Source apportionment of volatile organic compounds in Hong Kong homes

Indoor volatile organic compound (VOC) data obtained in 100 Hong Kong homes were analyzed to investigate the nature of emission sources and their contributions to indoor concentrations. A principal component analysis (PCA) showed that off-gassing of building materials, household products, painted wood products, room freshener, mothballs and consumer products were the major sources of VOCs in Hong Kong homes. The source apportionments were then evaluated by using an absolute principal component scores (APCS) technique combined with multiple linear regressions. The results indicated that 76.5 ± 1% (average ± standard error) of the total VOC emissions in Hong Kong homes attributes to the off-gassing of building materials, followed by the room freshener (8 ± 4%), household products (6 ± 2%), mothballs (5 ± 3%) and painted wood products (4 ± 2%). Analysis on the source strength in the monitored homes revealed that although six indoor sources were identified and quantified in the Hong Kong homes, only some homes were responsible for the elevated concentrations of target VOCs emitted from these sources. The findings provide us the mechanism of reducing levels of indoor VOCs and ultimately lead to cost effective reduction in population exposures.     

The effect of wet film thickness on VOC emissions from a finishing varnish

Finishing varnishes, a typical type of oil-based varnishes, are widely used to shine metal, wood trim and cabinet surfaces in Hong Kong. The influence of wet film thickness on volatile organic compound (VOC) emissions from a finishing varnish was studied in an environmental test chamber. The varnish was applied on an aluminium foil with three different wet film thickness (35.2, 69.9 and 107.3 microm). The experimental conditions were 25.0 degrees C, 50.0% relative humidity (RH) with an air exchange rate of 0.5 h(-1). The concentrations of the major VOCs were monitored for the first 10 h. The air samples were collected by canisters and analysed by gas chromatography/mass selective detector (GC/MSD). Six major VOCs including toluene, chlorobenzene, ethylbenzene, m,p-xylene, o-xylene and 1,3,5-trimethylbenzene were identified and quantified. Marked differences were observed for three different film thicknesses. VOC concentrations increased rapidly during the first few hours and then decreased as the emission rates declined. The thicker the wet film, the higher the VOC emissions. A model expression included an exponentially decreasing emission rate of varnish film. The concentration and time data measured in the chamber were used to determine the parameters of empirical emission rate model. The present work confirmed that the film thickness of varnish influenced markedly the concentrations and emissions of VOCs.     

Impact of Early Stage Incomplete Mixing on Estimating VOC Emissions in Small Test Chambers

Abstract Most of the existing emission models developed from small-scale chamber tests assume complete mixing in the chamber throughout the test period. This paper examined this assumption using a Computational Fluid Dynamics (CFD) model. The model simulated the three-dimensional air velocity profiles and Volatile Organic Compound (VOC) concentration distributions from wood stain in a well-designed mixing chamber of 1.0X0.8X0.5 m³. The model used measured data to determine the time-dependent VOC surface concentrations of wood stain. The CFD results show that the VOC concentrations in the test chamber were not uniform in the early stage (about 18 minutes). The first-order decay model using the complete mixing assumption will underestimate the Total VOC (TVOC) emission rates by 65% and 59% in the first 3 minutes and next 15 minutes, respectively. Since wood stain emitted about one third of the VOCs in the first 18 minutes, the impact of incomplete mixing in the early period is significant for calculating the material emissions. Furthermore, the mass transfer coefficient of TVOC calculated by CFD is also compared with that calculated by analogue theory and that calculated by experimental correlation.     

Heterogeneous photocatalytic removal of toluene from air on building materials enriched with TiO2

This paper reports the potential of heterogeneous photocatalysis as an advanced oxidation technology for removal of toluene from air using TiO₂ as a photocatalyst in building materials. First, the photocatalytic activity of two types of TiO₂ containing building materials, i.e. roofing tiles and corrugated sheets, has been investigated at ambient conditions (T=25.0 °C; relative humidity RH=47%; toluene inlet concentration [TOL]_in=17–35 ppbv). Toluene removal efficiencies up to 63% were observed at a gas residence time (τ) of 17 s. Second, the effect of RH (1–77%), [TOL]_in (23–465 ppmv) and τ (17–115 s) on toluene removal has been systematically investigated using TiO₂ containing roofing tiles as photocatalytic building materials. Results revealed lower toluene removal efficiencies at higher RH and [TOL]_in, whereas a positive effect was observed with increased τ. Under optimal conditions, toluene removal efficiencies up to 78±2% and elimination rates higher than 100 mg h⁻¹ m⁻² roofing tile were obtained. A decline in photocatalytic activity by a factor of 2 was observed after operation at gas residence times shorter than 69 s and [TOL]_in higher than 76 ppmv. Washing the building materials with deionized water, simulating rainfall, could partially (i.e. by a factor 1.3) regenerate the catalyst activity.     

Experimental evaluation of the growth rate of mould on finishes for indoor housing environments: Effects of the 2002/91/EC directive

We report the results of a study to evaluate the growth rate of three species of mould on plasters, finishes and paints typically used in structures with heavy weight building envelopes. The aim was to determine the influence of the chemical composition (in terms of organic fraction of the materials) on the growth rate of moulds. The study was carried out in the following steps: – characterization of materials; – inoculation of mould spores (3 species) on 7 types of material (2 plasters, 3 finishes, 2 paints); – growth in a climatic chamber (23 °C and 90% RH); – analysis of the mould growth rate using various experimental techniques (fluorescence microscopy analysis, thermogravimetric analysis, etc.). Results show a clear correlation between the organic substances contained in paints, plasters and finishes and the growth rate of the mould.     

UV-PCO device for indoor VOCs removal: Investigation on multiple compounds effect

Current design models for ultraviolet photocatalytic oxidation (UV-PCO) devices often assume that the air contains only one volatile organic compound (VOC) species or all the VOCs in the air can be treated on a non-interacting basis. However, trace-level multiple VOCs co-exist in most indoor environments. This paper assesses the significance of interference effects among different VOCs for indoor applications by full-scale “pull-down” experiments assisted with model simulations. Multiple versus single VOC tests were performed on selected groups of compounds under low concentration levels. Removal efficiency for each compound was calculated. It was found that the interference effect among test VOCs were generally small in the 2-VOC and 3-VOC mixture tests performed on toluene, ethylbenzene, octane, decane and dodecane with initial concentration of approximate 1 mg/m³ for each compound. However, in the 16 VOC mixture test, the interference effect among different VOCs became quite obvious, and compounds with lower removal efficiency in the single compound test appeared to also have relatively lower efficiency and more obvious delay period in the initial reaction. The L–H model appears to be able to account for this effect if reaction rate constants can be accurately estimated. Results, although limited, indicate that interference between multiple VOCs may not be neglected for the PCO reactor for indoor applications where the number of VOCs species is large and the TVOC concentration is high.     

Degradation of C2-C15 volatile organic compounds in a landfill cover soil

The composition of non-methane volatile organic compounds (hereafter VOCs) in i) the cover soil, at depths of 30, 50 and 70 cm, and ii) gas recovery wells from Case Passerini landfill site, (Florence, Italy) was determined by GC-MS. The study, based on the analysis of interstitial gases sampled along vertical profiles within the cover soil, was aimed to investigate the VOC behaviour as biogas transits from a reducing to a relatively more oxidizing environment. A total of 48 and 63 different VOCs were identified in the soil and well gases, respectively. Aromatics represent the dominant group (71.5% of total VOC) in soil gases, followed by alkanes (6.8%), ketones (5.7%), organic acids (5.2%), aldehydes (3.0%), esters (2.6%), halogenated compounds (2.1%) and terpenes (1.3%). Cyclics, heterocyclics, S-bearing compounds and phenols are ≤ 1%. In the wells the VOC composition is characterized by higher concentrations of cyclic (7.6%) and S-bearing compounds (2%) and lower concentrations of O-bearing compounds. The vertical distribution of VOCs in the cover soil shows significant variations: alkanes, aromatics and cyclics decrease at decreasing depth, whereas an inverse trend is displayed by the O-bearing species. Total VOC and CH₄ concentrations at a depth of 30 cm in the soil are comparable, inferring that microbial activity is likely affecting VOCs at a very minor extent with respect to CH₄. According to these considerations, to assess the biogas emission impact, usually carried out on the sole basis of CO₂ and CH₄ emission rates, the physical-chemical behaviour of VOCs in the cover soil, regulating the discharge of these highly contaminant compounds in ambient air, has to be taken into account. The soil vertical distribution of these species can be used to better evaluate the efficiency of oxidative capability of intermediate and final covers.     

Factors controlling volatile organic compounds in dwellings in Melbourne,Australia

This study characterized indoor volatile organic compounds (VOCs) and investigated the effects of the dwelling characteristics, building materials, occupant activities, and environmental conditions on indoor VOC concentrations in 40 dwellings located in Melbourne, Australia, in 2008 and 2009. A total of 97 VOCs were identified. Nine VOCs, n‐butane, 2‐methylbutane, toluene, formaldehyde, acetaldehyde, d‐limonene, ethanol, 2‐propanol, and acetic acid, accounted for 68% of the sum of all VOCs. The median indoor concentrations of all VOCs were greater than those measured outdoors. The occupant density was positively associated with indoor VOC concentrations via occupant activities, including respiration and combustion. Terpenes were associated with the use of household cleaning and laundry products. A petroleum‐like indoor VOC signature of alkanes and aromatics was associated with the proximity of major roads. The indoor VOC concentrations were negatively correlated (P < 0.05) with ventilation. Levels of VOCs in these Australian dwellings were lower than those from previous studies in North America and Europe, probably due to a combination of an ongoing temporal decrease in indoor VOC concentrations and the leakier nature of Australian dwellings.     

Estimating the effects of ambient conditions on the performance of UVGI air cleaners

Ultraviolet germicidal irradiation (UVGI) uses UVC radiation produced by low pressure mercury vapor lamps to control biological air contaminants. Ambient air velocity and temperature have a strong effect on lamp output by influencing the lamp surface cold spot temperature. In-duct UVGI systems are particularly susceptible to ambient effects due to the range of velocity and temperature conditions they may experience. An analytical model of the effect of ambient conditions on lamp surface temperature was developed for three common lamp types in cross flow from a convective–radiative energy balance assuming constant surface temperature. For one lamp type, a single tube standard output lamp, UVC output and cold spot temperature data were obtained under typical in-duct operating conditions. Over an ambient temperature range of 10–32.2 °C and an air velocity range of 0–3.25 m/s, measured cold spot temperature varied from 12.7 to 41.9 °C and measured lamp output varied by 68% of maximum. Surface temperatures predicted by the heat transfer model were 6–17 °C higher than corresponding measured cold spot temperatures, but were found to correlate well with cold spot temperature via a two-variable linear regression. When corrected using this relationship, the simple model predicted the cold spot temperature within 1 °C and lamp UVC output within ±5%. To illustrate its practical use, the calibrated lamp model was employed in a simulation of the control of a contaminant in a single-zone ventilation system by an in-duct UVGI device. In this example, failure to account for the impact of ambient condition effects resulted in under-prediction of average space concentration by approximately 20% relative to a constant output system operating at maximum UVC output.     

Properties of concrete made with recycled crushed glass at elevated temperatures

The effect of replacement of fine and coarse aggregates with recycled glass on the fresh and hardened properties of Portland cement concrete at ambient and elevated temperatures is studied. Percentages of replacement of 0–100% of aggregates with fine waste glass (FWG), coarse waste glass (CWG), and fine and coarse waste glass (FCWG) were considered. Soda-lime glass used for bottles was washed and crushed to fine and coarse aggregate sizes for use in the concrete mixes. Samples were cured under 95% RH at room temperatures (20–22 °C), heated in the oven to the desired temperatures, allowed to cool to ambient temperatures, and then tested for their residual compressive strength. The compressive strength of the concrete samples made with waste glass was measured at temperatures up to 700 °C. Moreover, the effect of the percentages of replacement with recycled glass on the slump values and initial and final setting time of concrete has also been measured.     

Using phosphoric acid-impregnated activated carbon to improve the efficiency of chemical filters for the removal of airborne molecular contaminants (AMCs) in the make-up air unit (MAU) of a cleanroom

A coconut shell activated carbon precursor was modified by impregnation with phosphoric acid. The effects of the particle diameter of the impregnated activated carbons (IACs) on the thickness, pressure resistance, and face velocity of a chemical filter were investigated. Furthermore, volatile organic compounds (VOCs) adsorption experiments were carried out to determine the relationship between the removal efficiency and the chemical properties of the adsorbents. The effects of various parameters such as challenge gas concentration, saturated adsorption ratio, impregnation method and impregnant contents were investigated. The results showed that the effect of face velocity on pressure resistance is larger than that of the thickness, that 0.25 M phosphoric acid impregnation of activated carbon can raise VOC removal efficiency by 2–3% (toluene: from 95.8% to 98.1%, isopropanol: from 95.2 to 97.2%), and that the optimal impregnation time is around 1.5 h. A simple shaking impregnation method exhibited better performance than the ultrasonic method.     

Characteristics of particleboard made from recycled wood-waste chips impregnated with phenol formaldehyde resin

The main purpose of this study was to manufacture water-resistant particleboard for use in kitchens and bathrooms, and as flooring-based material and in outdoor environments. The chips were from recycled wood wastes of different wood species. The chips were divided into coarse chips with dimensions of 5–8 mesh and fine chips of 8–20 mesh, then, these chips were immersed in water-soluble phenol formaldehyde (PF) resin solution at concentrations of 4.5%, 6.5% and 10%. After 5 min, they were removed from the PF solution and dried in an oven until in a half-hardened condition. Three-layer mats with target densities of 0.70 and 0.80 g/cm³ were formed by using fine chips for the face layer (25%) and back layer (25%) and coarse chips for the core layer (50%). A conventional hot press was used for fabrication of the particleboard, and the temperature, pressure and pressing time were 453 K, 2.9 MPa, and 5 min, respectively. The nominal dimensions of particleboard were 500×500×12 mm (thick).     

Evaluation of three test methods in determination of formaldehyde emission from particleboard bonded with different mole ratio in the urea–formaldehyde resin

The use of urea–formaldehyde (UF) resins with lower contents of free formaldehyde in the board industry has led to products with very low emissions of formaldehyde. In this study, a detailed account is given of how UF resins with different mole ratios of formaldehyde to urea within the range of 0.97–1.27 influence the formaldehyde emission. In order to evaluate simpler laboratory methods for determining the formaldehyde emission from particleboard, the desiccator (JIS A 5908, 2003) and the EN 120 (European Standard, 1991) have been compared with the 1 m³ chamber method SS 270236 (Swedish Standard of determining formaldehyde emission with chamber test, 1988). Good relationships were obtained between the methods studied with correlation coefficients of >0.9. The value of formaldehyde emission decreased linearly with the mole ratio of formaldehyde to urea down to 1.05 where the effect smoothed out. The effect on the formaldehyde emission of temperature and storage time for tested boards also was studied. The heat treatment lowered the perforator value with resins that had mole ratios equal to or higher than 1.15, at the two lowest mole ratios 0.97 and 1.01, there was a tendency for the heat treatment to increase the perforator value. After the boards were stored for 6 months at 23 °C and 50% RH, the perforator values were unchanged or negligibly changed with the lower mole ratios and there was a more pronounced change with a higher mole ratio of 1.27.     

Milton Keynes Energy Park revisited: Changes in internal temperatures and energy usage

A follow-up study was undertaken of 15 ‘low-energy’ dwellings in Milton Keynes, UK, that were originally monitored for temperature and energy consumption from 1989 to 1991. These measurements were repeated in 2005–2006, with the results compared with the baseline using standardised daily external conditions of 5 °C. The 2005–2006 study found mean temperatures of 19.8 °C (95% confidence interval: 19.7–20.5) for living rooms and 19.3 °C (CI: 19.6–20.1) for main bedrooms. Weak evidence was found for a 10% increase in gas consumption over 15 years to 87 kWh/day (95%CI: 77–96) and overall electricity usage rose by 30% to 15 kWh/day (CI: 13.6–16.5). Dwellings were classified into three groups of low, middle, and high-energy users in 1990. In 2005–2006, this high group consumed more energy than the other two groups combined and accounted for most increases in energy use; their gas usage rose by 20% to 130 kWh/day (110–150), electricity by 75% to 28 kWh/day (CI: 25.3–31.2), and had 50% higher energy intensity at 172 Wh/m² (CI: 150–195). On average the high group comprised dwellings that were larger, had been extended, and whose occupants had higher incomes than the two other groups. The results suggest that research for the development of energy policy, including building regulations, should focus both on how energy is currently used and on households where the largest future increases are likely to occur.     

The effects of paints and moisture content on the indoor air emissions from pinewood (Pinus sylvestris) boards

The emissions of volatile organic compounds (VOCs) from building materials may significantly contribute to indoor air pollution, and VOCs have been associated with odor annoyance and adverse health effects. Wood materials together with coatings are commonly used indoors for furniture and large surfaces such as walls, floors, and ceilings. This leads to high surface-to-volume ratios, and therefore, these materials may participate remarkably to the VOC levels of indoor environment. We studied emissions of VOCs and carbonyl compounds from pinewood (Pinus sylvestris) boards of 10% and 16% moisture contents (MC) with three paints using small-scale test chambers (27 L). The emissions from uncoated pinewood and paints (on a glass substrate) were tested as references. The 28-day experiment showed that the VOC emissions from uncoated pinewood were lower from sample with 16% MC. Painted pinewood samples showed lower emissions compared to paints on glass substrate. Additionally, paints on 16% MC pinewood exhibited lower emissions than on drier 10% MC wood. The emissions from painted pinewood samples were dominated by paint-based compounds, but the share of wood-based compounds increased over time. However, we noticed differences between the paints, and wood-based emissions were clearly higher with the most permeable paint.     

Substrate Effects on VOC Emissions from a Latex Paint

Abstract The effects of two substrates - a stainless steel plate and a gypsum board - on the volatile organic compound (VOC) emissions from a latex paint were evaluated by environmental chamber tests. It was found that the amount of VOCs emitted from the painted stainless steel was 2 to 10 times more than that from the painted gypsum board during the 2-week test period. The dominant chemical species emitted were also different between the two substrates. Data analysis indicated that most VOC emissions from the painted stainless steel occurred in the first 100 h via a fast, evaporation-like process. On the other hand, the majority of the gypsum board VOCs were emitted in a later stage via a slow, diffusion-controlled process. There were measurable emissions of VOCs 11 months after paint application on the gypsum board. It is suggested that, instead of the routinely used substrates such as stainless steel plates, real substrates such as wood or gypsum board should be used for the evaluation of emissions in indoor environments.     

Effect of post-digestion temperature on serial CSTR biogas reactor performance

The effect of post-digestion temperature on a lab-scale serial continuous-flow stirred tank reactor (CSTR) system performance was investigated. The system consisted of a main reactor operated at 55 °C with hydraulic retention time (HRT) of 15 days followed by post-digestion reactors with HRT of 5.3 days. Three post-digestion temperatures (55 °C, 37 °C and 15 °C) were compared in terms of biogas production, process stability, microbial community and methanogenic activity. The results showed that the post-digesters operated at 55 °C, 37 °C and 15 °C gave extra biogas production of 11.7%, 8.4% and 1.2%, respectively. The post-digester operated at 55 °C had the highest biogas production and was the most stable in terms of low VFA concentrations. The specific methanogenic activity tests revealed that the main reactor and the post-digester operated at 55 °C and 37 °C had very active acidogens and methanogens. In contrast, very low methanogenic activity was observed at 15 °C.     

Effects of moisture content on formaldehyde emission and mechanical properties of plywood

Wood is a hygroscopic material and has ability to exchange its moisture content with air. Many mechanical properties are affected by changes in moisture content below the fiber saturation point of wood. This study evaluates the formaldehyde emission and some mechanical properties of poplar and spruce plywood panels manufactured from rotary cut veneers having different moisture content by using urea–formaldehyde (UF) and modified urea formaldehyde by melamine (M+UF). Rotary cut veneers obtained from poplar and spruce logs were classified into three groups and veneers in each group were then conditioned in a climate chamber to either 4–6%, 10–12% or 16–18% moisture content. Plywood panels with three plies and in 6 mm thickness were manufactured for each group. Formaldehyde emission, shear strength, bending strength and modulus of elasticity values of plywood panels were determined. Best bonding results were obtained in plywood panels with veneers having 4–6% moisture content. Lowest mechanical properties were found for plywood panels manufactured from veneers conditioned to 16–18% moisture content. Formaldehyde emission values of poplar and spruce plywood panels decreased with increasing veneer moisture content for both glue types. Formaldehyde emission content of panels decreased with melamine addition into the urea formaldehyde glue mixture.     

Volatile organic compounds from building products—Results from six round robin tests with emission test chambers conducted between 2008 and 2018

Emission testing of volatile organic compounds (VOC) from materials and products is commonly based on emission test chamber measurements. To ensure the comparability of results from different testing laboratories, their measurement performance must be verified. For this purpose, Bundesanstalt für Materialforschung und -prüfung (BAM) organizes an international proficiency test (round robin test, RRT) every two years using well-characterized test materials (one sealant, one furniture board, and four times a lacquer) with defined VOC emissions. The materials fulfilled the requirements of homogeneity, reproducibility, and stability. Altogether, 36 VOCs were included of which 33 gave test chamber air concentrations between 13 and 83 µg/m³. This is the typical concentration range to be expected and to be quantified when performing chamber tests. Three compounds had higher concentrations between 326 and 1105 µg/m³. In this paper, the relative standard deviations (RSD) of BAM round robin tests since 2008 are compared and the improvement of the comparability of the emission chamber testing is shown by the decrease of the mean RSD down to 28% in 2018. In contrast, the first large European interlaboratory comparison in 1999 showed a mean RSD of 51%.     

Estimating the effect of using cool coatings on energy loads and thermal comfort in residential buildings in various climatic conditions

The impact from using cool roof coatings on the cooling and heating loads and the indoor thermal comfort conditions of residential buildings for various climatic conditions is estimated. The energy cooling loads and peak cooling demands are estimated for different values of roof solar reflectance and roof U-value. The results show that increasing the roof solar reflectance reduces cooling loads by 18–93% and peak cooling demand in air-conditioned buildings by 11–27%. The indoor thermal comfort conditions were improved by decreasing the hours of discomfort by 9–100% and the maximum temperatures in non air-conditioned residential buildings by 1.2–3.3 °C. These reductions were found to be more important for poorly or non-insulated buildings. For the locations studied, the heating penalty (0.2–17 kWh/m² year) was less important than the cooling load reduction (9–48 kWh/m² year). The application of cool roof coatings is an effective, minimal cost and easy to use technique that contributes to the energy efficiency and the thermal comfort of buildings.