Distribution Of Semivolatile Organic Compounds Research Articles

Gas–particle partition and spatial characteristics of polycyclic aromatic hydrocarbons in ambient air of a prototype coking plant

This study investigated the gas–particle partition and spatial characteristics of polycyclic aromatic hydrocarbons (PAHs) in the ambient air of a prototype coking plant. High-volume samplers with glass fiber filters (GFFs) and polyurethane foams (PUFs) were used to collect PAHs in both gaseous and particulate phases. The EPA's 16 priority-controlled PAHs were measured using gas chromatography equipped with a mass-selective detector (GC-MS). The total PAH concentrations ranged from 1.32 μg m−3 to 9.41 μg m−3, with an average of 4.20 μg m−3. PAH abundance at the various sites of the coking plant was determined to be in the following order: coke side > machine side > leeward site; the lowest values were at the reference site and factory boundary. The medium-molecular-weight PAHs had the highest fraction at the coke side, whereas the low-molecular-weight PAHs were predominant at other sampling sites. Considerable amount of chrysene was detected at the coke side, fluorene at the machine side, acenaphthene at the leeward site (240 m downwind of the coke oven), and naphthalene at the other three sites. The gaseous fractions of PAHs at the six sampling sites ranged from 46.3% to 85.8% of the total PAHs in the gas–particle systems; and gaseous PAHs were predominant in the ambient air of the coking plant—except for the coke side, where the PAHs were dominantly partitioned to the particles. In addition, the particulate benzo(a)pyrene equivalence (BaPeq) fraction was high in the coking plant air. The slope (mr) values ranged from −0.59 to −0.39 in the plant, indicating that the absorption mechanism, rather than the adsorption mechanism, dominated the gas–particle partitioning. The intercept (br) values carry the information on the gaseous–particulate phase distribution of semivolatile organic compounds when the mr values are similar. The organic matter fraction in particles, particulate phase fraction of PAHs, and toxicity of particulate matter were found to increase with an increase in br values at similar mr values. The predominant mechanism was absorption for dibenz(a,h)anthracene, benzo(ghi)perylene, and indeno(1,2,3-cd)pyrene, but adsorption for benzo(b)fluoranthene, benzo(a)pyrene, and benzo(k)fluoranthene at the coke and machine sides. By contrast, for most high-molecular-weight PAHs, absorption into the organic matter was the predominant mechanism at other sites. The gas–particle partitioning mechanism of individual PAHs was closely related to the distance from the coke oven, rather than the orientation to the oven. These results may be of great importance in understanding the pollutant process and atmospheric transport of PAHs and may provide guidance to decision makers regarding air pollution control.

Predicting the Gas/Particle Distribution of SVOCs in the Indoor Environment Using Poly Parameter Linear Free Energy Relationships.

Understanding the partitioning of semi volatile organic compounds (SVOCs) between gas phase and particle phase is essential for exposure analysis and risk assessment in the indoor environment. Numerous attempts have been made to calculate gas/particle partitioning coefficients Kip. Single-parameter adsorption and absorption models, which relate Kip to the vapor pressure Ps or the octanol/air distribution coefficient KOA are usually applied. In this work we use poly parameter Linear Free Energy Relationships (pp-LFER) to describe the partitioning behavior of 14 SVOCs with high relevance for the indoor environment. The pp-LFER concept is based on Abraham descriptors and considers interactions between molecule and particle by separate parameters. van der Waals interactions can be approximated by the logarithm of the hexadecane/air partitioning coefficient (log KHdA = L), which is a key parameter for the 14 polar but nonionizable organic esters being studied here. For many of the examined compounds experimentally determined L-values were not available and had to be measured using gas chromatography. It is shown that the pp-LFER method is a strong alternative to single-parameter approaches and gives reliable coefficients for gas/particle distribution in the indoor environment.

Towards improved comparability of studies addressing atmospheric concentrations of semivolatile organic compounds based on their sequestration in pine needles

Coniferous needles can be used as a passive air sampler of semivolatile organic compounds (SVOC) and an indicator of atmospheric pollution patterns and trends. There is limited information on whether different parts of the plant (e.g., foliage leaves, dwarf shoots, twig, etc.) contain different levels of SVOC. Only few studies have compared levels of SVOC surface layer of wax and to their total content in all needle tissues and what affects an uptake and distribution of SVOC. It is important to have better understanding of the extent to which sampling and sample preparation procedures affect measured levels of SVOC in pine needles and reduce comparability of data from samples processed in different ways. In the present study, we assessed an impact of various sampling and sample preparation techniques on the levels of SVOC in Pinus sylvestris needles. While the impact of various storing, washing and drying methods was not significant, presence of dwarf shoots in the sample or structural damage of needles affected the results significantly. Results show that levels of SVOC in dwarf shoots are 2–8 times higher than those in foliage leaves. Therefore, dwarf shoots must be carefully removed before foliage leaves extraction to improve comparability of results. There were different patterns in SVOC on the surface of the foliage leaves compared to the whole leaves. An uptake of these substances by the surface wax as well as their occurrence in the internal structure was of function of the physico-chemical properties of the substances (log Kow, molar weight).

New screening approach for risk assessment of pesticides in ambient air

We present a novel screening approach for inhalation risk assessment of currently used pesticides (CUPs) in ambient air, based on the measurements of pesticide levels in the inhalable fraction of the particulate matter (PM10). Total concentrations in ambient air (gas + particle phases) were estimated using a theoretical model of distribution of semi-volatile organic compounds between the gas and the particulate phase based on the octanol–air partition (Koa) of each pesticide. The proposed approach was used in a pilot study conducted in a rural station in Valencia (Spain) from April through to October 2010. Twenty out of 82 analysed pesticides were detected in average concentrations ranging from 1.63 to 117.01 pg m−3. For adults, children and infants the estimated chronic inhalation risk, expressed as Hazard Quotient (HQ) was <1 for all pesticides. Likewise, the cumulative exposure for detected organophosphorus, pyrethroids and carbamates pesticides, was estimated using as metrics the Hazard Index (HI), which was less than 1 for the three families of pesticides assessed. The cancer risk estimated for the detected pesticides classified as Likely or Possible carcinogens was less than 1.15E-7 for infants. In our opinion, the screening approach proposed could be used in the monitoring and risk assessment of pesticides in ambient air.

A Framework for Modelling Non-Steady-State Concentrations of Semivolatile Organic Compounds Indoors – I: Emissions from Diffusional Sources and Sorption by Interior Surfaces

Over the past two decades, more than 20 mass transfer models have been developed for building materials, furnishings, and consumer products as contaminant sources, sinks, and barriers. While these models have greatly improved our understanding of contaminant movements in buildings, their applications in the real world have been somewhat limited because of the incompatibility and computational complexity of the models. In this paper, a framework is proposed for modelling the dynamic concentrations of semivolatile organic compounds in indoor media. Based on a discretization method, which transfers continuous models into discrete counterparts, this framework can perform the functions of the existing mass transfer models and, at the same time, solves the model incompatibility problem and reduces the computational complexity. This framework complements and supplements the existing multimedia semivolatile organic compound models by providing more details of the distribution of semivolatile organic compounds among indoor media, helping check the validity of certain assumptions that have been used in those steady-state models, and providing more flexibility to allow evaluation of risk management options such as source removal, encapsulation, and variable ventilation rate. This framework will be described in two parts. Part I, this paper, discusses the representation of diffusional sources and sorption by interior surfaces. Interactions of semivolatile organic compounds with particulate matter will be discussed in a subsequent publication.

Vegetation/Soil Distribution of Semivolatile Organic Compounds in Relation to Their Physicochemical Properties

The concentrations (C) of several semivolatile organic compounds (SOCs) in Norway spruce needles (N) and in the local humus horizon (O) of 25 remote Austrian forest sites were used to calculate an ecosystem-oriented partition coefficient needles/humus horizon (CN/CO). Between 66 and 78% of the compounds' variation of this quotient could be explained by each of the following physicochemical parameters: vapor pressure (pS) and the partition coefficients n-octanol/water (KOW), n-octanol/air (KOA), and adsorbed/dissolved in soil (KOC) of the compounds. This result further underlines the usefulness of these parameters for predicting the behavior of SOCs in terrestrial ecosystems. Compounds with low pS and high KOW, KOA, and KOC show a very low CN/CO quotient, which implies a higher accumulation of these compounds in the O horizon than in the needles. The role of forest soils as sink for these SOCs is demonstrated. Alternatively, CN/CO > 1, due to higher concentrations in the needles than in the O horizon, have been shown for SOCs with comparably high pS and low KOW, KOA, and KOC. In this respect, the possible role of revolatilization of the more volatile SOCs from soils to needles is discussed. In the mineral soil layers below the O horizon, SOCs with lower KOC and better water solubility tend to be less accumulated. However, if all investigated compounds are taken into consideration, accumulation in the mineral soil layers showed no general trend in relation to the selected physicochemical parameters.

Measuring and modelling the vertical distribution of semi-volatile organic compounds in soils. II: model development

A dynamic air-soil exchange model which divides the soil into multiple soil layers has been developed and used to simulate the vertical distribution of PCBs in an undisturbed grassland soil. An historical emission profile for PCBs to the UK atmosphere was used to deduce concentrations in the air compartment. Model simulations were tuned by varying the most uncertain model input parameters, namely soil turnover rates by bioturbation and emission estimates. Comparison of model output and reported PCB concentration profiles agreed within a factor of six. Insights were gained into the relative importance of the soil transport processes and specifically bioturbation was shown to be the dominant transport mechanism for PCBs in this soil. It was concluded that the model is sufficiently accurate for incorporation into regional mass balance models, although vertical layering of the soil may be unnecessary in models describing the long-term air-soil interaction of organic compounds.

Measuring and modelling the vertical distribution of semi-volatile organic compounds in soils. I: PCB and PAH soil core data

Soil cores were collected from undisturbed soils at four locations in the UK and analysed for PCBs, PAHs and soil organic carbon. In all four soil cores ΣPCB and ΣPAH concentrations peaked at or just below the soil surface and declined with depth. Statistically significant correlations were obtained between compound concentrations and organic carbon content in all four soil cores. PAH and PCB homologue profiles at different soil depths and horizons provided information on transport of the compounds in the soils. Fairly constant homologue profiles with depth in the cores suggested that bioturbation may be an important soil transport process for PCBs and PAHs.

Airborne lipophilic pollutants in pine needles

Many environmental contaminants known today are semivolatile organic compounds (SOC) and are present in the atmosphere. Airborne SOC are taken up and enriched by the epicuticular wax that covers leaves of higher plants. The purpose of the present work was to use pine needles 1) to map the distribution of airborne SOC in Europe, 2) to identify source regions, and 3) to identify hitherto unknown anthropogenic and/or natural substances. Some of the results were a confirmation of a suspected release of DDT in the former East Germany, high levels of pentachlorophenol were noted in Scandinavia, hexachlorocyclohexanes were higher in southern than in northern Europe, whereas PCB and hexachlorbenzene were rather evenly distributed throughout Europe. Elemental sulphur was identified as a previously unknown natural substance in higher plants.

Organic, elemental, and isotopic tracers of air pollution sources in Albuquerque, NM

Abstract To explore the use of organic compounds as tracers for air pollution sources, data for radiocarbon, trace elements, carbon, and low-polarity organic compounds were obtained for Albuquerque, NM, in December 1985. Measurement of radiocarbon in the organic fraction permitted unambiguous discrimination of modern carbon (wood burning) and fossil carbon (motor vehicle emissions). Modern and fossil carbon co-varied at night, but during the day, modern carbon was correlated with retene, a proposed tracer for softwood combustion. Similar diurnal differences were observed in a multiple linear regression of elemental tracers of woodsmoke and motor vehicle emissions. Using a physical adsorption model, the gas particle distribution of semi-volatile organic compounds in the samples was estimated. The results suggest that, for some compounds, distribution between the gas and particle phases may act as a third “source” affecting measured particulate concentrations. Supporting this conclusion, a factor analysis of the daytime data gave three factors associated with woodsmoke, motor vehicles, and volatile species, respectively.

The distribution of semivolatile organic compounds in conifer needles following gas phase contamination

Spruce needles (Picea abies) which had been exposed for 6 hours to elevated concentrations of gaseous SOC were immersed in dichloromethane for up to 100 minutes. It was found that compounds with higher molecular weights (PCBs, DDT and DDE) were completely removed from the needles after washing for several minutes. Large fractions of the compounds with lower molecular weight (chlorobenzenes and hexachlorocyclohexanes) could not be extracted by this method, even after immersion for 100 minutes. These results are attributed to differences in the diffusion behavior of the two substance groups. For the SOC with higher molecular weights the cuticular lipids act both as a sink and as a diffusion barrier, whereas the SOC with lower molecular weight can readily penetrate into the interior of the needle. These results question contaminant models which assume that the leaf is a single, well mixed compartment. The solvent immersion extraction may be useful when employing needles as biomonitors, possibly circumventing the problem of very slow kinetic behavior in the whole needle.

Determination of the particle size distribution and chemical composition of semi-volatile organic compounds in atmospheric fine particles with a diffusion denuder sampling system

Abstract Correct assessment of the factors associated with visibility impairment is dependent on accurate determination of the chemical composition as a function of size of particles present in the atmosphere. Collection of particles on a filter results in underestimation of particulate organic compounds due to losses from the semi-volatile organic fraction during sample collection, i.e. a “negative sampling artifact”. These semi-volatile organic compounds lost from particles collected on a filter can be correctly measured using a diffusion denuder sampling system. This paper describes a multi-system, multi-channel, high-volume diffusion denuder sampler for the accurate determination of the particle size distribution and chemical composition of semi-volatile organic compounds in atmospheric fine particles. Data obtained in Provo, UT and Los Angeles, CA on the chemical composition and particle size distribution of semi-volatile organic compounds in atmospheric fine particles indicate that the majority of the semi-volatile organic compounds lost from particles during sampling were present in particles in the 0.4–0.8 μm size range in the atmospheres sampled. Organic compounds lost from the particles during sampling include paraffinic compounds, aromatic compounds and organic acids and esters.