Atmospheric Semivolatile Organic Compounds Research Articles

Extractable denuders for selective sampling of vapour phase organics in the atmosphere

Extractable denuders were designed to collect trace atmospheric semivolatile organic compounds with high volume (38.30 and 200 L/ min) samplers. Denuders were made of multichannel ceramic support coated with sodium silicate and functionalised with phenyl moieties. Polycyclic aromatic hydrocarbons, polychlorinated biphenyls, polychlorinated dibenzodioxins and polychlorinated dibenzofurans and chlorobenzenes in ambient air of a sub-urban area of Monterotondo, Italy, were sampled. Samplings were of 24 h, 48 h and 1 week period. Precision was determined using field triplicates and compared to the conventional high volume sampler methods. The fraction of analytes in the particle phase measured with the filter/ PUF system ranged from 0.2 % for naphthalene to 98.5 % for benzo(ghi)perylene; this fraction measured with the denuder ranged from 0.5 % for naphthalene to 99.0 % for benzo(ghi)perylene. A paired t-test indicated that these values were significantly (t = 3.58, P < 0.01) higher for the denuder. Results showed good repeatability (0.4–4.6 %), sampling efficiency (>99 %) and good capacity as variations in experimental efficiency were not observed also for longer (1 week) period sampling. As significant changes in efficiency were observed (0.7–5.6 %), the developed denuder cannot be reused more than once. However, it is possible to regenerate the denuder with a new silanization step. A good linear correlation was found plotting the vapour/particle distribution ratio versus the vapour pressure (R2 ranged between 0.59 and 0.84) and versus the octanol/air partition coefficient (R2 ranged between 0.85 and 0.88) of each selected SVOCs, in good agreement with the theoretical models for partitioning of SVOCs.

Role of semi-volatile particulate matter in gas-particle partitioning leading to change in oxidative potential.

Atmospheric semi-volatile organic compounds (SVOCs) are complex in their chemical and toxicological characteristics with sources from both primary combustion emissions and secondary oxygenated aerosol formation processes. In this study, thermal desorption of PM2.5 in association with online measurement of reactive oxygen species (ROS) was carried out to study the role of SVOCs in its gas-particle partitioning. The mass concentrations of PM2.5, black carbon (BC) and p-PAHs downstream of a thermodenuder were measured online at different temperature settings (25, 50, 100, and 200°C) to characterize PM physico-chemical properties. While the mass concentrations of PM2.5 and p-PAHs reduced to ∼34% at 200°C compared to that in ambient temperature, BC mass concentration has decreased by 30% at the highest temperature. Furthermore, the submicron particle size distribution showed reduced particle number concentration in Aitken mode at 200°C heating. The ROS, measured by Particle-into-Nitroxide-Quencher, also showed reduction and followed a similar trend with PM measurements, where the total ROS decreased by 12%, 31%, and 53% at 50°C, 100°C, and 200°C, respectively, compared to the ambient sample. When a HEPA filter was included in the upstream of samples, 39% of gas phase ROS reduction was observed at 200°C. This provided a good estimate of the contribution of SVOCs in ROS production in PM2.5, where decreased SVOCs concentration at 200°C increased the percentage of particle surface area. This concludes that the surface chemistry of these organic coatings on the particles is important for assessing the health impacts of PM.

Gas/particle partitioning of semi-volatile organic compounds in the atmosphere: Transition from unsteady to steady state

We derive differential equations to determine the kinetics of gas/particle partitioning of semi-volatile organic compounds (SVOCs). These equations model the transient states from initiation of sorption to particles (non-steady state) through the establishment of steady state. Two hypothetical scenarios are examined: (1) exchange of SVOCs between gas- and particle-phases alone; and (2) both gas/particle partitioning and wet and dry deposition of particles. The differential equations show that, under Scenario 1, a steady state is reached as an equilibrium between gas- and particle-phases, whereas under Scenario 2, the attained steady state is not in equilibrium. Our model shows that SVOCs in atmosphere where particle deposition is occurring reach a steady non-equilibrium state sooner than they would reach equilibrium under Scenario 1. We infer that SVOCs in the atmosphere will reach steady state instead of equilibrium between gaseous and particulate phases in circumstances where wet and dry deposition of particles cannot be neglected. In addition, our study indicates that the time for SVOCs to reach steady state in the atmosphere is fast, most likely within minutes or hours, suggesting that SVOCs are in steady or quasi-steady state in the atmosphere. Our analysis also reveals that gas/particle partitioning and particle deposition of SVOCs are dependent on each other.

Constituents of Atmospheric Semi-Volatile and Intermediate Volatility Organic Compounds and Their Contribution to Organic Aerosol

Constituents of Atmospheric Semi-Volatile and Intermediate Volatility Organic Compounds and Their Contribution to Organic Aerosol

Multi-component determination of atmospheric semi-volatile organic compounds in soils and vegetation from Tarragona County, Catalonia, Spain

Tarragona County (Spain) is home to the most important chemical/petrochemical industrial complex in Southern Europe, which raises concerns about the presence and effects of the numerous environmental contaminants. In order to assess the levels and patterns of five classes of semi-volatile organic compounds (SVOCs) - polycyclic aromatic hydrocarbons (PAHs), synthetic musks (SMs), polychlorinated biphenyls (PCBs), brominated flame retardants (BFRs) and one organochlorine pesticide, hexachlorobenzene (HCB), 27 samples of soil and vegetation (Piptatherum L.) from different areas (petrochemical, chemical, urban/residential, and background) of Tarragona County were analysed. The results show that PAHs levels in soils ranged from 45.12 to 158.00ng/g and the urban areas presented the highest concentrations, mainly associated with the presence of a nearby highway and several roads with heavy traffic. PAHs levels in vegetation samples ranged from 42.13 to 80.08ng/g, where the greatest influence came from the urban and petrochemical areas. In the case of SMs, levels in soils and vegetation samples ranged from 5.42 to 10.04ng/g and from 4.08 to 17.94ng/g, respectively, and in both cases, background areas (at least 30km away from the main SVOCs emission sources) showed the highest levels, suggesting an influence of the personal care products derived from beach-related tourism in the coast. PCBs (from 6.62 to 14.07ng/g in soils; from 0.52 to 4.41ng/g in vegetation) prevailed in the chemical area in both matrices, probably associated with the presence of two sub-electrical stations located in the vicinities. In general terms, BFRs and HCB values recorded in soil and vegetation samples were quite similar between matrices and sampling areas.

Assessing atmospheric concentration of polychlorinated biphenyls by evergreen Rhododendron maximum next to a contaminated stream.

Conifers are often used as an air passive sampler, but few studies have focused on the implication of broadleaf evergreens to monitor atmospheric semivolatile organic compounds such as polychlorinated biphenyls (PCBs). In the present study, the authors used Rhododendron maximum (rhododendron) growing next to a contaminated stream to assess atmospheric PCB concentrations. The present study area was located in a rural setting and approximately 2 km downstream of a former capacitor plant. Leaves from the same mature shrubs were collected in late fall 2010 and winter and spring 2011. Polychlorinated biphenyls were detected in the collected leaves, suggesting that rhododendron can be used as air passive samplers in rural areas where active sampling is impractical. Estimated ΣPCB (47 congeners) concentrations in the atmosphere decreased from fall 2010 to spring 2011 with concentration means at 3990 pg m(-3) , 2850 pg m(-3) , and 931 pg m(-3) in fall 2010, winter 2011, and spring 2011, respectively. These results indicate that the atmospheric concentrations at this location continue to be high despite termination of active discharge from the former industrial source. Leaves had a consistent pattern of high concentrations of tetra-CBs and penta-CBs similar to the congener distribution in polyethylene passive samplers deployed in the water column, suggesting that volatilized PCBs from the stream were the primary source of contaminants in rhododendron leaves. Environ Toxicol Chem 2016;35:2192-2198. © 2016 SETAC.

Images reveal that atmospheric particles can undergo liquid–liquid phase separations

A large fraction of submicron atmospheric aerosol particles contains both organic material and inorganic salts. As the relative humidity cycles in the atmosphere and the water content of the particles correspondingly changes, these mixed particles can undergo a range of phase transitions, possibly including liquid-liquid phase separation. If liquid-liquid phase separation occurs, the gas-particle partitioning of atmospheric semivolatile organic compounds, the scattering and absorption of solar radiation, and the reactive uptake of gas species on atmospheric particles may be affected, with important implications for climate predictions. The actual occurrence of liquid-liquid phase separation within individual atmospheric particles has been considered uncertain, in large part because of the absence of observations for real-world samples. Here, using optical and fluorescence microscopy, we present images that show the coexistence of two noncrystalline phases for real-world samples collected on multiple days in Atlanta, GA as well as for laboratory-generated samples under simulated atmospheric conditions. These results reveal that atmospheric particles can undergo liquid-liquid phase separations. To explore the implications of these findings, we carried out simulations of the Atlanta urban environment and found that liquid-liquid phase separation can result in increased concentrations of gas-phase NO(3) and N(2)O(5) due to decreased particle uptake of N(2)O(5).

Spatial variability of atmospheric semivolatile organic compounds in Chile

Abstract In an effort to characterize the spatial variability of pesticides, polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAHs) in the Chilean atmosphere, XAD-based passive air samplers (PAS) were deployed for 12 months (2006–2007) along three elevational gradients in Northern, Central and Southern Chile, for a total of 20 sampling sites, ranging in elevation from 10 to 4400 m and ranging over 26 degrees of latitude. Hexachlorobenzene (HCB) had largely uniform air concentrations with latitude and altitude, and is therefore used to derive sampler specific sampling rates, that account for differences in uptake kinetics due to environmental factors such as altitude and temperature. Levels of pesticides in the atmosphere of Chile are very low and only α- and γ-hexachlorocyclohexane, α-endosulfan and chlorothalonil were present in all of the samples. The concentrations of these four pesticides in air decreased from North to South, with much steeper gradients for chlorothalonil and endosulfan. Chlorothalonil levels were greatly elevated in air samplers deployed in urban locations. Endosulfan concentrations in air tend to increase with elevation. Since endosulfan is particularly susceptible to mountain cold-trapping, such gradients may reflect the re-volatilization of endosulfan that had been preferentially deposited at higher altitudes. Alternatively, increasing endosulfan concentrations with elevation could be the result of transport to higher altitude sites from the other side of Andes. Airshed analysis indeed indicates that air masses originating outside of Chile have a higher influence on the higher elevation sites, especially along the Northern transect. Concentrations of four-ring PAHs ranged from 0.3 to 1300 pg m −3 , with higher levels in air samplers deployed in urban areas and close to roads. PCB concentrations were low (0.7–27 pg m −3 ), with slightly higher levels of volatile congeners in two urban sampling sites in Concepcion and Arica. PCB-52 is the only congener present in all samples, with levels that are remarkably uniform across the country.

Performance of a High Flow Rate, Thermally Extractable Multicapillary Denuder for Atmospheric Semivolatile Organic Compound Concentration Measurement

A high flow rate (300 L min(-1)) multicapillary denuder was designed to collect trace atmospheric semivolatile organic compounds (SOCs). The denuder is coated with a reusable, polydimethylsiloxane stationary phase as a nonselective absorbent for SOCs. A solvent-free thermal desorption method was developed, including sample cleanup, that is selective for nonpolar SOCs, and has low consumables cost per sample. The entire sample is transferred into the gas chromatograph to minimize the sampling time required to collect detectable analyte mass. Trace concentrations (0.1-100 pg m(-3)) of polychlorinated biphenyls and hexachlorobenzene were measured in the atmosphere near Lake Superior in sample times of 3.2-6.2 h. Overall method precision was determined using field duplicates and compared to the conventional high-volume sampler method. Method precision (coefficient of variation) of 16% was found for the high-flow denuder compared to 21% for the high-volume method. The relative difference between the two methods was 25%, with the high-flow denuder method giving generally lower concentrations. The high-flow denuder is an alternative to high-volume or passive samplers when it is desirable to separate gaseous from particle-associated SOCs upstream of a filter. The method is advantageous for studies that require high temporal resolution.

In situ measurements of gas/particle-phase transitions for atmospheric semivolatile organic compounds

An understanding of the gas/particle-phase partitioning of semivolatile compounds is critical in determining atmospheric aerosol formation processes and growth rates, which in turn affect global climate and human health. The Study of Organic Aerosol at Riverside 2005 campaign was performed to gain a better understanding of the factors responsible for aerosol formation and growth in Riverside, CA, a region with high concentrations of secondary organic aerosol formed through the phase transfer of low-volatility reaction products from the oxidation of precursor gases. We explore the ability of the thermal desorption aerosol gas chromatograph (TAG) to measure gas-to-particle-phase transitioning for several organic compound classes (polar and nonpolar) found in the ambient Riverside atmosphere by using in situ observations of several hundred semivolatile organic compounds. Here we compare TAG measurements to modeled partitioning of select semivolatile organic compounds. Although TAG was not designed to quantify the vapor phase of semivolatile organics, TAG measurements do distinguish when specific compounds are dominantly in the vapor phase, are dominantly in the particle phase, or have both phases present. Because the TAG data are both speciated and time-resolved, this distinction is sufficient to see the transition from vapor to particle phase as a function of carbon number and compound class. Laboratory studies typically measure the phase partitioning of semivolatile organic compounds by using pure compounds or simple mixtures, whereas hourly TAG phase partitioning measurements can be made in the complex mixture of thousands of polar/nonpolar and organic/inorganic compounds found in the atmosphere.

Prediction of gas collection efficiency and particle collection artifact for atmospheric semivolatile organic compounds in multicapillary denuders

A modeling approach is presented to predict the sorptive sampling collection efficiency of gaseous semivolatile organic compounds (SOCs) and the artifact caused by collection of particle-associated SOCs in multicapillary diffusion denuders containing polydimethylsiloxane (PDMS) stationary phase. Approaches are presented to estimate the equilibrium PDMS–gas partition coefficient ( K pdms) from a solvation parameter model for any compound, and, for nonpolar compounds, from the octanol–air partition coefficient ( K oa) if measured K pdms values are not available. These estimated K pdms values are compared with K pdms measured by gas chromatography. Breakthrough fraction was measured for SOCs collected from ambient air using high-flow (300 L min −1) and low-flow (13 L min −1) denuders under a range of sampling conditions (−10 to 25 °C; 11–100% relative humidity). Measured breakthrough fraction agreed with predictions based on frontal chromatography theory using K pdms and equations of Golay, Lövkvist and Jönsson within measurement precision. Analytes included hexachlorobenzene, 144 polychlorinated biphenyl congeners, and polybrominated diphenyl ethers 47 and 99. Atmospheric particle transmission efficiency was measured for the high-flow denuder (0.037–6.3 μm diameter), and low-flow denuder (0.015–3.1 μm diameter). Particle transmission predicted using equations of Gormley and Kennedy, Pich, and a modified filter model, agreed within measurement precision (high-flow denuder) or were slightly greater than (low-flow denuder) measured particle transmission. As an example application of the model, breakthrough volume and particle collection artifact for the two denuder designs were predicted as a function of K oa for nonpolar SOCs. The modeling approach is a necessary tool for the design and use of denuders for sorptive sampling with PDMS stationary phase.

Novel sampling methods for atmospheric semi-volatile organic compounds (SOCs) in a high altitude alpine environment

High- and low-volume active air samplers as well as bulk deposition samplers were developed to sample atmospheric SOCs under the adverse conditions of a mountain environment. Active sampling employed separate filters for different European source regions. Filters were switched depending on daily trajectory forecasts, whose accuracy was evaluated post hoc. The sampling continued on three alpine summits over five periods of four months. The prevailing trajectories varied stronger between sampling periods than between stations. The sampling equipment (active and bulk deposition) proved dependable for operation in a mountain environment, with idle times being mainly due to non-routine manipulations and connectivity.

Gas-phase cleanup method for analysis of trace atmospheric semivolatile organic compounds by thermal desorption from diffusion denuders

A novel gas-phase cleanup method was developed for use with a thermal desorption method for analysis of trace semivolatile organic compounds (SOCs) in the atmosphere using diffusion denuder samplers to separate gas-phase from particle-associated fractions. The cleanup selectively removed hydrogen-bonding chemicals from samples, including much of the background matrix of oxidized organic compounds that is present in ambient air samples. Abraham solvation parameters were found to be useful predictors of recovery of compounds through the cleanup method; most compounds with A + B < 0.3 and L ≤ 12.3 were fully recovered through the cleanup method. Addition of the cleanup method successfully produced baseline resolution in air samples and improved method precision. The utility of the method was demonstrated in an investigation of the built environment as a continuing source of semivolatile persistent, bioaccumulative, and toxic chemicals (PBTs) to the atmosphere.

Contributions of deposited particles to pine needle polycyclic aromatic hydrocarbons

The contributions of deposited particles (P) to polycyclic aromatic hydrocarbon (PAH) levels in pine (Cedrus deodar) needles sampled from the Dalian region were evaluated by washing off the particles from pine needle surfaces. P values ranged from 4.4 +/- 2.2% for fluorene to 69.9 +/- 4.0% for indeno(1,2,3-cd)pyrene, and positively correlated with the logarithm of octanol-air partition coefficients (log K OA) of each PAH significantly. P and the total levels of 14 PAHs under study ( summation PAHs), that ranged from 490 to 3241 ng g(-1) dw (dry weight) with median value of 1521 ng g(-1) dw, were high for traffic areas, and low for residential or park areas, implying the significant contributions of PAHs in both gas and particle phases emitted by vehicles. However, PAH profiles in pine needles were not significantly altered by the washing, due to the low fractions (2-5%) of the 5- and 6-ring PAHs in summation PAHs. The high wind speed and frequently alternating wind directions in the Dalian spring could quicken the depuration processes of pine needle PAHs. Thus, the local meteorological conditions and source variations should be taken into account when using pine needles to implicate seasonal variations of atmospheric semi-volatile organic compounds.

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.

Sampling and Analysis of Organic Compounds in Diesel Particulate Matter

The fraction of atmospheric semi-volatile organic compounds (SVOC) is partitioned between the gaseous and particulate phases. Certain of these compounds eg. polynuclear aromatic hydrocarbons (PAH) and their derivatives have been shown to exhibit mutagenic or carcinogenic properties. Emissions from diesel engines are an important source of these contaminants. In a dilution chamber, we studied a diesel engine emissions. It is shown firstly, that the gaseous fraction is predominant (by up to 20 times) with respect to the particulate phase. Secondly, the polar compounds, neglected in the majority of previous studies, are the predominant species. A test campaign was carried out in Paris-Porte d'Auteuil which yielded similar results to the laboratory experiments.

Gas/Particle Partitioning of Semivolatile Organic Compounds To Model Inorganic, Organic, and Ambient Smog Aerosols

Gas/particle (G/P) partitioning is an important process that affects the deposition, chemical reactions, long-range transport, and impact on human and ecosystem health of atmospheric semivolatile organic compounds (SOCs). Gas/particle partitioning coefficients (Kp) were measured in an outdoor chamber for a group of polynuclear aromatic hydrocarbons (PAHs) and n-alkanes sorbing to three types of model aerosol materials: solid ammonium sulfate, liquid dioctyl phthalate (DOP), and secondary organic aerosol (SOA) generated from the photooxidation of whole gasoline vapor. Kp values were also measured for ambient n-alkanes sorbing to urban particulate material (UPM) during summer smog episodes in the Los Angeles metropolitan area. Based on the Kp values obtained for the aerosols studied here, for environmental tobacco smoke (ETS), and for a quartz surface, we conclude that G/P partitioning of SOCs to UPM during summer smog episodes is dominated by absorption into the organic fraction in the aerosol. Comparison...

Vegetation-Atmosphere Partitioning of Polycyclic Aromatic Hydrocarbons

The partitioning of polycyclic aromatic hydrocarbons (PAH) between vegetation and the atmosphere was studied throughout the growing season and under natural conditions. A vegetation-atmosphere partition coefficient (K[sub v]) was derived by analogy to partition coefficients for gas-particle partitioning and fish-water partitioning. K[sub v] is temperature dependent, and from this functional relationship we calculated PAH-vegetation binding energies. These energies were highly correlated with heats of vaporization. The PAH-vegetation partitioning process is primarily dependent upon the atmospheric gas-phase PAH concentration and ambient temperature. At low ambient temperatures (spring and fall) gas-phase PAH partition into vegetation, and at high ambient temperatures (summer), some PAH volatilize and return to the atmosphere. This study provides further evidence that atmospheric semivolatile organic compounds undergo an annual partitioning cycle with the surface of the earth. 39 refs., 3 figs., 1 tab.