Particle-phase Semi-volatile Organic Compounds Research Articles

Modeling the bioaccessibility of inhaled semivolatile organic compounds in the human respiratory tract.

The bioaccessibility of semivolatile organic compounds (SVOCs) via inhalation has rarely been studied, as indicated by the literature. There is no model to calculate the SVOC bioaccessibility following inhalation, and measurement data have focused on only a few polycyclic aromatic hydrocarbons (PAHs) in the particle phase. The present work developed a mechanistic model to address the mass transfer of inhaled SVOCs among the gas, particle and mucus phases in the human respiratory tract. The model considers (1) the SVOC partitioning between the gas and particle phases as well as between the gas and mucus phases and (2) the deposition of gas- and particle-phase SVOCs in the mucus of the respiratory tract. Based on the model, the inhalation bioaccessibility for 72 SVOCs was calculated. The SVOCs were measured in French dwellings at the nationwide scale, and their median concentrations in both the gas and particle phases were used for the bioaccessibility calculations. The results show that the inhalation bioaccessibility varies considerably from one compound to another, e.g., between 0.62 and 1.00 for phthalates, between 0.71 and 0.79 for polybrominated diphenyl ethers (PBDEs), between 0.48 and 0.56 for polychlorinated biphenyls (PCBs), between 0.48 and 1.00 for different chemical families of pesticides and between 0.48 and 0.90 for PAHs.

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

Design and application of a novel integrated microsampling system for simultaneous collection of gas- and particle-phase semivolatile organic compounds

An integrated microsampling approach based on active microextraction was developed to study semivolatile organic compounds (SVOCs). This microsampling system included an in-tube hollow-fiber solid-phase microextraction device in combination with a sorbent tube that can be applied in parallel to collect gas- and particle-phase SVOCs. The preparation procedure, theory, and application of two devices were characterized and validated by the single fiber theory and scanning mobility particle sizer experiments. The influence of the optimization parameters (sampling time, flow rate, and breakthrough volume) on the extraction process was studied in detail. The performance of the system was tested via simultaneous collection of a range of gas and particle samples of ethylbenzene, xylenes, n-alkanes, polycyclic aromatic hydrocarbons, and monoterpenes. The collection efficiencies of the two devices were more than 90% for most target compounds. Typically, relative standard deviation values in the range 2–6% were obtained, depending on the compound. The calibration curves for each compound were reproducible and linear over the concentration ranges normally found in atmospheric samples. Both devices were used to collect ambient air samples during a haze period and performed well in the extraction of both gas- and particle-phase SVOCs at the ng m−3 levels. The results from phase studies were used for further evaluation of the gas/particle partitioning of SVOCs. Application of this integrated microsampling system in the field validated its use as a simple, rapid, reusable, and cost-effective screening tool.

Characterizing particle resuspension from mattresses: chamber study.

People spend approximately one-third of their lives sleeping, where they can be exposed to a myriad of particle-bound biological agents and chemical pollutants that originate within mattresses and bedding, including allergens, fungal spores, bacteria, and particle-phase semi-volatile organic compounds. Full-scale particle resuspension experiments were conducted in an environmental chamber, where volunteers performed a prescribed movement routine on an artificially seeded mattress. Human movements in bed, such as rolling from the prone to supine position, were found to resuspend settled particles, leading to elevations in airborne particle concentrations. Resuspension rates were estimated for the size fractions of 1-2 μm, 2-3 μm, 3-5 μm, 5-10 μm, and 10-20 μm, and were in the range of 10(-3) to 10(1) h(-1). Particle size had the most significant impact on the resuspension rate, whereas dust loading, volunteer body mass, and ventilation rate had a much smaller impact. Resuspension increased with the intensity of a movement, as characterized by surface vibrations, and decreased with repeated movement routines. Inhalation exposure was characterized with the intake fraction metric. Intake fractions increased as the particle size and ventilation rate decreased and ranged from 10(2) to 10(4) inhaled particles per million resuspended, demonstrating that a significant fraction of released particles can be inhaled by sleeping occupants. Full-scale chamber experiments with human volunteers demonstrate that body movements in bed can resuspend settled particles from mattresses, leading to elevated airborne particle concentrations in both the breathing zone and bulk air of the chamber. Numerous variables influence resuspension, including particle size and intensity of a specific body movement. The results suggest that human-induced resuspension in the sleep microenvironment may play an important role in contributing to our inhalation exposure to mattress dust pollutants.

Carbonaceous Aerosols Emitted from Light-Duty Vehicles Operating on Gasoline and Ethanol Fuel Blends

This study examines the chemical properties of carbonaceous aerosols emitted from three light-duty gasoline vehicles (LDVs) operating on gasoline (e0) and ethanol-gasoline fuel blends (e10 and e85). Vehicle road load simulations were performed on a chassis dynamometer using the three-phase LA-92 unified driving cycle (UDC). Effects of LDV operating conditions and ambient temperature (-7 and 24 °C) on particle-phase semivolatile organic compounds (SVOCs) and organic and elemental carbon (OC and EC) emissions were investigated. SVOC concentrations and OC and EC fractions were determined with thermal extraction-gas chromatography-mass spectrometry (TE-GC-MS) and thermal-optical analysis (TOA), respectively. LDV aerosol emissions were predominantly carbonaceous, and EC/PM (w/w) decreased linearly with increasing fuel ethanol content. TE-GC-MS analysis accounted for up to 4% of the fine particle (PM2.5) mass, showing the UDC phase-integrated sum of identified SVOC emissions ranging from 0.703 μg km(-1) to 18.8 μg km(-1). Generally, higher SVOC emissions were associated with low temperature (-7 °C) and engine ignition; mixed regression models suggest these emissions rate differences are significant. Use of e85 significantly reduced the emissions of lower molecular weight PAH. However, a reduction in higher molecular weight PAH entities in PM was not observed. Individual SVOC emissions from the Tier 2 LDVs and fuel technologies tested are substantially lower and distributed differently than those values populating the United States emissions inventories currently. Hence, this study is likely to influence future apportionment, climate, and air quality model predictions that rely on source combustion measurements of SVOCs in PM.

Daily mortality and PM2.5 sources in Denver estimated using only particle-phase or total semi-volatile organic compounds (SVOCs)

Background: Source apportionment approaches have provided insights into chemical classes of fine particle matter (PM2.5) responsible for adverse health effects. The Denver Aerosol Sources and Health (DASH) study used the Positive Matrix Factorization (PMF) to identify chemical classes of PM2.5 in the Denver area. Aim: To compare estimated health effects of PM2.5 components with those of chemical classes identified by PMF based on particle-phase or total semi-volatile organic compounds (SVOCs). Methods: Daily measurements of four PM2.5 chemical components (elemental and organic carbon (EC and OC), sulfate, and nitrate), as well as a large number of organic compounds, were obtained over a 32 month period at a single monitoring station located in populated residential area in Denver. PMF factors were estimated based on particle-phase SVOCs only and total SVOCs adding estimated gas-phase SVOCs. The two approaches resulted in eight (Inorganic Ion, n alkane, summer odd n alkane, light n alkane polycyclic aromatic hydrocarbon (PAH), medium alkane alkanoic acid, PAH, winter methoxyphenol, and EC sterane) and seven (n alkane, light SVOC, PAH, summer ECOC, EC sterane, sulfate, and nitrate) factors, respectively. Daily death counts of cardiovascular and respiratory diseases were obtained from the Denver death certificate records. We used generalized additive models to estimate relative risks of mortality at lags 0 to 3 for each of PM2.5 components and PMF factors adjusting for daily humidity and temperature, long-term temporal trend, and day of week. Results: None of four PM2.5 components was associated with daily mortality. With the total SVOC source factors, the PAH factor was associated with cardiovascular mortality at lag 0; with both PMF approaches, n alkanes were associated with respiratory mortality at lag 3. Conclusions: Use of source apportionment allowed us to identify PM2.5 mortality associations that were not found using only single PM2.5 components.

Evaluation of an annular denuder tubes for atmospheric PAH partitioning studies—1: evaluation of the trapping efficiency of gaseous PAHS

This paper is an evaluation of the gas phase collection efficiency of a commercially available annular denuder sampler used to collect gas and particle phase semivolatile organic compounds. Laboratory and field experiments were carried out to determine the gas phase collection efficiency using naphthalene as reference compound. Laboratory tests were performed to study the influence of environmental conditions (temperature, relative humidity and gas phase concentration) and sampling conditions (sampling flow rate, and sampling duration) on the collection efficiency. During laboratory experiments, the collection efficiency of the gas phase was measured using a dynamic gas generator. It was above 90% for a range of experimental conditions covering: temperature from 9°C to 39°C, relative humidity from 30% to 90%, sampling duration up to 14 h, flow rate of 1 and 2 m3 h−1 and quantity of gaseous naphthalene considerably higher than the one usually collected during atmospheric sampling.

Application of the multimedia urban model to compare the fate of SOCs in an urban and forested watershed.

A multimedia model has been developed to estimate the dynamics of semivolatile organic compounds (SOCs) in urban areas. The model is based on a Level III fugacity model of Mackay and consists of six compartments: air, surface water, sediment, soil, vegetation, and an organic film that coats impervious surfaces. The model was used to illustrate the effect of impervious surfaces in urban areas by parametrization for downtown, Toronto, Canada, and modification of the same area to simulate forested conditions. With illustrative emissions of PCB homologues to air, the model indicates that most chemicals are lost by advection, with the remainder undergoing air-to-surface (organic film or vegetation) transfer. Under urban conditions chemicals with Log[K(OA)] < 7.5 volatilize from the film into air where they are susceptible to advection and photolytic degradation. Chemicals with Log[K(OA)] > 7.5 are washed off the film to surface waters where they may undergo volatilization, advection, sedimentation, and degradation. Both loss mechanisms from the film increase the overall mobility of SOCs in the urban relative to the forested environment. In forested areas, vegetation more efficiently accumulates gas- and particle-phase SOCs and subsequently transfers them to surface soils, the greatest chemical reservoir, where they are relatively immobile.

Developing a multimedia model of chemical dynamics in an urban area

A multimedia model has been developed to account for the movement of semi-volatile organic compounds (SOCs) in an urban environment. The model, based on a Level III fugacity model of D. Mackay (Multimedia Environmental Models: The Fugacity Approach, Lewis Publishers, Boca Raton, FL, 1991), consists of six compartments: air, surface water, sediment, soil, vegetation, and an organic film that coats impervious surfaces. The latter is a newly identified compartment into which gas-phase SOCs partition and particle-phase SOCs are believed to be efficiently captured (M.L. Diamond, S.E. Gingrich, K. Fertuck, B.E. McCarry, G.A. Stern, B. Billeck, B. Grift, D. Brooker, T.D. Yager, Environ. Sci. Technol., 34 (2000a), 2900–2908). The model, parameterized for downtown Toronto, Ontario, Canada, and run with an illustrative emission rate for selected polycyclic aromatic hydrocarbons and homologues of polychlorinated dibenzodioxins, indicates that the film achieves the highest concentrations among media but that soils are the greatest sink for all but the least hydrophobic chemicals. The film “reflects” the more volatile chemicals into air, facilitates removal to surface waters by wash-off, and provides a surface on which photolytic degradation can occur. As such, the film is a transient sink that increases chemical mobility in urban areas by increasing air concentrations and the cycling of these compounds between air and urban surfaces and increasing water concentrations. Vegetation also accumulates SOCs, a portion of which is transferred to soil that reduces chemical mobility.

Gas/solid partitioning of semivolatile organic compounds (SOCs) to air filters. 2. Partitioning of polychlorinated dibenzodioxins, polychlorinated dibenzofurans, and polycyclic aromatic hydrocarbons to quartz fiber filters

Gas/particle distributions of atmospheric semi-volatile organic compounds (SOCs) are often measured using filter/sorbent samplers. Unfortunately, the adsorption of gaseous SOCs onto a filter can cause positive biases in the measured particle-phase concentrations, and negative biases in the measured gas-phase concentrations. When quartz fiber filters (QFFs) are used, surface-area-normalized gas/quartz partition coefficient ( K p,s, m 3 m −2) values will be useful when estimating the magnitudes of these errors. Gas/QFF K p,s values have been reported in the literature only for polycyclic aromatic hydrocarbons (PAHs) and n-alkanes. Gas/QFF K p,s values were measured here for a series of polychlorinated dibenzodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), and also for a range of PAHs. Within each of the three individual compound classes, plots of log K p,s vs. log p L o (sub-cooled liquid vapor pressure) were found to be linear with slopes of approximately −1. At relative humidity (RH)=25%, the pooled log K p,s data at 25°C for the three compound classes were correlated with log p L o nearly as well ( r 2=0.95) as were the data for the individual compound classes ( r 2≈0.97). In general, the K p,s values for the PAHs and PCDD/PCDFs studied were found to be about a factor of 2 larger for partitioning to clean QFFs at RH=25% than for TMFs at RH=21–52%. Backup QFFs used in filter/sorbent sampling in a suburban area yielded K p,s values for PAHs at RH=37% that were significantly lower than for clean QFFs at the same RH. (This may have been the result of the adsorption of ambient organic compounds that at least partially blocked the direct adsorption of the SOCs to the QFF surface). Therefore, when QFFs are used to separate atmospheric gas- and particle-phase SOCs, corrections for compound-dependent gas adsorption artifacts for QFFs may need to be carried out using K p,s values that were obtained with ambient backup QFFs.