Volatile Organic Compounds Removal Efficiency Research Articles

Recent advances in volatile organic compounds abatement by catalysis and catalytic hybrid processes: A critical review

Air pollution, particularly for toxic and harmful compounds to humans and the environment, has aroused increasing public concerns. Among air pollutants, volatile organic compounds (VOCs) are the main sources of air pollution. Many attempts have been made to control VOCs using catalysts, plasma, photolysis, and adsorption. Among them, oxidative catalysis by noble metals or transition metal oxides is considered one of the most feasible and effective methods to control VOCs. This paper reviews the experimental achievements on the abatement of VOCs using noble metals, transition metals and modified metal oxide catalysts. Although the catalytic degradation of VOCs appears to be feasible, there are unavoidable problems when only catalysis treatments are applied to the field. Therefore, catalysts including hybrid processes are developed to improve the removal efficiency of VOCs. This review addresses new hybrid treatments to remove VOCs using catalysts, including hybrid treatment combined with plasma, photolysis, and adsorption. The mechanism of the oxidation of VOCs by catalysts is explained by adsorption-desorption principles, such as the Langmuir-Hinshelwood, Eley-Rideal, and Mars-van-Krevelen mechanisms. A π-backbonding interaction between unsaturated compounds and transition metals is introduced to better understand the mechanism of VOC removals. Finally, several factors affecting the catalytic activities, such as support, component ratio, preparation method, metal loading, and deactivation factor, are discussed.

Adsorption of Volatile Organic Compounds at Medium-High Temperature Conditions by Activated Carbons

Activated carbon (AC) adsorption is an effective method for abatement of volatile organic compounds (VOCs) in coal-fired power plants. The adsorption behaviors of VOCs (toluene and chlorobenzene) for ACs (coconut shell-based AC (CSAC) and wood-based AC (WAC)) under medium-high temperature (MHT: 90–150 °C) conditions were investigated in a fixed-bed reactor. The results indicated that the adsorption capacity of VOCs was reduced with increasing temperature. CSAC had a higher adsorption capacity and adsorption rate for the two VOCs than WAC at the same adsorption temperature. The adsorption capacity of toluene was within the range of 13.9–49.9 mg/g, while that for chlorobenzene was 26–80.3 mg/g. The content of oxygen-containing groups on the AC surface was increased with acid modification and decreased with alkali modification. The adsorption capacity of AC was improved to varying degrees after chemical modification. Adsorption was mainly controlled by physical adsorption, whereas the effects of chemisorption became evident with increasing temperature. The interactions between oxygen-containing groups and VOCs were more beneficial for improving adsorption capacity than π–π interactions. The pseudofirst-order kinetic model better described the adsorption of VOCs by ACs. The MHT conditions promoted the intraparticle diffusion; lower VOC concentration resulted in the external mass transfer of AC becoming the adsorption rate-limiting step. Increasing the external surface area and micropore volume of AC and enriching the content of surface oxygen-containing groups were useful in enhancing the VOC removal efficiency.

Potted plants do not improve indoor air quality: a review and analysis of reported VOC removal efficiencies.

Potted plants have demonstrated abilities to remove airborne volatile organic compounds (VOC) in small, sealed chambers over timescales of many hours or days. Claims have subsequently been made suggesting that potted plants may reduce indoor VOC concentrations. These potted plant chamber studies reported outcomes using various metrics, often not directly applicable to contextualizing plants' impacts on indoor VOC loads. To assess potential impacts, 12 published studies of chamber experiments were reviewed, and 196 experimental results were translated into clean air delivery rates (CADR, m3/h), which is an air cleaner metric that can be normalized by volume to parameterize first-order loss indoors. The distribution of single-plant CADR spanned orders of magnitude, with a median of 0.023 m3/h, necessitating the placement of 10-1000 plants/m2 of a building's floor space for the combined VOC-removing ability by potted plants to achieve the same removal rate that outdoor-to-indoor air exchange already provides in typical buildings (~1 h-1). Future experiments should shift the focus from potted plants' (in)abilities to passively clean indoor air, and instead investigate VOC uptake mechanisms, alternative biofiltration technologies, biophilic productivity and well-being benefits, or negative impacts of other plant-sourced emissions, which must be assessed by rigorous field work accounting for important indoor processes.

Efficient photodegradation of volatile organic compounds by iron-based metal-organic frameworks with high adsorption capacity

The efficient removal of volatile organic compounds (VOCs) is still challenging, and suitable strategies and auxiliary materials are lacking. Herein, we propose a highly efficient and stable iron-based metal-organic framework (Fe-MOF) in which the adsorption removal and photodegradation regeneration step alternate to realize repeatable and efficient removal of VOCs. A group of morphology-controlled Fe-MOFs serves as both the adsorbent and photocatalyst under ambient conditions to remove typical VOCs, e.g., toluene by relying on their high porosity and catalytic activity. The optimized Fe-MOF exhibits 100% adsorption removal efficiency for a toluene concentration of 460 ppm, and the Fe-MOF could be regenerated by converting the adsorbed toluene into harmless CO2 under 1 SUN (100 mW/cm2) solar irradiation. More importantly, the Fe-MOF showed excellent durability during repeated adsorption and degradation processes for 100 cycles.

The botanical biofiltration of VOCs with active airflow: is removal efficiency related to chemical properties?

Botanical biofiltration using active green walls is showing increasing promise as a viable method for the filtration of volatile organic compounds (VOCs) from ambient air; however there is a high level of heterogeneity reported amongst VOC removal efficiencies, and the reasons for these observations have yet to be explained. Comparisons of removal efficiencies amongst studies is also difficult due to the use of many different VOCs, and systems that have been tested under different conditions. The current work describes a procedure to determine whether some of these differences may be related to the chemical properties of the VOCs themselves. This work used an active green wall system to test the single pass removal efficiency (SPRE) of nine different VOCs (acetone, benzene, cyclohexane, ethanol, ethyl acetate, hexane, isopentane, isopropanol and toluene) and explored which chemical properties were meaningful predictor variables of their biofiltration efficiencies. Ethanol was removed most efficiently (average SPRE of 96.34% ± 1.61), while benzene was least efficiently removed (average SPRE of 19.76% ± 2.93). Multiple stepwise linear regression was used to determine that the dipole moment and molecular mass were significant predictors of VOC SPRE, in combination accounting for 54.6% of the variability in SPREs amongst VOCs. The octanol water partition coefficient, proton affinity, Henry's law constant and vapour pressure were not significant predictors of SPRE. The most influential predictor variable was the dipole moment, alone accounting for 49.8% of the SPRE variability. The model thus allows for an estimation of VOC removal efficiency based on a VOC's chemical properties, and supports the idea that system optimisation could be achieved through methods that promote both VOC partitioning into the biofilter's aqueous phase, and substrate development to enhance adsorption.'

Removal of volatile organic compounds in a pilot-scale biocover installed in a municipal waste landfill

A pilot-scale biocover was installed at a sanitary landfill for municipal waste, and the removal of volatile organic compounds (VOCs) by the biocover was evaluated for a long period of 550 days. The biocover (2.5 m W × 5 m L × 1 m H) was constructed with the mixture of soil, perlite, earthworm cast and compost (6:2:1:1, v/v). The total VOCs concentration of the inlet gas into the biocover was 820.3 ppb~7,217.9 ppb, and the total VOCs concentration of the outlet gas from the surface of the biocover was 12.6 ppb~1,270.1 ppb. The average removal efficiency of total VOCs was 87.6 ± 11.0% (60.5% for minimum and 98.5% for maximum). Toluene concentration was the highest among the inlet VOCs, followed by ethylbenzene, m, p-xylene and o-xylene. These aromatic VOCs accounted for more than 50% of the total VOCs concentration. Other than these aromatic VOCs, hexane, cyclohexane, heptane, benzene, and acetone were major VOCs among the inlet VOCs. Compared with the VOC profiles in the inlet gas, the relative contribution of dichloromethane to the outlet VOCs emitted from the biocover layer increased from 0.1% to 15.3%. The average removal efficiencies of BTEX in the biocover were over 84% during the operation period of 550 days. The average removal efficiencies of hexane, cyclohexane and heptane in the biocover were 86.0 ± 18.9%, 85.4 ± 20.4% and 97.1 ± 4.0%, respectively. The removal efficiency of VOCs in the biocover decreased not only when the ambient temperature had fallen below 5oC, but also when the ambient temperature had risen above 23oC. Information on the VOCs removal characteristics of the biocover installed in the landfill field can be useful for commercializing the biocover technology for the treatment of VOCs.

The effect of ionization energy and hydrogen weight fraction on the non-thermal plasma volatile organic compounds removal efficiency

The degree of difficulty of volatile organic compounds (VOCs) degradation in non-thermal plasma (NTP) related to their chemical structures, ionization potentials and hydrogen weight fraction was investigated. Benzene, methylbenzene, xylene, n-pentane, n-hexane, cyclohexane, ethyl acetate, ethyl propionate, ethyl butyrate, propanone, 2-butanone and 2-pentanone, total 12 VOCs were chosen as the typical VOC agents from the four main types of VOCs such as aromatic hydrocarbons, alkanes, ketones and esters with different structures and ionization potentials. The experimental results indicate that the ionization potential is a parameter indicating the destruction efficiency of VOCs by NTP. It is a trend that the higher the ionization potentials are, the weaker the reactivity of VOCs and radicals, and the more difficult it is to destroy VOCs at the same initial VOC concentration and the specific input energy. The influence of hydrogen weight fraction on the decomposition efficiency is different from the ionization potential one’s. For aromatic hydrocarbons, ketones and esters, the higher removal efficiency is observed with the higher percentage of hydrogen; for alkanes, the situation is just the opposite. It is indicated that this exceptional situation relates to chemical structures of VOCs. Their chemical structures make the trend of the relation of VOCs degradation efficiency on the ionization potentials appear a deviation.

Performance of various commercial TiO2 in photocatalytic degradation of a mixture of indoor air pollutants: Effect of photocatalyst and operating parameters

Photocatalytic oxidation (PCO) air cleaners can be installed in air handling units to reduce occupants’ exposure to hazardous gases, boost indoor air quality, and concomitantly lower HVAC energy consumption by lowering the required ventilation rate. In this work, photocatalytic activity of four commercialized titanium dioxide photocatalysts (P25, PC500, UV100, and S5-300A) for treating a mixture of seven prevalent volatile organic compounds (VOCs) were assessed in a continuous flow reactor. The impacts of major experimental factors, namely concentration (15–100 ppb), relative humidity level (0–60% at 23°C), and residence time (0.012–0.05 s), on the removal efficiency and by-products generation were examined. Photocatalysts were characterized by X-ray diffraction (XRD), nitrogen adsorption–desorption, Fourier transform infrared (FTIR), and scanning electron microscopy (SEM). UV100 possessed the highest values for total VOC removal efficiency, which could be attributed to its large surface area, high porosity, good crystallinity, and large population of surface hydroxyls. Regarding relative humidity, two dominant trends were found: i) increasing the humidity resulted in lower removal efficiencies or ii) existence of an optimum humidity level in some cases. The treatment efficiency followed the order: alcohols > ketones > aromatics > alkanes. The main by-products in the gas phase were formaldehyde, acetaldehyde, acetone, and propionaldehyde.

KOH activated pine tree needle leaves biochar as effective sorbent for VOCs in water

The removal of volatile organic compounds (VOCs) from water using KOH-activated pine tree needle leaves biochar is considered a cost effective and efficient process. In this study, pine tree needle leaves were mixed with 0, 50, 100 and 200% (KOH weight/feedstock weight) of KOH, respectively. Then, the mixture was pyrolyzed at 500 degree celcius for 6 hrs. The adsorption characteristics of 10 VOCs to the biochar were tested. The results indicated that the removal efficiency of the KOH activated biochar was highest in 100% KOH-biochar. The VOC removal efficiencies of 50% and 200% KOH activated biochar were similar and the 0% KOH activated biochar showed the lowest VOC removal. The FTIR results showed that increasing the amount of KOH seemed to enhance the formation of various functional groups, such as -OH, -C=C, -O. The adsorption strength of 10 VOCs to the KOH activated biochar seemed to be increasing by the increase of the solubility of VOCs. This may suggest that the adsorption is taking place in hydrophilic sites of the biochar surface. The KOH activated pine tree needle leaves biochar can be an effective sorbent for VOCs removal in water and 100% KOH mixing seemed to provide better sorption capacity.

Prospective application of melanized fungi for the biofiltration of indoor air in closed bioregenerative systems.

Cultures of melanized fungi representative of the black yeast orders Capnodiales (Cladosporium cladosporioides and Neohortaea acidophila) and Chaetothyriales (Cladophialophora psammophila) were confined with indoor air from the laboratory during 48 h. Volatile organic compounds (VOCs) from the headspace were analyzed by thermal desorption gas chromatography time-of-fly mass spectrometry (TD-GC-ToFMS, detection threshold 0.1 μg m-3) and compared against an abiotic control. A mixture of 71 VOCs were identified and quantified in the indoor air (total concentration 1.4 mg m-3). Most of these compounds were removed in the presence of fungal biomass, but 40 newly formed putative volatile metabolites were detected, though at comparatively low total concentrations (<50 μg m-3). The VOCs emission profile of C. cladosporioides, a ubiquitous and well-known species often associated to the sick building syndrome, was consistent with previous literature reports. The specialized C. psammophila and N. acidophila, isolated respectively from gasoline polluted soil and from lignite, displayed rather specific VOCs emission profiles. Mass balances on the fungal uptake and generation of VOCs resulted in overall VOCs removal efficiencies higher than 96% with all tested fungi. Applied aspects and biosafety issues concerning the suitability of black yeasts for the biofiltration of indoor air have been discussed.

Active {001} Facet Exposed TiO2 Nanotubes Photocatalyst Filter for Volatile Organic Compounds Removal: From Material Development to Commercial Indoor Air Cleaner Application.

TiO2 nanotubes (TNT) have a highly ordered open structure that promotes the diffusion of dioxygen and substrates onto active sites and exhibit high durability against deactivation during the photocatalytic air purification. Herein, we synthesized {001} facet-exposed TiO2 nanotubes (001-TNT) using a new and simple method that can be easily scaled up, and tested them for the photocatalytic removal of volatile organic compounds (VOCs) in both a laboratory reactor and a commercial air cleaner. While the surface of TNT is mainly composed of {101} facet anatase, 001-TNT's outer surface was preferentially aligned with {001} facet anatase. The photocatalytic degradation activity of toluene on 001-TNT was at least twice as high as that of TNT. While the TNT experienced a gradual deactivation during successive cycles of photocatalytic degradation of toluene, the 001-TNT did not exhibit any sign of catalyst deactivation under the same test conditions. Under visible light irradiation, the 001-TNT showed degradation activity for acetaldehyde and formaldehyde, while the TNT did not exhibit any degradation activity for them. The 001-TNT filter was successfully scaled up and installed on a commercial air cleaner. The air cleaner equipped with the 001-TNT filters achieved an average VOCs removal efficiency of 72% (in 30 min of operation) in a 8-m3 test chamber, which satisfied the air cleaner standards protocol (Korea) to be the first photocatalytic air cleaner that passed this protocol.

Application Study on Three-Bed Regenerative Thermal Oxidizers to Treat Volatile Organic Compounds

Organic solvents with different volatilities are widely used in various processes and generate air and water pollution problems. One of the popular treatment processes for volatile organic compounds (VOCs) is regenerative thermal oxidation for the high destruction and removal efficiency. In this paper, the authors presents a project case dealing with VOCs, the waste gas with triethylamine and N-butylamine is disposed by a three-bed RTO treatment process. Two novel strategies were used in this project compared with the conventional RTO systems. Firstly, heat storage materials are saddle-shaped honeycomb, which could reform the distribution of waste gas flow in the saddle area and improve the efficiency of heat exchange. Secondly, the control mode of quick-opening valve is exhaust temperature control method instead of the time interval. The operation data shows that more than 99% of destruction and removal efficiency of VOC is obtained with slightly-level natural gas consumption. This research could provide a practical basis for the design of a RTO system.

Preparation and analysis of zero gases for the measurement of trace VOCs in air monitoring

Abstract. Air quality observations are performed globally to monitor the status of the atmosphere and its level of pollution and to assess mitigation strategies. Regulations of air quality monitoring programmes in various countries demand high-precision measurements for harmful substances often at low trace concentrations. These requirements can only be achieved by using high-quality calibration gases including high-purity zero gas. For volatile organic compound (VOC) observations, zero gas is defined as being hydrocarbon-free and can be, for example, purified air, nitrogen or helium. It is essential for the characterisation of the measurement devices and procedures, for instrument operation as well as for calibrations. Two commercial and one self-built gas purifiers were tested for their VOC removal efficiency following a standardised procedure. The tested gas purifiers included one adsorption cartridge with an inorganic media and two types of metal catalysts. A large range of VOCs were investigated, including the most abundant species typically measured at air monitoring stations. Both catalysts were able to remove a large range of VOCs whilst the tested adsorption cartridge was not suitable to remove light compounds up to C4. Memory effects occurred for the adsorption cartridge when exposed to higher concentration. This study emphasises the importance of explicitly examining a gas purifier for its intended application before applying it in the field.

Screening Foliage Plants for Indoor Air Pollution Abatement

Indoor air pollution is a major environmental health problem affecting people in both developed and developing countries. The use of houseplants is one of the emerging methods for abatement of indoor air pollution. Plants can remove indoor air pollutants by stomatal uptake, absorption and adsorption to plant surfaces. Indoor air characteristically contains a large consortium of volatile organic compounds (VOCs), such as formaldehyde, benzene and toluene. The volatile tested in this study toluene, is commonly found in buildings. The main objective of this project was to find the removal efficiency of toluene by four plant species, Aglaonema spp., Dracaena deremensis, Hedera helix and Chlorophytum comosum. This main goal was achieved by constructing a sealed closed chamber resembling the indoor environment in order to find the activity of selected indoor plants to the indoor air pollutant toluene. The concentration of introduced toluene was measured through gas-chromatography mass spectrometry (GC/MS). The possible causes for the differences in removal of toluene among selected plant species were determined by studying leaf morphology, stomatal numbers, plant physiology and growth related parameters. The removal efficiency, expressed on percentage level using toluene peak areas of the GCMS analyses varied among plant species. H. helix had the highest toluene removal percentage per plant over 24 hours (91.1%) followed by D. deremensis (75.0%), A. spp. (60.5%) and C. comosum (47.9%). The study found that stomatal index and stomatal pore length play a key role in VOC removal and that there was a positive relationship between stomatal conductance with toluene removal potential. Based on the results it can be further concluded that thickness of the cuticle is a hindrance to VOC penetration. In addition VOC removal is higher in plants having high photosynthetic rates and there was no relationship of leaf area with the VOC removal capacity. Further studies focusing on screening additional plant species for superior VOC removal efficiencies are warranted. Keywords: Indoor air pollution, Volatile organic compounds, Gas-chromatography Mass spectrometry, Stomatal conductance

Phytoremediation of volatile organic compounds by indoor plants: a review

Air quality in homes, offices, and other indoor spaces has become a major health, economic, and social concern. A plant-based removal system for volatile organic compounds (VOCs) appears to be a low-cost, environment-friendly solution for improving indoor air quality. This review presents and assesses VOC removal mechanisms that use plants and their associated microorganisms as well as the factors that influence the rate and efficiency of VOC removal. To increase removal efficiency, it is important to have a thorough understanding of the mechanisms of VOC degradation by plants and their associated microorganisms. The potential of plants and their associated microorganisms, whether present in pots or forced-air systems, to remove VOCs from indoor environments have been supported by a number of studies. Variations in removal efficiency depend on the plant species used, the chemical properties of the volatiles in question, and a cross-section of other internal and external factors. It is thus critical to select the right plants and use methods that reflect in vivo conditions. Indoor plants with superior air-purifying abilities have been extensively studied; however, the low rates of VOC removal efficiency in interior environments entail the need of more studies. For instance, factors that modulate VOC removal by plants, such as air circulation rate, light intensity, moisture status, and season need to be explored. Improving the efficiency of plants and their associated microorganisms for VOC remediation of indoor air is necessary to ensure sustainable and healthy indoor environments.

Photolysis and photooxidation of typical gaseous VOCs by UV Irradiation: Removal performance and mechanisms

Photodegradation by ultraviolet irradiation (UV) is increasingly applied in volatile organic compound (VOC) and odor gas treatments. In this study, 27 typical VOCs, including 11 hydrocarbons and 16 hydrocarbon derivatives, at 150–200 ppm in air and nitrogen gas were treated by a laboratory-scale UV reactor with 185/254 nm irradiation to systematically investigate their removal and conversion by UV irradiation. For the tested 27 VOCs, the VOC removal efficiencies in air were within the range of 13%–97% (with an average of 80%) at a retention time of 53 s, which showed a moderate positive correlation with the molecular weight of the VOCs (R = 0.53). The respective contributions of photolysis and photooxidation to VOC removal were identified for each VOC. According to the CO2 results, the mineralization rate of the tested VOCs was within the range of 9%–90%, with an average of 41% and were negatively correlated to the molecular weight (R = −0.63). Many of the tested VOCs exhibited high concentration particulate matters in the off-gases with a 3–283 mg/m3 PM10 range and a 2–40 mg/m3 PM2.5 range. The carbon balance of each VOC during UVirradiation was analyzed based on the VOC, CO2 and PM10 concentrations. Certain organic intermediates and 23–218 ppm ozone were also identified in the off-gases. Although the UV technique exhibited a high VOC removal efficiency, its drawbacks, specifically low mineralization, particulate matters production, and ozone emission, must be considered prior to its application in VOC gas treatments.

Volatile organic compounds (VOCs) removal in non-thermal plasma double dielectric barrier discharge reactor

Non-thermal plasma (NTP) an emerging technology to treat volatile organic compounds (VOCs) present in unhygienic point source air streams. In present study, double dielectric barrier discharge (DDBD) reactors were used for the first time to evaluate the removal efficiency of VOCs mixture of different nature at constant experimental conditions (input power 16–65.8 W, VOCs mixture feeding rate 1–6 L/min, 100–101 ppm inlet concentration of individual VOC). Reactor A and B with discharge gap at 6 mm and 3 mm respectively, were used in current study. When treated at an input power of 53.7 W with gas feeding rate of 1 L/min in DDBD reactor A, removal efficiency of the VOCs were: tetrachloroethylene (100%), toluene (100%), trichloroethylene (100%), benzene (100%), ethyl acetate (100%) and carbon disulfide (88.30%); whereas in reactor B, the removal efficiency of all VOCs were 100%. Plasma-catalyst (Pt-Sn/Al2O3, BaTiO3 and HZSM-5) synergistic effect on VOCs removal efficiency was also investigated. Highest removal efficiency i.e 100% was observed for each compound with BaTiO3 and HZSM-5 at an input power 65.8 W. However, integrating NTP with BaTiO3 and HZSM-5 leads to enhanced removal performance of VOCs mixture with high activity, increase in energy efficiency and suppression of unwanted byproducts.

Volatile Organic Compound Removal Efficiency of Green and Variegated Foliage Plants Grown under Different Light Intensities

Volatile Organic Compound Removal Efficiency of Green and Variegated Foliage Plants Grown under Different Light Intensities

Volatile organic compounds absorption in packed column: theoretical assessment of water, DEHA and PDMS 50 as absorbents

A fixed volume packed column was simulated for the absorption at counter-current of four more or less hydrophobic volatile organic compounds (VOCs) in water and in two heavy organic solvents (PDMS 50, a silicone oil) and DEHA (Bis(2-ethylhexyl) adipate). Reliable values of the mass-transfer coefficients were deduced allowing to calculate the VOCs removal efficiency. Disappointing performances in heavy solvents, lower than 60% for isopropanol and acetone, were computed in a 3m height column and using mild conditions (atmospheric pressure and a liquid-to-gas mass flow rate ratio around 2). However, toluene removal efficiencies higher than 90% were simulated.

Suitability of Test Chambers for Analyzing Air Pollutant Removal by Plants and Assessing Potential Indoor Air Purification

A unique test chamber system, which enables experiments with plants under highly controlled environmental conditions, was used to examine the pollutant removal efficiency of plants. For this purpose, the removal of two different volatile organic compounds (VOC) (toluene, 2-ethylhexanol) from the air by aerial plant parts of two common indoor plant species (Dieffenbachia maculata and Spathiphyllum wallisii) was monitored. While the control over environmental conditions (temperature, relative humidity, CO2 content, and light condition) worked very well in all experiments, control experiments with the empty chamber revealed high losses of VOC, especially 2-ethylhexanol, over the test duration of 48 h. Nonetheless, compared to the empty chamber, a significantly stronger and more rapid decline in the toluene as well as in the 2-ethylhexanol concentrations was observed when plants were present in the chamber. Interestingly, almost the same VOC removal as by aerial plant parts could be achieved by potting soil without plants. A comparative literature survey revealed substantial heterogeneity in previous results concerning the VOC removal efficiency of plants. This can be mainly attributed to a high diversity in experimental setup. The experimental setup used in the current study offers an excellent opportunity to examine also plant physiological responses to pollutant exposure (or other stressors) under highly controlled conditions. For the analysis of VOC removal under typical indoor conditions, to obtain data for the assessment of realistic VOC removal efficiencies by plants in rooms and offices, a guideline would be helpful to achieve more coherent findings in this field of research.