental flow direction along the ICTA building, adapted from (Nadal et al., 2017). (A.1) and a planimetry of the 4th floor dedicated to urban agriculture, where current/the considered i-RTG is highlighted (A.2). transplanted into perlite bags distributed inside the section and grown (6 × 70 mm, 250 mg, 10/60 mesh, SKC) were placed upstream of the car- under the same environmental conditions as the i-RTG crop. The volume tridges to ensure adequate BVOC extraction. Air was collected from the cen- occupied by the single plant (0.0867 m3) was further applied in the calcu- ter of the chamber to represent its atmospheric composition. Since our lation of the EF of the detected volatiles. The left section remained empty purpose was the collection of the current environmental air stream in the to provide a representative sample of i-RTG ambient. Temperature, relative i-RTG, no air purging was performed inside the enclosure prior to sampling. humidity, and radiation inside the chamber were continuously recorded to For each sampling process, a total volume of 3.75 L of air was extracted dur- obtain supporting information regarding plant physiological status before ing a 15 min time period (airflow 0.25 L min−1). This term was decided and during the BVOC sampling process. In the empty section, only temper- after observing the environmental performance several times in the plant ature was monitored. section, considering the well-known influence of abiotic stress on the plant emission response (Ortega and Helmig, 2008), and focusing mainly 2.3. BVOC dynamic sampling on relative humidity, which usually showed the highest variation under ex- tended closure. The sampling period started 5 weeks after transplanting, en- Air BVOCs were extracted into charcoal cartridges (Anasorb® CSC, suring that the average stem size was above 30 cm (March 26 until May 8). 6 × 70 mm – 100/50 mg, SKC) using a controlled air stream (Electro Air samples were taken multiple times during individual phenological A.D. pump and flow meter E-7000 Series, Bronkhorst®). Drying tubes stages of the crop cycle (vegetative-reproductive-productive-senescent), in- dividuated by periodical stem sizing, blossom counting and biomass (fallen leaves and harvested fruits) weighing. Consecutive measurements were considered repetitions of a determined stage. Samples were obtained at or near the 12 AM time point, coinciding with the maximum plant activity (Loreto et al., 2006; Ortega et al., 2008). Additional air samples were ob- tained before the start of the experiment to control BVOCs in the i-RTG am- bient environment. Procedural blank samples were also analyzed to identify possible contamination during the analytical process. Fig. 2. Lateral view of the arrangement of the i-RTG cultivation (A.1) and a picture 2.4. Post-sampling analysis of the plant spacing along the substrate bags (A.2). 2.4.1. BVOC determination The collected sorbents were flushed with nitrogen to prevent BVOC ox- idation and then capped and stored at 4 °C before analysis. BVOC characterization focused on four of the compounds usually emit- ted by green beans (Table 1) and leafy plants (Holzke et al., 2006; Fu et al., 2010; Maffei, 2010; Malik et al., 2018) and representative of their chemical class. Qualitative and quantitative analysis was performed on monoterpene α-pinene and oxygenated monoterpene linalool, on sesquiterpene β- caryophyllene and on lipoxygenase derivate cis-3-hexenol following the NIOSH Method n. 1552 (NIOSH, 1996). Then, BVOCs were desorbed with 1 mL of carbon disulfide (CS2 for spectroscopy, ≥99.9 %, ACROS OR- GANIC) and transferred to 1.5 mL vials. Fig. 3. (A.1) Graphical setup of the chamber for volatile collection in the empty (i- Sample extracts and standard solutions were analyzed using a GC–MS RTG) and filled (12 plants) sections (sensors 1, 2 and 3 for temperature, relative system (TRACE 1300/1310 GC coupled to an ISQ7000 MS, Thermo Scien- humidity, and radiation; 4 is the BVOC sorbent + dryer tube); (A.2) Picture tific, USA). Extracts (2 μL) were injected in split-less mode (1 min, 240 °C), showing the air sampling. and BVOCs were separated using a TG-WAXMS capillary column 3 G. Stringari et al. Science of the Total Environment 874 (2023) 162319 Table 1 List of typical (bold text) and induced (*) BVOCs emitted by Phaseolus vulgaris L. retrieved from the literature (Croft et al., 1993; Ballhorn et al., 2008; Souza et al., 2013; Quintana-Rodriguez et al., 2015). BVOCs class Terpenoids LOX derivates (lypoxygenase) Shikimic acid derivates Photosynthesis derivates (glucose) Monoterpenes α-Pinene cis-3-Hexenol* Methyl salicylate* Methanol* β-Pinene* cis-3-Hexenal* Indole cis-β-Ocimene* trans-2-Hexenal* Limonene* trans-2-Hexenol* 1,8-Cineole* trans-3-Hexenal* Camphene trans-3-Hexenol* Linalool* (1-Hexanol)* Acetate (acetic acid)* Sesquiterpenes β-Caryophyllene cis-3-Hexenyl L-carveol* Acetate* cis-α-Bergamotene* 1-Octen-3-ol* α-Terpineol* 2-Ethylhexan-1-ol* Farnesene* Butyrate* cis-3-Hexenyl Homoterpenes trans-4,8-Dimethyl- Isovalerate* 1,3,7-Nonatriene* cis-Jasmone* Methyl jasmonate Others 2-Butanone* Nonanal* Decanal* (TraceGOLD™, 30 m × 0.32 mm × 1 μm, Thermo Scientific, USA) with a were cut at the stem base; the whole plant, stem, and leaves were weighed constant flow of 2.7 mL min−1 of He as carrier gas. Compounds were eluted to provide the average weight of fresh biomass. The 25 % of harvested using the following temperature gradient: initial temperature of 35 °C (for leaves was gently spread onto a scan surface, and the acquired image was 1 min), followed by 10 °C min−1 temperature ramp to a final temperature processed using an encoding Python 3.8 script (Spyder 4.1.5; full code in of 215 °C (held for 1 min). MS transfer line and ion source temperatures the Supplementary materials) that calculated the area of the leaves; the were set at 240 °C and 200 °C, respectively. Compounds were ionized at 100 % area was derived by relating the area to the corresponding biomass 70 eV and the resulting ions were detected in scan mode at 50–600 amu weight. The dry weight was also provided by drying the fresh biomass in a (0.2 scan s−1) for identification purposes. Compounds were identified by static oven (60–70 °C). The LAI calculation was derived by the ratio be- comparing their MS spectra with the NIST library (NIST 17 Mass Spectral tween the average leaf area calculated and the plant spacing in the i-RTG Library Software) using Chromeleon Studio 7.2 software (Thermo Scien- (0.20 m × 0.40 m). tific). Quantitation was led in timed selected ion monitoring (SIM) to im- prove instrument sensitivity and specificity. In SIM mode, compounds were identified by comparing the retention time with solutions containing 2.4.3. Statistical analyses and environmental correlation commercially available standard compounds. The lowest limit of quantita- The reproducibility of the carried-out sampling technique was exam- tion (LLOQ) of target BVOCs was assessed by injecting six replicates of the ined using statistical analyses to ensure the reliability of the results. Be- smallest standard solution (0.001 ng μL−1) detected (LOD), with a relative tween the two sections of the static enclosure, BVOC emissions were standard deviation (RSD%) ≤ 21 %. (Table 1 in the Supplementary mate- compared with paired tests (Wilcoxon signed-rank test). Similarly, environ- rials). BVOCs concentration (ng μL−1) in the samples was calculated mental conditions – temperature and relative humidity – monitored during using a calibration curve obtained with standards (0.001–0.1 ng μL−1). the closure time were compared with one-way test (ANOVA). In addition, the effect of the static enclosure was investigated by looking at significant 2.4.2. BVOC emission factor calculation Pearson correlations (r) between environmental variables (radiation, tem- Quantitative data obtained for the detected BVOCs were then applied to perature, and relative humidity) and individual BVOCs. Data processing the calculation of an EF, following (Li et al., 2019) Eq. (1) for a static enclo- was realized in R Studio (version 3.6.3). sure system: the EF (ng g−1 h−1) of a BVOC species (EFBVOC) is given by the difference between the total BVOC concentration (C, ng L−1) emitted by the plant and its concentration in the background air sample (C0) collected 3. Results in the static enclosure (V and V0, L) for the total time of enclosure (Δt), re- lated either to the plant (P) leaf area (m2), leaf area index (LAI), or fresh/ 3.1. Environmental performance inside the i-RTG during plant cultivation dry biomass (g). In our experiment, no background air sample was provided prior to sampling (no air purging) inside the enclosure. Therefore, the total Far from the sampling, the mean temperature registered over the crop BVOC concentration was correct on the blank samples collected. The de- cycle in the i-RTG and in the empty section of the static enclosure was rived equation was then simplified (Eq. (2)), giving the EFBVOC for the equivalent (18 °C and 19.5 °C, respectively) and slightly higher in the green bean plant. plant section (20 °C); this was also found between the mean relative humid- ity in the i-RTG (56 %) and in the plant section (54 %). The mean radiation C  V–C0  V0 measured at the crop level in the i-RTG and in the chamber was also similar EFBVOC ¼ (1) Δt  P (51.83 W m−2 and 47.90 W m-2, respectively). During air measurements, chamber temperature was higher in the plant section and on average CV 2.5 °C higher than in i-RTG; in contrast, relative humidity in the i-RTG EFBVOC ¼ (2) Δt  P was still higher than levels recorded in the plant section (+16 %), although these levels as well as for temperature ones were found to increase expo- The leaf area and biomass of the plants were measured periodically nentially along the time of enclosure (Fig. 4) with peaks close to the satura- along progressive growth stages. Specifically, four randomly chosen plants tion point. 4 G. Stringari et al. Science of the Total Environment 874 (2023) 162319 Fig. 4. Three representative records of temperature and relative humidity measured in the plant section during air sampling; exponential trendlines of relative humidity are highlighted. 3.2. Crop emission levels in the i-RTG show a significant difference between the collected emissions (lowest P value >0.36). Likewise, the environmental factors measured during collec- Throughout the cultivation cycle, the chemical profile of the collected tions were generally similar except for relative humidity, whose maximum emissions was extremely variable, ranging between 0.35 μg m−3 and and minimum values registered in the two sections were significantly dif- 29.87 μg m−3 (0.04–5.36 ppb) or not detected (below the LLOQ). The ferent (P < 0.001 and P < 0.01, respectively). The interpretation of such highest concentration of each detected BVOC was compared with the re- variations is addressed by the environmental load analysis in the following spective EU-LCI value (Table 2), which was defined only for α-pinene but section (Section 3.3). not for the rest of the compounds. Therefore, these levels were compared to the given values of the corresponding terpene class, except for the miss- ing values for cis-3-hexenol. All the investigated compounds were below 3.3. Environmental load analysis of BVOC emissions the most updated EU-LCI values. The collected emissions throughout the season are shown in Fig. 5. Considering BVOC abundance, monoterpene By computing individual BVOC emissions with the mean, minimum and α-pinene was the most abundant (1.33–29.87 μg m−3), followed by LOX maximum rates of the variables recorded (temperature, relative humidity, derivate cis-3-hexenol (2.13–20.64 μg m−3), oxygenated monoterpene lin- and radiation) in compiled matrices, significant correlations were detected alool (0.40–16.69 μg m−3) and sesquiterpene β-caryophyllene (Fig. 7). In both the empty and the plant sections, analogous negative corre- (0.35–0.61 μg m−3). Considering the BVOC distribution, cis-3-hexenol lations were found between LOX derivative cis-3-hexenol and temperature and linalool were typically detected throughout the season and in both sec- variation (P < 0.05); for this volatile, the same correlation was observed tions of the chamber; in contrast, α-pinene and β-caryophyllene were occa- with maximum relative humidity rates, although only in the plant section, sionally detected and more often in the empty section. Emissions as well as oxygenated monoterpene and sesquiterpene, linalool and β- differences between the two sections were highlighted by subtracting the caryophyllene (P < 0.01). In contrast, no correlations were found for the BVOC amount of the empty section from the section enclosing the plants monoterpene α-pinene. No relevant relation was underlined with radiation. (Fig. 6). Although remarkable negative and positive emission variations As a result of the computational matrix, a strong positive correlation among were observed for all the detected compounds, statistical analysis did not all the volatiles (P < 0.001) was also highlighted in both sections. Among the variables, significant negative correlations (P < 0.01) between relative humidity maxima and the different patterns of temperature were individu- ated but only in the plant section. Table 2 Compiled EU-LCI values, highest concentrations collected in the static enclosure over the crop cycle, and the instrument lowest limit of detection (LLOQ). 3.4. Emission factor of detected BVOCs throughout the crop cycle in the i-RTG Compound μg m−3 EU-LCI value Detected level LLOQ From the emissions collected in the plant section, the respective BVOC α-Pinene 2500 29.87 0.489 EFs were determined and related to the corresponding crop growing stage Linalool 1400a 16.69 0.391 according to phenological measurements (Table 3). General tendencies β-Caryophyllene 1400a 0.61 0.320 were marked, although exceptional levels were also observed. Emission cis-3-Hexenol – 20.64 0.449 bursts were associated with vegetative development completion, decreas- a This group includes all monoterpenes, sesquiterpenes and their oxygen-containing ing progressively during blossoming and fruit production until senescence, derivatives. which was characterized by the lowest EFs registered. 5 G. Stringari et al. Science of the Total Environment 874 (2023) 162319 Fig. 5. Total BVOC emissions (μg m−3) collected in the empty and plant sections of the chamber throughout the cultivation of the green beans in the i-RTG. 4. Discussion BVOC chemistry and environmental relationships, as well as plant activity, should thus be revised. For monoterpenes (α-pinene) and sesquiterpenes Throughout the cultivation cycle, all the green bean BVOCs selected (β-caryophyllene), release (Loreto et al., 2006) is typically driven by tem- were detected. In general, levels described by measured concentrations perature and characterized by high reactive bursts (Guenther et al., 2006; were found to be variable. Because the building façade's screening mecha- Materić et al., 2015), although release is much slower for sesquiterpenes nism altered the i-RTG radiation, the ozone impact on the total BVOCs col- (Duhl et al., 2008), which may lead to underestimations during sampling. lected was neglected. Concentrations of all investigated volatiles were Emission of oxygenated monoterpenes (linalool) and LOX derivatives (cis- much below ascribable EU-LCI values. Additionally, taking as a reference 3-hexenol) is also generally inductive, regulated by both biotic and abiotic the highest BVOC detected (29.87 μg m−3 or 0.0054 ppm), α-pinene, its factors (Niinemets et al., 2013; Jamloki et al., 2021), but rather stable and concentration was approximatively 15 folds lower than the Risk Value more persistent in the atmosphere than hydrocarbon terpenes. In the liter- (450 μg m−3 or 0.0803 ppm) calculated from long exposure studies (from ature, monoterpenes have been reported along the vegetative stage (Holzke 6 h to 5 days). Indeed, even when researchers were in the i-RTG for long pe- et al., 2006) to progressively decrease at plant maturity (Mozaffar et al., riods of time (e.g., during harvesting or greenhouse maintenance), their ex- 2018), while OMT and LOX compounds have been documented over the posure to emissions was mitigated by frequent ventilation via automated entire productive phase (Manco et al., 2021), which is consistent with the windows and the edifice structure itself, which can contribute to a fast emission rates measured. Frequent variations were tentatively explained emissions decrease. Nevertheless, the main phenological EFs derived by the environmental load analysis in the two sections (Section 3.3). Consid- underlined high emissions at vegetative development and variable or low ering plant section, general increase of temperature and relative humidity emissions over the progression of plant growth (Table 3). Individual during the sampling could be reasonably associated to plants physiological response (transpiration) to the enclosing (Heiden et al., 2015; Pérez-Priego et al., 2015; Soria et al., 2015) and were significantly related with detected emissions. However, negative correlations found between many of the vol- atiles and relative humidity, and in one case (cis-3-hexenol) with tempera- ture are in contrast with past findings and may be questionable. A possible explanation may be found in scrutinized analysis of the molecular pattern of VOCs in conditions of high humidity levels (Zhou et al., 2017). Though the combination of increased temperature and relative humidity may improve emission amount in the environment the different interaction be- tween individual BVOC and water molecules may also reduce substantially the total concentration of the volatiles (Kari et al., 2018).BVOC fluctuations observed between consecutive samplings could then be attributed to re- sulted environmental fluxes in the chamber misleading correct estimation of BVOC levels in the i-RTG. Unfortunately, assumptions verification re- quired additional analysis and eventually the monitoring of physiological parameters (e.g., CO2 rates, stomatal conductance, etc.) that in our experi- ment were not conducted. Nevertheless, the reproducibility of the sampling method was assessed. Validation was performed on the blank samples in which no BVOC was detected (levels below the LLOQ) and on the statistical tests on the collected emissions and the environmental records between the Fig. 6. BVOC emissions (μg m−3) variation after subtraction of the total emissions two sections of the static enclosure, where indeed no significant differences collected in the empty section from those collected in the plant section. were highlighted in either case. 6 G. Stringari et al. Science of the Total Environment 874 (2023) 162319 Fig. 7. Positive and negative Pearson's r correlations between environmental variables (mean, maximum and minimum relative humidity, and air temperature: RH_mean, RH_max, RH_min, AirT_mean, AirT_max, AirT_min) and individual BVOC classes (MT monoterpene, OMT oxygenated monoterpene, LOX lipoxygenase derivate and ST sesquiterpene) detected in the chamber during air sampling in the empty (A.1) and plant (A.2) sections; significant correlations P < 0.001, P < 0.01 and P < 0.05 are indicated by the symbols ‘***’, ‘**’ and ‘*’. Correlations with radiation data are omitted here since they are not significant in any of the cases. 5. Conclusions choice of the proper sampling strategy, we suggested dynamic sampling in static enclosure because of an easy-to-implement method for preliminary According to our findings, expected BVOC emissions released by a leafy screening of BVOC emissions, which can provide the indicative levels of crop in an i-RTG can be rationally contained considering low levels found in BVOC fluxes along a short cultivation cycle (4 months). The occurrence of a small fraction (1 m3) of it, and more dispersed in relation to traditional in- artifacts during the measurement leading to wrong estimation of current door systems due to recurrent turnovers of the air enclosed. Regarding the BVOC levels is still higher compared to most recent sampling technologies. 7 G. Stringari et al. Science of the Total Environment 874 (2023) 162319 Table 3 Agriculture (818002-URBAG), and the PALADYN Project (#834934). The Emission factors (average of nearby air measurements) of the reviewed BVOCs over publication reflects the author's views. The Research Executive Agency the crop cycle in the i-RTG, and the environmental factors, mean, maximum and (REA) is not liable for any use that may be made of the information minimum temperature (a, b, c) and relative humidity (A, B, C) most significantly cor- contained therein. related with them. BVOC EF (ng g−1 h−1) Appendix A. Supplementary data Plant phenological α-Pinene Linaloolb, A cis-3-Hexenola, b, c, A β-Caryophylleneb, A stage Supplementary data to this article can be found online at https://doi. Full vegetative 75.852 51.335 78.967 1.558 org/10.1016/j.scitotenv.2023.162319. 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