Gas-phase Semivolatile Organic Compounds Research Articles

Modeling clothing as a secondary source of exposure to SVOCs across indoor microenvironments.

Evidence suggests that clothing can influence human exposure to semi-volatile organic compounds (SVOCs) through transdermal uptake and inhalation. The objectives of this study were [1] to investigate the potential for clothing to function as a transport vector and secondary source of gas-phase SVOCs across indoor microenvironments, [2] to elucidate how clothing storage, wear, and laundering can influence the dynamics of transdermal uptake, and [3] to assess the potential for multiple human occupants to influence the multimedia dynamics of SVOCs indoors. A computational modeling framework (ABICAM) was expanded, applied, and evaluated by simulating and augmenting two "real-world" chamber experiments. A primary strength of this framework was its representation of occupants and their clothing as unique entities with the potential for location changes. Estimates of transdermal uptake of diethyl phthalate (DEP) and di(n-butyl) phthalate (DnBP) were generally consistent with those extrapolated from measured concentrations of urinary metabolites, and those predicted by two other mechanistic models. ABICAM predicted that clean clothing (long sleeves, long pants, and socks, 100% cotton, 1 mm thick) readily accumulated DEP (6900-9700 μg) and DnBP (4500-4800 μg) from the surrounding chamber air over 6 h of exposure to average concentrations of 233 (DEP) and 114 (DnBP) μg·m-3. Because of their high capacity, clean clothing also effectively minimized transdermal uptake. In addition, ABICAM predicted that contaminated clothing functioned as a vector for transporting DEP and DnBP across indoor microenvironments and reemitted 13-80% (DEP) and 3-27% (DnBP) of the accumulated masses over 48 h. Though the estimated secondary inhalation exposures from contaminated clothing were low compared to the corresponding primary exposures, these secondary exposures could be accentuated in other contexts, for example, involving longer timeframes of clothing storage, multiple occupants wearing contaminated clothing, and/or repeated instances of clothing-mediated transport of contaminants (e.g., from an occupational setting). This modeling study reaffirms the effectiveness of clean clothing in reducing transdermal uptake of airborne SVOCs and conversely, that contaminated clothing could be a source of SVOC exposure via transdermal uptake and by acting as a vector for transporting those contaminants to other locations.

Field Calibration and PAS-SIM Model Evaluation of the XAD-Based Passive Air Sampler for Semi-Volatile Organic Compounds.

The use of passive air samplers (PAS) for semi-volatile organic compounds (SVOCs) continues to expand. To advance quantitative understanding of uptake kinetics, we calibrated the XAD-PAS, using a styrene-divinylbenzene sorbent, through a year-long side-by-side deployment with an active sampler. Twelve XAD-PASs, deployed in June 2020, were retrieved at 4-week intervals, while gas phase SVOCs were quantified in 48 consecutive week-long active samples taken from June 2020 to May 2021. Consistent with XAD's high uptake capacity, even relatively volatile SVOCs, such as hexachlorobutadiene, displayed linear uptake throughout the entire deployment. Sampling rates (SRs) range between 0.1 and 0.6 m3 day-1 for 26 SVOCs, including brominated flame retardants, organophosphate esters, and halogenated methoxylated benzenes. SRs are compared with experimental SRs reported previously. The ability of the existing mechanistic uptake model PAS-SIM to reproduce the observed uptake and SRs was evaluated. Agreement between simulated and measured uptake curves was reasonable but varied with compound volatility and the assumed stagnant air layer boundary thickness. Even though PAS-SIM succeeds in predicting the SR range for the studied SVOCs, it fails to capture the volatility dependence of the SR by underestimating the length of the linear uptake period and by failing to consider the kinetics of sorption.

Gas-Particle Partitioning of Semivolatile Organic Compounds in a Residence: Influence of Particles from Candles, Cooking, and Outdoors.

Semivolatile organic compounds (SVOCs) represent an important class of indoor pollutants. The partitioning of SVOCs between airborne particles and the adjacent air influences human exposure and uptake. Presently, little direct experimental evidence exists about the influence of indoor particle pollution on the gas-particle phase partitioning of indoor SVOCs. In this study, we present time-resolved gas- and particle-phase distribution data for indoor SVOCs in a normally occupied residence using semivolatile thermal desorption aerosol gas chromatography. Although SVOCs in indoor air are found mostly in the gas phase, we show that indoor particles from cooking, candle use, and outdoor particle infiltration strongly affect the gas-particle phase distribution of specific indoor SVOCs. From gas- and particle-phase measurements of SVOCs spanning a range of chemical functionalities (alkanes, alcohols, alkanoic acids, and phthalates) and volatilities (vapor pressures from 10-13 to 10-4 atm), we find that the chemical composition of the airborne particles influences the partitioning of individual SVOC species. During candle burning, the enhanced partitioning of gas-phase SVOCs to indoor particles not only affects the particle composition but also enhances surface off-gassing, thereby increasing the total airborne concentration of specific SVOCs, including diethylhexyl phthalate.

Measurement methods and impact factors for the key parameters of VOC/SVOC emissions from materials in indoor and vehicular environments: A review.

The emissions of volatile organic compounds (VOCs) and semi-volatile organic compounds (SVOCs) from indoor building and vehicle cabin materials can adversely affect human health. Many mechanistic models to predict the VOC/SVOC emission characteristics have been proposed. Nowadays, the main obstacle to accurate model prediction is the availability and reliability of the physical parameters used in the model, such as the initial emittable concentration, the diffusion coefficient, the partition coefficient, and the gas-phase SVOC concentration adjacent to the material surface. The purpose of this work is to review the existing methods for measuring the key parameters of VOCs/SVOCs from materials in both indoor and vehicular environments. The pros and cons of these methods are analyzed, and the available datasets found in the literature are summarized. Some methods can determine one single key parameter, while other methods can determine two or three key parameters simultaneously. The impacts of multiple factors (temperature, relative humidity, loading ratio, and air change rate) on VOC/SVOC emission behaviors are discussed. The existing measurement methods span very large spatial and time scales: the spatial scale varies from micro to macro dimensions; and the time scale in chamber tests varies from several hours to one month for VOCs, and may even span years for SVOCs. Based on the key parameters, a pre-assessment approach for indoor and vehicular air quality is introduced in this review. The approach uses the key parameters for different material combinations to pre-assess the VOC/SVOC concentrations or human exposure levels during the design stage of buildings or vehicles, which can assist designers to select appropriate materials and achieve effective source control.

Impacts of sampling-tube loss on quantitative analysis of gaseous semi-volatile organic compounds (SVOCs) using an SPME-based active sampler.

Active samplers are widely used in the quantification of gaseous semi-volatile organic compounds (SVOCs). A sampling tube is often assembled upstream of the sampler, especially in the active samplers used for separating the particle-phase and gas-phase SVOCs and in the newly-designed active sampler based on solid-phase microextraction (SPME). However, gaseous SVOCs can be easily adsorbed by the sampling tube, which may induce significant errors to the quantitative results. Taking the SPME-based active sampler as an example, a mass-transfer model was developed to characterize the sampling-tube loss of gaseous SVOCs. Experiments involving six SVOCs were conducted. The model predictions (with a best-fit surface/air partition coefficient of SVOCs) were found to be consistent with the measurements. Both model predictions and experimental data indicated that the measured concentrations were significantly lower than the actual concentration (around 60% lower) due to the sampling-tube loss. The duration of sampling-tube loss (τe, minutes to days) varied with the volatility of SVOCs (vapor pressure, Vp), i.e., log τe linearly increased as increasing log Vp. The relationship could be helpful for determining the sampling strategies to eliminate (reduce) the effects of sampling-tube loss according to the volatility of SVOCs. The above conclusions may be also applicable for other active samplers of gaseous SVOCs. However, further studies are required to quantify the effects of sampling-tube loss for other active samplers due to the difference in the size and shape of the sampling tube between them and the SPME-based active sampler. The corresponding mass-transfer model and experimental procedure may require adjustment as appropriate.

Field comparison of passive polyurethane foam and active air sampling techniques for analysis of gas-phase semi-volatile organic compounds at a remote high-mountain site

Polyurethane foam passive air samplers (PUF-PAS) are good candidates for the determination of gas-phase semi-volatile organic compound (SVOC) air concentrations in high-mountain areas over long periods because they do not require an energy supply. However, the harsh meteorological conditions present in such locations can increase the uncertainties inherently associated to PAS sampling rates due to the many variables involved in their calculation and to the assumptions made regarding PUF diffusive uptake mechanics, which can considerably bias the resulting concentrations. Therefore, we studied the performance of PUF-PASs in a remote location in the Pyrenees mountain range for the analysis of several SVOCs in air, including polychlorobiphenyls (PCBs), hexachlorobenzene, pentachlorobenzene, polycyclic aromatic hydrocarbons (PAHs), and the less studied emerging organophosphate flame retardants (OPFRs). An in-situ PUF-PAS calibration using Performance Reference Compounds (PRCs) provided compound- and sampler-specific sampling rates, showing mean experimental errors (12%) that adequately conformed to an estimate of their expanded theoretical uncertainties (15%). This showcases the suitability of this calibration strategy in an area with conditions beyond those typically considered in calibration efforts available to date. Moreover, gas-phase concentrations of the studied pollutants from PUF-PAS samples showed very good agreement (R2 up to 0.91, p < 0.01) when compared to those obtained using a conventional high-volume active air sampler (PUF-AAS), with some minor deviations observed for PAHs caused by the seasonality in their atmospheric concentrations. No relevant levels of pollutants preferentially bound to the particle phase were detected in the PUF-PASs, the particle infiltration efficiency of the sampler configuration used was found to be low, and compounds typically distributed between the gas and particle phases of AAS samples revealed profiles consistent with their vapor pressures, except for some OPFRs.

Characterization of phthalates in sink and source materials: Measurement methods and the impact on exposure assessment

The fate and transport of semi-volatile organic compounds (SVOCs) in residential environments is significantly influenced by emission and sorption processes, which can be characterized by three key parameters: the gas-phase SVOC concentration adjacent to the material surface (y0); the diffusion coefficient (Dm); and the partition coefficient (K). Accurate determination of these three key parameters is critical for investigating SVOC mass transfer principles, and for assessing human health risks. Based on the mass transfer process of phthalates in a ventilated chamber, a novel method is developed to simultaneously measure Dm and K (key sorption parameters) in sink materials. The Dm and K of four target phthalates in a common T-shirt (sink material) are determined, and compared with those reported in literature. Results demonstrate that the measured parameters are in good agreement with those previously reported (relative deviation < 20 %), validating the effectiveness of proposed method. In addition, this method can be applied to determine y0, a key parameter from source materials. Results indicate that y0 determined with this method is consistent with that measured by literature method. Finally, dermal exposure analysis is performed, showing that dermal uptake of target phthalates is greatly affected by clothes.

A needle trap device method for sampling and analysis of semi-volatile organic compounds in air

Semi-volatile organic compounds (SVOCs), such as phthalates, organophosphates, and polybrominated diphenyl ethers, are emerging as an important class of pollutants that are of serious health concerns. Determining concentrations of these pollutants is of great importance for environmental and exposure studies. In this work, a needle trap device (NTD) method was developed to measure the concentration of SVOCs in air samples. Sorbents were packed in the NTD to capture SVOCs with the aid of a sampling pump. NTD operational parameters, such as desorption temperature, desorption time, and sampling flow rate, were optimized for the target SVOCs. The limit of detection for air sampling by the NTD method ranged between 5 pg and 1 ng, depending on the SVOC compound. The variations in terms of NTD repeatability and reproducibility were lower than 14% for all cases. In addition, the influence of other experimental parameters, such as sampling temperature and humidity, breakthrough volume, NTD storage time, as well as carryover effect were examined. Finally, NTDs were used to determine emissions of gas-phase SVOCs from various consumer products in an emission cell and to collect total airborne SVOC samples (gas and particle phases) in an office. The results of NTD method were in an agreement with data obtained by conventional active sampling methods using Tenax® sorbent tubes and polyurethane foam samplers, but with improvements of relative standard deviation, sensitivity, and sampling time. The results demonstrated that the NTD method is a simple, sensitive, effective, reusable, and inexpensive technique for sampling and analyzing SVOCs in the concentration range from 2 ng m−3 to 100 μg m−3 in air.

Dynamic method to measure partition coefficient and mass accommodation coefficient for gas‒particle interaction of phthalates

The particle-gas partition coefficient (Kp) and mass accommodation coefficient (α) are two parameters characterizing the gas-particle interaction of semi-volatile organic compounds (SVOCs). Most of the available methods for measuring Kp require equilibrium at the chamber outlet, implying substantial preliminary testing. The need to separate gas-phase and particle-phase SVOCs also reduces the method accuracy. Few studies measuring α for indoor-related SVOCs are available, and they usually ignore the wall loss of SVOCs, resulting in reduced measurement accuracy. To overcome these deficiencies, we developed a dynamic method coupling a laminar flow tube chamber and an SVOC mass transfer model. Using the interaction between gas-phase di-2-ethylhexyl phthalate (DEHP) and (NH4)2SO4 particles (with diameters in the range of 10–600 nm) as an example, experiments were performed to evaluate the effectiveness and accuracy of the dynamic method. For the experimental conditions investigated (temperature = 25 °C and relative humidity <10%), gas-particle interaction between DEHP and (NH4)2SO4 particles is governed by surface adsorption because (NH4)2SO4 particles are in solid state. In this case, gas-particle partitioning should be characterized by the surface-area-normalized partition coefficient (KpA). KpA and α were measured to be 260 ± 80 m and 0.20 ± 0.05, respectively. Both are consistent with results reported in the literature. The method applicability for other SVOC-particle combinations and the improvement of method accuracy require further study.Copyright © 2019 American Association for Aerosol Research

Lattice Boltzmann method simulation of SVOC mass transfer with particle suspensions

Semi-volatile organic compounds (SVOC) exist in indoor air at very low concentrations (usually less than 100 µg/m3), but do great harm to human health. SVOC pollutants transfer in indoor air with suspended particles so complicatedly that traditional experimental methods are hardly to reveal the mass-transfer mechanism. This study employs Lattice Boltzmann method (LBM) to investigate the mass transfer behaviours of two-phase SVOC pollutants (gas- and particle-phase), and compare two widely-used gas/particle partition models (the instantaneous equilibrium model and the dynamic model). LBM is used to simulate the fluid flows and SVOC mass transfer, and the cell automation (CA) probabilistic model is applied to simulate the particle transport. The interaction between the gas- and particle-phase of SVOC is considered in the source term of the Lattice Boltzmann equations. One particle is firstly simulated in order to focus on the particle-phase concentration, then a large number of particles are simulated to focus on the effect of particles on the concentration field of SVOC. The simulation results show: (i) particles in the instantaneous equilibrium model for gas/particle partition always help gas-phase SVOC transport in indoor air by particle-mediation effect, while such an effect in the dynamic model is greatly determined by Kp and residence time of particles; (ii) particle-mediation effect can also increase the emission rate, and a non-uniform distribution of particles predicted by our numerical model indicates that such an additional emission rate increases exponentially with particle concentration, because a small number of particles have little possibility of approaching emission surface. (iii) Our numerical model can effectively estimate SVOC concentration in the presence of airborne particles by tracking each particle. These results highlight the roles of airborne particles in the transport of indoor SVOC pollutants, and are expected to be useful to consider dust deposition and resuspension when particles are in a realistic size distribution.

Modeling the formation and growth of organic films on indoor surfaces.

Emission, transport, and fate of semi-volatile organic compounds (SVOCs), which include plasticizers, flame retardants, pesticides, biocides, and oxidation products of volatile organic compounds, are influenced in part by their tendency to sorb to indoor surfaces. A thin organic film enhances this effect, because it acts as both an SVOC sink and a source, thus potentially prolonging human exposure. Unfortunately, our ability to describe the initial formation and subsequent growth of organic films on indoor surfaces is limited. To overcome this gap, we propose a mass transfer model accounting for adsorption, condensation, and absorption of multiple gas-phase SVOCs on impervious, vertical indoor surfaces. Further model development and experimental research are needed including more realistic scenarios accounting for surface heterogeneity, non-ideal organic mixtures, and particle deposition.

Predicting Dermal Exposure to Gas-Phase Semivolatile Organic Compounds (SVOCs): A Further Study of SVOC Mass Transfer between Clothing and Skin Surface Lipids.

Dermal exposure to indoor gas-phase semivolatile organic compounds (SVOCs) has recently received a great deal of attention, and this has included evaluating the role of clothing in this process. Several models have been developed to assess dermal exposure to SVOCs, based on the transient mass transfer of SVOCs from air to dermal capillaries. Assumptions of these models are either that clothing completely retards SVOC transport, or that there is an air gap of constant thickness between the clothing and the surface of the skin, which may lead to errors in the model calculations. To solve this problem, we tried to describe SVOC transport between clothing and epidermis by considering two parallel processes: partitioning of SVOCs by direct contact (ignored in existing models), and Fickian diffusion through the air gap. Predictions from the present model agree well with the experimental data found in the literature (dermal uptake of diethyl phthalate (DEP) and di- n-butyl phthalate (DnBP) of a clothed participant). This study provides a useful tool to accurately assess dermal exposure to indoor SVOCs, especially for evaluating the effects of clothing on dermal exposure.

Time dependence of characteristic parameter for semi-volatile organic compounds (SVOCs) emitted from indoor materials

Semi-volatile organic compounds (SVOCs) are widely used in various indoor materials and their adverse health effects have been increasingly recognized. The gas-phase SVOC concentration in equilibrium with the source material (y0), as a characteristic parameter for SVOC sources, is mostly assumed to be constant in previous studies. However, decreases in y0 with time have been observed in some studies. As a first step to reveal the mechanism behind the phenomenon, this study quantitatively investigated the variation of y0 over time under two conditions: natural exposure to outdoor ambient (Case 1), and storage in a controlled ventilated chamber (Case 2). Three phthalates (Di-iso-butyl Phthalate (DiBP), Di-n-butyl Phthalate (DnBP), and di-(2-ethylhexyl) phthalate (DEHP)) emitted from polyvinyl chloride (PVC) floorings and one flame retardant (tris(2-chloroisopropyl) phosphate, TCPP) emitted from polyurethane foam (PUF) were targeted. Experimental results indicated that, for SVOCs with higher volatility, i.e., DiBP, DnBP, and TCPP, y0 decreased 16%–49% after 60 days' exposure for Case 1; and 16%–36% for Case 2. For SVOCs with lower volatility, i.e., DEHP, no significant decrease in y0 was observed after 60 days in both cases; while if prolonging the time to about 1.5 years, a decrease of 38% was observed. Discussion about potential reasons for the decrease of y0 was presented. The results obtained here provide a further understanding about SVOC source characteristics and therefore help providing source strength for estimating indoor SVOC health exposure.

SPME-Based Ca-History Method for Measuring SVOC Diffusion Coefficients in Clothing Material.

Clothes play an important role in dermal exposure to indoor semivolatile organic compounds (SVOCs). The diffusion coefficient of SVOCs in clothing material (Dm) is essential for estimating SVOC sorption by clothing material and subsequent dermal exposure to SVOCs. However, few studies have reported the measured Dm for clothing materials. In this paper, we present the solid-phase microextraction (SPME) based Ca-history method. To the best of our knowledge, this is the first try to measure Dm with known relative standard deviation (RSD). A thin sealed chamber is formed by a circular ring and two pieces of flat SVOC source materials that are tightly covered by the targeted clothing materials. Dm is obtained by applying an SVOC mass transfer model in the chamber to the history of gas-phase SVOC concentrations (Ca) in the chamber measured by SPME. Dm's of three SVOCs, di-iso-butyl phthalate (DiBP), di-n-butyl phthalate (DnBP), and tris(1-chloro-2-propyl) phosphate (TCPP), in a cotton T-shirt can be obtained within 16 days, with RSD less than 3%. This study should prove useful for measuring SVOC Dm in various sink materials. Further studies are expected to facilitate application of this method and investigate the effects of temperature, relative humidity, and clothing material on Dm.

Influence of airborne particles on convective mass transfer of SVOCs on flat surfaces: Novel insight and estimation formula

Impact of airborne particles on convective mass transfer coefficient (hm) of semivolatile organic compounds (SVOCs) at flat surfaces has been investigated by assuming gas-particle equilibrium partition. In realistic indoor environments, however, this equilibrium partition might not be attained because the time required to reach equilibrium could be longer than residence time of airborne particles. No quantitative result of influence of particles on hm under a non-equilibrium state has been given yet. A mass transfer model was used in this study to quantify this influence for the laminar air flow. The influence, calculated as ratio of hm with particles present to hm with particles absent, ε, was found to significantly depend on three dimensionless parameters: Bip, R, and Cp∗(∞). Bip represents the ratio of mass transfer rate between gas- and particle-phases SVOCs to mass transfer rate of gas-phase SVOCs transporting across the concentration boundary layer, R is the ratio of SVOC mass in particle-phase to that in gas-phase at equilibrium state, and Cp∗(∞) characterizes non-equilibrium degree of particle-phase SVOCs in the bulk air (higher non-equilibrium degree as it deviates further away from one, as one corresponds to equilibrium). At equilibrium state (Cp∗(∞)=1), the presence of particles enhances hm (ε>1) to the same extent for source surfaces and sink ones. At non-equilibrium state, ε varies linearly as Cp∗(∞) changes (Cp∗(∞)>1 for source surface, and Cp∗(∞)<1 for sink surface). The presence of particles always enhances hm for SVOC source surfaces. In contrast, it can either enhance (ε>1) or weaken (0<ε<1) hm for sink surfaces, depending on non-equilibrium degree between gas-phase SVOCs and particles (characterized by Cp∗(∞)). An empirical formula relating ε with these three parameters was obtained. Good agreement between predictions by the formula and experimental results in the literature moderately supported its reliability. Results of this study could be useful in better estimating indoor SVOC concentrations, as well as assessing and controlling human exposure to indoor SVOCs.

Artefacts in semivolatile organic compound sampling with polyurethane foam substrates in high volume cascade impactors

ABSTRACTPolyurethane foam (PUF) is known to sorb gas-phase semivolatile organic compounds (SVOCs) from ambient air and is used routinely in conventional high volume filter-sorbent sampling of such pollutants. PUF rings have also been employed as impaction substrates in a high volume cascade impactor (HVCI) used as a sampler for the evaluation of particle toxicity. Though nonvolatile particles (e.g., trace metals, inorganic ions) have been the primary focus, the sampler has also been used to measure particulate SVOC concentrations in ambient air. The aim of this work is to investigate the validity of the latter approach. The results of three sets of experiments conducted in Canada and Denmark are reported herein. Model compounds included native and deuterated polycyclic aromatic hydrocarbons (PAHs). The experiments demonstrated that HVCI PUF substrates sorb gas-phase PAH compounds and that the sorbed mass is subject to mobilization through and out of the sampler. Particulate concentrations of low molecular...

Source-apportioned PM2.5 incorporating gas-phase partitioned semi-volatile organic compounds and hospitalizations in Denver

Introduction: Identifying emission sources underlying associations between PM2.5 and adverse health effects is important for guiding air quality management decisions. The Denver Aerosol Sources and Health study aimed to improve PM2.5 source apportionment by including semi-volatile organic compounds (SVOC). Associations between sources and daily hospitalizations were compared using source estimates from PM2.5 components including measured particle-phase SVOC only and estimated total SVOC. Methods: Daily concentrations of PM2.5 mass, metals, ions, elemental carbon, and speciated organic compounds were measured in Denver, CO in 2003-2005. Gas-phase SVOC were estimated using gas-particle partitioning theory to obtain total SVOC. Two sets of PM2.5 chemical source groups were estimated using positive matrix factorization for particle-phase and total SVOC. Six source groups were identified for each: inorganic ions, n-alkanes, steranes, light SVOC, polycyclic aromatic hydrocarbons, and bulk carbon. Daily counts of cardiovascular and respiratory hospitalizations were obtained for the 5-county Denver area. Using generalized additive models, relative risks (RR) of hospitalizations were estimated for total and particle SVOC based sources for day lags 0 to 14, adjusting for meteorology, day of week and long-term trends. Constrained distributed lag models were used to assess lag patterns of RRs. Results: RRs and lag patterns of cardiovascular hospitalization differed for light SVOC and bulk carbon source groups when using particle-phase or total SVOC-based source estimates, but were similar for other source groups. Lag patterns for respiratory hospitalization RRs were generally similar, but some RRs differed, such as those at early lags for light SVOC and bulk carbon source groups. Conclusions: PM2.5 source apportionment using speciated data incorporating total SVOC may better characterize PM2.5 sources and improve identification of health impacts from specific sources.

Effect of measurement protocol on organic aerosol measurements of exhaust emissions from gasoline and diesel vehicles

Exhaust emissions of semi-volatile organic compounds (SVOC) from passenger vehicles are usually estimated only for the particle phase via the total particulate matter measurements. However, they also need to be estimated for the gas phase, as they are semi-volatile. To better estimate SVOC emission factors of passenger vehicles, a measurement campaign using a chassis dynamometer was conducted with different instruments: (1) a constant volume sampling (CVS) system in which emissions were diluted with filtered air and sampling was performed on filters and polyurethane foams (PUF) and (2) a Dekati Fine Particle Sampler (FPS) in which emissions were diluted with purified air and sampled with on-line instruments (PTR-ToF-MS, HR-ToF-AMS, MAAP, CPC). Significant differences in the concentrations of organic carbon (OC) measured by the instruments are observed. The differences can be explained by sampling artefacts, differences between (1) the time elapsed during sampling (in the case of filter and PUF sampling) and (2) the time elapsed from emission to measurement (in the case of on-line instruments), which vary from a few seconds to 15 min, and by the different dilution factors. To relate elapsed times and measured concentrations of OC, the condensation of SVOC between the gas and particle phases is simulated with a dynamic aerosol model. The simulation results allow us to understand the relation between elapsed times and concentrations in the gas and particle phases. They indicate that the characteristic times to reach thermodynamic equilibrium between gas and particle phases may be as long as 8 min. Therefore, if the elapsed time is less than this characteristic time to reach equilibrium, gas-phase SVOC are not at equilibrium with the particle phase and a larger fraction of emitted SVOC will be in the gas phase than estimated by equilibrium theory, leading to an underestimation of emitted OC if only the particle phase is considered or if the gas-phase SVOC are estimated by equilibrium theory. Current European emission inventories for passenger cars do not yet estimate gas-phase SVOC emissions, although they may represent 60% of total emitted SVOC (gas + particle phases).

Temperature dependence of the particle/gas partition coefficient: An application to predict indoor gas-phase concentrations of semi-volatile organic compounds

The indoor gas-phase concentrations of semi-volatile organic compounds (SVOCs) can be predicted from their respective concentrations in airborne particles by applying the particle/gas partitioning equilibrium. The temperature used for partitioning is often set to 25°C. However, indoor temperatures frequently differ from this reference value. This assumption may result in errors in the predicted equilibrium gas-phase SVOC concentrations. To improve the prediction model, the temperature dependence of the particle/gas partition coefficient must be addressed. In this paper, a theoretical relationship between the particle/gas partition coefficient and temperature was developed based on the SVOC absorptive mechanism. The SVOC particle/gas partition coefficients predicted by employing the derived theoretical relationship agree well with the experimental data retrieved from the literature (R>0.93). The influence of temperature on the equilibrium gas-phase SVOC concentration was quantified by a dimensionless analysis of the derived relationship between the SVOC particle/gas partition coefficient and temperature. The predicted equilibrium gas-phase SVOC concentration decreased by between 31% and 53% when the temperature was lowered by 6°C, while it increased by up to 750% when the indoor temperature increased from 15°C to 30°C.

A simple method to measure the gas-phase SVOC concentration adjacent to a material surface.

Assessing human exposure to semivolatile organic compounds (SVOCs) emitted from materials and products is difficult because methods are not available to easily measure the key emission parameters. A simple method based on a passive sampling technique was thus developed to measure the gas-phase SVOC concentration (y0 ) immediately adjacent to the material surface in a consumer product. The method employs standard stainless steel thermal desorption tubes, with values of y0 and an additional unknown parameter, K, the tube surface/air partition coefficient inside the desorption tube, obtained by fitting a diffusion model to the sampling data. Phthalates in two types of polyvinyl chloride flooring were selected to test the method. The values of y0 and K agree well with those measured in independent chamber tests. The y0 measurement method is shown to be applicable to chemicals with a wide range of vapor pressures. This novel method should be useful for assessing potential exposure to SVOCs in consumer products as well as for exposure-based prioritization of chemicals and their associated products in indoor environments.