Measurement of the vapor phase deposition of polychlorinated bipheyls (PCBs) using a water surface sampler

A water surface sampler (WSS) was employed in combination with greased knife-edge surface deposition plates (KSSs) to measure the vapor phase deposition rates of PCBs to the sampler at an urban site, Chicago, IL. This sampler employed a water circulation system that continuously removed deposited PCBs. Total (gas+particle) and particulate PCB fluxes were collected with the WSS and KSSs, respectively. Gas phase PCB fluxes were then calculated by subtracting the KSS fluxes (particulate) from the WSS fluxes (gas+particle). The calculated gas phase PCB fluxes averaged 830±910 ng m⁻²d⁻¹. This flux value is, in general, higher than the fluxes determined using simultaneously measured air–water concentrations in natural waters and is in the absorption direction. This difference is primarily because the PCBs were continuously removed from the WSS water keeping the water PCB concentration near zero.Concurrently, ambient air samples were collected using a modified high volume air sampler. The gas phase PCB concentrations ranged between 1.10 and 4.46 ng m⁻³ (average±SD, 2.29±1.28 ng m⁻³). The gas phase fluxes were divided by the simultaneously measured gas phase ambient concentrations to determine the overall gas phase mass transfer coefficients (MTCs) for PCBs. The average gas phase overall MTCs (K_g) for each homolog group ranged between 0.22 and 1.32 cm s⁻¹ (0.54±0.47 cm s⁻¹). The average MTC was in good agreement with those determined using similar techniques.     

Dry deposition fluxes and deposition velocities of PAHs at an urban site in Turkey

Even though dry deposition and air–water exchange of semivolatile organic compounds (SOCs) are important for surfaces in and around the urban areas, there is still no generally accepted direct measurement technique for dry deposition. In this study, a modified water surface sampler (WSS) configuration, including a filter holder and an XAD-2 resin column, was employed to investigate the polycyclic aromatic hydrocarbon (PAH) dry deposition in an urban area. The measured total (particle+dissolved) PAH fluxes to the WSS averaged to be 34 960±16 540 ng m⁻² d⁻¹. Average particulate PAH flux, determined by analyzing the filter in the WSS, was about 8% of the total PAH flux. Temporal flux variations indicated that colder months (October–April) had the highest PAH fluxes. This increase could be attributed to the residential heating as well as meteorological effects including lower mixing height. A high volume air sampler was concurrently employed to collect ambient air concentrations. The average total (gas+particle) atmospheric PAH concentration (456±524 ng m⁻³) was within the range of previously measured values at different urban locations. PAH concentrations in urban areas are more than two orders of magnitude higher than those measured in pristine areas and this result may indicate that urban areas have major source sectors and greater deposition rates are expected near to these areas. The average contribution of particle phase was about 10% in total concentration. Simultaneous particulate phase dry deposition and ambient air samples were collected in this study. Then, particulate phase apparent dry deposition velocities were calculated using the fluxes and concentrations for each PAH compound and they ranged from 0.1 to 1.2 cm s⁻¹. These values are in good agreement with previously reported values.     

Bulk deposition of polycyclic aromatic hydrocarbons (PAHs) in an industrial site of Turkey

Ambient air and deposition samples were collected in the period of July 2004-May 2005 in an industrial district of Bursa, Turkey and analyzed for polycyclic aromatic hydrocarbon (PAH) compounds. The overall average of fourteen bulk deposition fluxes for PAHs was 3300+/-5100 ng m(-2) d(-1). PAH depositions showed a seasonal variation and they were higher in winter months. This was probably due to increases in residential heating activities and decreases in atmospheric mixing layer levels. Ambient air samples, measured with a high volume air sampler, were collected from the same site. The average total concentration including gas and particulate phase was about 300+/-420 ng m(-3) and it was in the range of previously reported values. Some of the ambient air and bulk deposition samples were collected simultaneously in dry periods. Both concurrently measured values were used to calculate the dry deposition velocities whose overall average value was 0.45+/-0.35 cm s(-1).     

The dependence of airborne particulate deposition on atmospheric stability and surface conditions

The deposition of airborne Pb particulates has been experimentally investigated in different fields. Three fields with different surface conditions were selected for which the roughness sizes have been determined under neutral atmospheric conditions. A modified low-pressure Andersen impactor was used to determine the particle-size distribution. The sampler classifies particle size in ultra-fine range down to 0.08 μm aerodynamic diameter. The flux of particulate Pb was measured on the surfaces of: alfalfa leaves, real grass and soil under stable and unstable atmospheric conditions.Data from a meteorological tower were analysed to determine the standard deviation of horizontal wind direction from which the atmospheric stability class was determined. The deposition surfaces were wet-ashed with HNO₃ and analysed for Pb by atomic absorption spectrophotometry and the particulate fluxes were obtained. The particulate fluxes were also calculated from the size-distribution data and values of deposition velocity were obtained from two deposition models (Sehmel and Hodgson, 1978; El-Shobokshy and Sharaf El-Din, 1984).It is concluded that both surface roughness and atmospheric stability are the main controlling factors in particulate deposition, together with particle diameter. For unstable conditions, there was quite good agreement between measured and calculated particulate flux using both of the above theoretical models. For stable conditions, Sehmel and Hodgson's model failed to predict accurate fluxes because their model shows the independence of deposition velocity on atmospheric stability.     

Atmospheric dry deposition fluxes of trace elements measured in Bursa, Turkey

Trace element dry deposition fluxes were measured using a smooth, greased, knife-edge surrogate surface (KSS) holding greased Mylar strips in Bursa, Turkey. Sampling program was conducted between October 2002 and June 2003 and 46 dry deposition samples were collected. The average fluxes of crustal metals (Mg, Ca, and Fe) were one to four orders of magnitude higher than the fluxes of anthropogenic metals. Trace element fluxes ranged from 3 (Cd) to 24,230 (Ca) microg m(-2) d(-1). The average trace element dry deposition fluxes measured in this study were similar to those measured in other urban areas. In addition, ambient air samples were also collected simultaneously with flux samples and concentrations of trace elements, collected with a TSP sampler, were between 0.7 and 4900 ng m(-3) for Cd and Ca, respectively. The overall trace element dry deposition velocities, calculated by dividing the fluxes to the particle phase concentrations ranged from 2.3+/-1.7 cm s(-1) (Pb) to 11.1+/-6.4 cm s(-1) (Ni). These values are in good agreement with the values calculated using similar techniques. The anthropogenic and crustal contributions were estimated by employing enrichment factors (EFs) calculated relative to the average crustal composition. Low EFs for dry deposition samples were calculated. This is probably due to contamination of local dust and its important contribution to the collected samples.     

Atmospheric deposition of polycyclic aromatic hydrocarbons to water surfaces: A mass balance approach

A mass balance model was developed to explain the movement of polycyclic aromatic hydrocarbons (PAH) into and out of Siskiwit Lake, which is located on a wilderness island in northern Lake Superior. Because of its location, the PAH found in this lake must have originated exclusively from atmospheric sources. Using gas Chromatographie mass spectrometry, 11 PAH were quantified in rain, snow, air, lake water, sediment core and sediment trap samples. From the dry deposition fluxes, an aerosol deposition velocity of 0.99 ± 0.15 cm s⁻¹ was calculated for indeno[1,2,3-cd]pyrene and benzo[ghi]perylene, two high molecular weight PAH which are not found in the gas phase. The dry aerosol deposition was found to dominate the wet removal mechanism by an average ratio of 9:1. The dry gas flux was negative, indicating that surface volatilization was taking place; it accounted for 10–80 % of the total output flux depending on the volatility of the PAH. The remaining PAH were lost to sedimentation. From the dry gas flux, an overall mass transfer coefficient for PAH was calculated to be 0.18 ± 0.06 m d⁻¹. In this case, the overall mass transfer is dominated by the liquid phase resistance.     

Overall elemental dry deposition velocities measured around Lake Michigan

Overall dry deposition velocities of several elements were determined by dividing measured fluxes by measured airborne concentrations in different particle size ranges. The dry deposition measurements were made with a smooth surrogate surface on an automated dry deposition sampler (Eagle II) and the ambient particle concentrations were measured with a dichotomous sampler. These long-term measurements were made in Chicago, IL, South Haven, MI, and Sleeping Bear Dunes, MI, from December 1993 through October 1995 as part of the Lake Michigan Mass Balance Study. In general, the dry deposition fluxes of elements were highly correlated with coarse particle concentrations, slightly less well correlated with total particle concentrations, and least well correlated with fine particle concentrations. The calculated overall dry deposition velocities obtained using coarse particle concentrations varied from approximately 12 cm s⁻¹ for Mg in Chicago to 0.2 cm s⁻¹ for some primarily anthropogenic metals at the more remote sites. The velocities calculated using total particle concentrations were slightly lower. The crustal elements (Mg, Al, and Mn) had higher deposition velocities than anthropogenic elements (V, Cr, Cu, Zn, Mo, Ba and Pb). For crustal elements, overall dry deposition velocities were higher in Chicago than at the other sites.     

Dry deposition (downward, upward) concentration study of particulates and heavy metals during daytime, nighttime period at the traffic sampling site of Sha-Lu, Taiwan

Downward, upward dry deposition fluxes and total suspended particulate of particulate heavy metals (Fe, Pb, Zn, Cu, Mg and Mn) were measured in daytime and nighttime period in Sha-Lu, a small city in the central Taiwan during summer period of 2003. The results showed that the total suspended particulate concentrations of particulate mass in the daytime period (averaged 996.2 g/m3) were higher than in nighttime period (averaged 560.7 g/m3). And the downward dry deposition fluxes (averaged 54.07 g/m2s) were about two times as that of upward dry deposition fluxes (averaged 26.48 g/m2s) in the daytime period. Furthermore, the average downward dry deposition fluxes (averaged 26.22 g/m2s) were also about two times as that of upward dry deposition fluxes (averaged 12.11 g/m2s) in the nighttime period. In addition, the average downward dry deposition fluxes are greater than the upward dry deposition fluxes for all the heavy metals in either daytime or nighttime period. The proposed reasons are that the wind speed and concentration difference for daytime and nighttime period lead to these results at the traffic sampling site of central Taiwan. In addition, the deposition velocity for mass, heavy metals (Fe, Pb, Zn, Cu, Mg and Mn) during daytime and nighttime period were also calculated. The average daytime dry deposition velocity for downward particulate mass, upward particulate mass, Fe, Pb, Zn, Cu, Mg and Mn were 5.56, 2.66, 1.71, 0.18, 1.06, 0.24, 0.47 and 0.11 (cm/s), respectively. And the average nighttime dry deposition velocity for downward particulate mass, upward particulate mass, Fe, Pb, Zn, Cu, Mg and Mn were 4.70, 2.11, 1.66, 0.18, 0.86, 0.23, 0.32 and 0.07 (cm/s), respectively at traffic sampling site of central Taiwan.     

Overall dry deposition velocities of trace elements measured at harbor and traffic site in central Taiwan

For reasonable and convenient assessments of the characteristics of the dry deposition velocities between Taichung harbor site and Wuchi town site in central Taiwan, the overall dry deposition velocities of several metallic elements were calculated as the particulate diameter (D(p)) distributions of large particles (D(p) > 10 microm), coarse particles (10 microm < D(p) < 2.5 microm), and fine particles (D(p) < 2.5 microm) based on the ambient measurements during March-December of 2004. In this work, the dry deposition fluxes showed the higher correlation with coarse particle concentrations than large particle concentrations; however, the least well correlation was observed between the dry deposition fluxes and the fine particle concentrations. The calculated best-fit overall dry deposition velocities obtained using coarse particle concentrations varied from approximately 0.2 cm s(-1) for Cr to 1.5 cm s(-1) for Pb and 0.2 cm s(-1) for Fe to 2.6 cm s(-1) for Pb at Taichung harbor and Wuchi town site, respectively. In general, the crustal elements had higher deposition velocities than anthropogenic elements. In addition, overall dry deposition velocities for crustal elements were higher in Wuchi town site than in Taichung harbor site. The results identified the dry deposition flux was mainly contributed from large and coarse particles due to their high deposition velocities. The results also indicated that the best approach to estimate overall dry deposition was by depending on the characteristics of particles with diameters larger than 2.5 microm.     

Apply appropriate models in the study of dry deposition fluxes of particulate matter and polycyclic aromatic hydrocarbons (PAHs) in Tsukuba, Japan

In this study, plates for downward flux and upward flux were used to measure atmospheric dry deposition fluxes for particulate mass and polycyclic aromatic hydrocarbons (PAHs) in TERC (Tsukuba), Japan. Ambient particles concentrations were also collected using a high-volume air sampler, and ambient particle size distributions between 0.01 μm and 13.1 μm were measured using a low-pressure cascade impactor to characterise the PAHs levels and dry deposition. The results indicated that the average cumulative fraction of dry deposition flux for particles and PAHs which attached with them was caused by the particle size of greater than 1.2-6.3 μm (97%).     

Ambient concentrations and dry deposition fluxes of trace elements in Izmir,Turkey

Dry deposition samples were collected using a smooth surrogate surface at the Kaynaklar Campus of the Dokuz Eylul University in Izmir, Turkey. Concurrently ambient aerosol samples were collected. All samples were analyzed for anthropogenic and crustal trace elements. The average trace element concentrations and fluxes measured in this study were generally higher than those reported previously for urban and rural areas. The contribution of local terrestrial and anthropogenic sources were also investigated using enrichment factors (EFs) calculated relative to the local soil. Relatively lower EFs for ambient samples and high ambient concentrations indicated that the local soil was polluted and contributed significantly to ambient trace element concentrations. Deposition samples had higher EFs than the air samples. The EF sequences of trace elements were also different for deposition and ambient samples, probably due to the fact they have different mass median diameters and deposition velocities. The overall dry deposition velocities for trace elements calculated by dividing the particulate fluxes measured with the surrogate surfaces by ambient concentrations ranged from 0.6 (Al) to 6.2 cm s⁻¹ (Fe). The agreement between the experimental dry deposition velocities determined in this study and the previously reported ones using similar techniques for trace elements was good.     

Analysis of atmospheric behavior of PCDDs/PCDFs by a one-compartment box model

The overall atmospheric behavior of PCDDs/PCDFs in the Kanto region, Japan, was simulated by a one-compartment box model. For each homologue the relative significance and temperature dependences of dry deposition, wet deposition, degradation, and advection in both gas and particulate phases were examined and compared. The results of the model calculation suggested that the rates for dry deposition are comparable to those for wet deposition, and the rates for advection are comparable to those for bulk (dry+wet) depositions in the Kanto region. On the other hand, the rates of degradation for PCDDs/PCDFs in the atmosphere in the Kanto region would be negligible. The emission rates and the bulk deposition fluxes in the entire Kanto region estimated by the model calculation based on observed air concentrations were 0.084-0.90 kg-TEQ/month and 0.045-0.43 kg-TEQ/month, respectively. These estimated emission rates and bulk deposition fluxes were slightly higher than the estimated emission rate based on observed emission concentrations and the estimated bulk deposition fluxes based on observed deposition fluxes collected on water deposition surface, respectively. This study showed the model calculation can be available for understanding of the overall atmospheric behavior, verification of the source inventory, and estimation of deposition flux on the actual environment including various deposition surfaces.     

Persistent organic pollutants in snow from European high mountain areas

Snow cores were collected in the catchment area of five remote mountain lakes in Europe. They were analysed for polycyclic aromatic hydrocarbons (PAH), polychlorinated biphenyls (PCB), and organochlorine pesticides, namely DDTs, hexachlorobenzene (HCB) and hexachlorocyclohexanes (HCH). PAH are found in higher amounts in the Tatra and Caledonian mountains, PCB are higher in the Alps and HCH are highest in the Alps and Pyrenees. The qualitative PAH distributions are dominated by low molecular weight compounds, phenanthrene being the most abundant PAH in all but in one site. These compounds also occur predominantly in the gas phase in the atmosphere. Their high abundance in the snowpack witness the occurrence of effective transfer mechanisms from gas to snow flakes. In Starolesnianske (Tatra mountains), a higher contribution of high molecular weight compounds is found. This site exhibits the highest snow PAH and suspended particulate levels. Transformation of the concentration values of these compounds into annual deposition rates and correction for catchment/lake area indicates that in Scandinavia and the Alps a large proportion of PAH incorporation is mediated by snowfallout whereas in the Tatra mountains snow deposition only accounts for a small fraction of the compounds stored in the lake sediments. Among organochlorine compounds, only PCB and HCH have been found above method detection limit in most of the samples. The PCB congener distributions changes significantly between sites, although a predominance of the less chlorinated congeners have generally been observed.     

Concentrations and gas/particle partitioning of PCBs in Chicago

Thirty seven air samples were collected in Chicago, IL from June to October 1995 and analyzed for gas and particle concentrations of polychlorinated biphenyls (PCBs). Lower molecular weight (MW) PCBs dominated the samples and on average 95% of the Sigma50PCB concentration (gas+particulate) was in the vapor phase. Sigma50PCB concentrations were classified based on prevailing winds (lake and land). The Sigma50PCB concentration varied between 0.42 and 5.21 ng/m3 (1.80+/-1.70 ng/m3) for lake and 0.53 and 8.31 ng/m3 (2.41+/-2.15 ng/m3) for land wind directions. Back trajectory analyses suggested that SW of Chicago can be an important local or regional source sector for PCBs. Partitioning between gas and particulate phases was modeled using the Junge-Pankow model. The measured particle phase concentrations for low MW PCBs were lower than those predicted by the model while the opposite was observed for high MW PCBs. Plots of gas/particle partition coefficient (log Kp) vs. subcooled liquid vapor pressure (log pL(0)) had reasonable correlations for individual samples but the slope varied among the samples. Samples that originated from over the lake had higher slopes than samples that originated from over the land.     

PCB in soils and estimated soil-air exchange fluxes of selected PCB congeners in the south of Sweden

PCB concentrations were studied in different soils to determine the spatial variation over a region of approximately 11 000 km(2). PCB congener pattern was used to illustrate the spatial differences, as shown by principal component analysis (PCA). The relationship to different soil parameters was studied. PCB concentrations in soil showed a large variation between sampling-areas with median concentrations ranging between 2.3 and 332 ng g(-1) (dw). Highest concentrations were found at two sites with sandy soils, one with extremely high organic carbon content. Both sites were located on the west coast of southern Sweden. Soils with similar soil textures (i.e. sandy silt moraine) did not show any significant differences in PCB concentrations. PCB congener composition was shown to differ between sites, with congener patterns almost site-specific. PCB in air and precipitation was measured and the transfer of chemicals between the soil and air compartments was estimated. Soil-air fugacity quotient calculations showed that the PCBs in the soil consistently had a higher fugacity than the PCBs in the air, with a median quotient value of 2.7. The gaseous fluxes between soil and air were estimated using standard modelling equations and a net soil-air flux estimated by subtracting bulk deposition from gaseous soil-air fluxes. It was shown that inclusion of vertical sorbed phase transport of PCBs in the soil had a large effect on the direction of the net soil-air exchange fluxes.     

Atmospheric concentrations, occurrence and deposition of persistent organic pollutants (POPs) in a Mediterranean coastal site (Etang de Thau, France)

Atmospheric concentrations and deposition fluxes of PCDD/F and PCB have been evaluated over a 1-year period in a Mediterranean coastal lagoon (Etang de Thau, France). Indicative PBDE air concentrations in the hot season are also reported in this work. ∑2,3,7,8-PCDD/Fs and ∑18PCBs (gas + particulate) air concentrations ranged from 67 to 1700 fg m⁻³ and from 13 to 95 pg m⁻³, respectively whereas ∑8PBDEs (gas + particulate) summer time levels varied from 158 to 230 pg m⁻³. The PCDD/F and PCB atmospheric occurrence over Thau lagoon and subsequent inputs to the surface waters are determined by an assemble of factors, being the seasonality of atmospheric concentration, the air mass origin and meteorological conditions important drivers. Total (wet + dry) ∑2,3,7,8-PCDD/Fs and ∑18PCBs deposition fluxes to Thau Lagoon waters are 117 and 715 pg m⁻² d⁻¹, respectively.     

Polychlorinated biphenyl contamination trends in Lake Hartwell, South Carolina (USA): sediment recovery profiles spanning two decades

To assess the ca. 20-year polychlorinated biphenyl (PCB) contamination trends in Lake Hartwell, SC, sediment cores from the Twelve Mile Creek arm were collected in July 2004 at two sites (G30 and G33) first sampled in the mid-1980s. Congener-specific PCB data as a function of depth from the sediment-water interface for the 2004 sediment samples were compared to data obtained from 1987 and 1998 samples taken from the same locations. Despite modest decreases in total PCB levels near the G30 sediment-water interface, historical increases in average degrees of chlorination may elevate the overall toxic risk at this site. Unlike G30, the more rapid recovery in the near-surface sediment of G33 suggests that the effectiveness of the U.S. EPA natural attenuation record of decision is site-specific and is unlikely to result in uniform surface sediment recovery throughout the most contaminated regions of Lake Hartwell.     

Gas-particle concentration and distribution of n-alkanes and polycyclic aromatic hydrocarbons in the atmosphere of Prato (Italy)

Air samples were collected in an urban and industrialised area of Prato (Italy) during 2002, as part of a study to identify and measure aliphatic hydrocarbons and polycyclic aromatic hydrocarbons (PAHs). Total concentrations of aliphatic hydrocarbons ranged between 170 and 282ngm(-3) in the gas phase and from 48.9 to 276ngm(-3) in the particulate phase. The average total PAH concentrations (gas+particulate) were 59.4+/-26.5ngm(-3), and both gas and particulate phase PAH concentrations decreased with increasing temperature. Source identification using diagnostic ratios and principal component analysis identified automobile traffic, in particular, the strong influence of diesel fuel burning, as the major PAH source. Gas-particle partition coefficients (K(p)'s) of n-alkane and PAHs were well correlated with the sub-cooled liquid vapour pressure (P(L)(0)) and indicate stronger sorption of PAHs to aerosol particles compared with n-alkanes.     

Polychlorinated biphenyls (PCBs) in the atmosphere of sub-alpine northern Italy

The main objective of this work was to assess the atmospheric concentrations and seasonal variations of selected POPs in a sub-alpine location where few data are available. A monitoring and research station was set up at the JRC Ispra EMEP site (Italy). We present and discuss a one-year data set (2005-2006) on PCB air concentrations. ∑7PCBs monthly averaged concentration varied from 31 to 76 pg m⁻³. Concentrations in the gas phase (21-72 pg m⁻³) were higher than those in the particulate phase (3-10 pg m⁻³). Advection of air masses and re-volatilization from local sources seem to play a dominant role as drivers of PCB atmospheric concentrations in the area. Indications of seasonal variation affecting PCB congener patterns and the gas/particulate partitioning were found. Modeling calculations suggest a predominant importance of the wet deposition in this region (1 μg m⁻² yr⁻¹ ∑7PCBs yearly total wet deposition flux; 650-2400 pg L⁻¹ rainwater concentrations).