Exchange Of Polycyclic Aromatic Hydrocarbons Research Articles

Concentrations, Trends, and Air-Water Exchange of PAHs and PBDEs Derived from Passive Samplers in Lake Superior in 2011.

Polycyclic aromatic hydrocarbons (PAHs) and polybrominated diphenylethers (PBDEs) are both currently released into the environment from anthropogenic activity. Both are hence primarily associated with populated or industrial areas, although wildfires can be an important source of PAHs, as well. Polyethylene passive samplers (PEs) were simultaneously deployed in surface water and near surface atmosphere to determine spatial trends and air-water gaseous exchange of 21 PAHs and 11 PBDEs at 19 sites across Lake Superior in 2011. Surface water and atmospheric PAH concentrations were greatest at urban sites (up to 65 ng L(-1) and 140 ng m(-3), respectively, averaged from June to October). Near populated regions, PAHs displayed net air-to-water deposition, but were near equilibrium off-shore. Retene, probably depositing following major wildfires in the region, dominated dissolved PAH concentrations at most Lake Superior sites. Atmospheric and dissolved PBDEs were greatest near urban and populated sites (up to 6.8 pg L(-1) and 15 pg m(-3), respectively, averaged from June to October), dominated by BDE-47. At most coastal sites, there was net gaseous deposition of BDE-47, with less brominated congeners contributing to Sault Ste. Marie and eastern open lake fluxes. Conversely, the central open lake and Eagle Harbor sites generally displayed volatilization of PBDEs into the atmosphere, mainly BDE-47.

The effects of rice canopy on the air–soil exchange of polycyclic aromatic hydrocarbons and organochlorine pesticides using paired passive air samplers

The rice canopy in paddy fields can influence the air–soil exchange of organic chemicals. We used paired passive air samplers to assess the exchange of polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCPs) in a paddy field, South China. Levels of OCPs and light PAHs were generally higher under the canopy than above it. We found that the rice canopy can physically obstruct the evaporation of most OCPs and light PAHs, and can also act as a barrier to the gaseous deposition of p,p'-DDT and heavy PAHs. Paddy fields can behave as a secondary source of OCPs and light PAHs. The homolog patterns of these two types of chemical varied slightly between the air below and above the rice canopy, implying contributions of different sources. Paired passive air samplers can be used effectively to assess the in situ air–soil exchange of PAHs and OCPs in subtropical paddy fields.

Atmospheric partitioning and the air–water exchange of polycyclic aromatic hydrocarbons in a large shallow Chinese lake (Lake Chaohu)

The residual levels of polycyclic aromatic hydrocarbons (PAHs) in the atmosphere and in dissolved phase from Lake Chaohu were measured by (GC–MS). The composition and seasonal variation were investigated. The diffusive air–water exchange flux was estimated by a two-film model, and the uncertainty in the flux calculations and the sensitivity of the parameters were evaluated. The following results were obtained: (1) the average residual levels of all PAHs (PAH16) in the atmosphere from Lake Chaohu were 60.85±46.17ngm−3 in the gaseous phase and 14.32±23.82ngm−3 in the particulate phase. The dissolved PAH16 level was 173.46±132.89ngL−1. (2) The seasonal variation of average PAH16 contents ranged from 43.09±33.20ngm−3 (summer) to 137.47±41.69ngm−3 (winter) in gaseous phase, from 6.62±2.72ngm−3 (summer) to 56.13±22.99ngm−3 (winter) in particulate phase, and 142.68±74.68ngL−1 (winter) to 360.00±176.60ngL−1 (summer) in water samples. Obvious seasonal trends of PAH16 concentrations were found in the atmosphere and water. The values of PAH16 for both the atmosphere and the water were significantly correlated with temperature. (3) The monthly diffusive air–water exchange flux of total PAH16 ranged from −1.77×104ngm−2d−1 to 1.11×105ngm−2d−1, with an average value of 3.45×104ngm−2d−1. (4) The results of a Monte Carlo simulation showed that the monthly average PAH fluxes ranged from −3.4×103ngm−2d−1 to 1.6×104ngm−2d−1 throughout the year, and the uncertainties for individual PAHs were compared. (5) According to the sensitivity analysis, the concentrations of dissolved and gaseous phase PAHs were the two most important factors affecting the results of the flux calculations.

Characterization of polycyclic aromatic hydrocarbons in concurrently monitored surface seawater and sediment along Dalian coast after oil spill

Polycyclic aromatic hydrocarbons (PAHs) were measured in concurrently sampled surface seawater and sediment collected at 20 sites around Dalian, China 50 days after an oil spill accident. The concentrations of total PAHs ranged from 15 to 160ngL−1 in seawater, and from 64 to 2100ngg−1 dry weight in surface sediment. The spatial trends of PAHs in seawater, but not in sediment, showed a significant negative correlation with the distance from the oil spill site, indicating a strong source of PAHs from oil spill place to the surrounding seawater. The similar profiles for PAH composition in both crude oil and seawater could indicate that oil spill caused PAHs concentration in seawater, but not in sediment. Analysis of water–sediment exchange of PAHs showed that the direction of the net flux of PAHs was from sediment to seawater for most priority PAHs, and from water to sediment for a few HWM-PAHs.

Distribution, input pathway and soil–air exchange of polycyclic aromatic hydrocarbons in Banshan Industry Park, China

Given the steel industry park–city paired structure commonly found across China and it associated environmental pollution, the objective of this study was to examine the spatial–temporal distributions of polycyclic aromatic hydrocarbons (PAHs) as well as the relative contributions of the main influx pathways in Banshan steel industry park, China. We analyzed the concentrations of 16 PAHs in soil, air, water and dry/wet deposition samples using gas chromatography–mass spectrometry (GC–MS). The concentrations of ∑16-PAHs ranged from 572 to 4654μg/kg in April 2010; and the average concentration is 12.7% and 26.1% higher than that of April 2009 and April 2008, respectively, mainly due to the rapid increase of highly toxic high molecular weight (MW) PAHs. The principal input pathway for high and low MW PAHs was determined to be dry deposition (e.g., 69.73% for Benzo[a]pyrene) and wet deposition (e.g., 78.87% for Naphthalene), respectively. Together, 54.79% of total PAHs found in this region are via dry deposition, whereas wet deposition and river water irrigation contribute to 25.46% and 19.76% (corrected with toxic equivalency factors). The approach to the soil–air equilibrium was assessed by calculating fugacity quotients between soil and air samples, and the results indicate that the soil acted as a secondary source for light MW atmospheric PAHs and a sink for higher MW PAHs. It was also determined that the soil acted as a source for median MW PAHs, particularly PY.

Diffusive exchange of PAHs across the air–water interface of the Kaohsiung Harbor lagoon, Taiwan

Instantaneous air–water polycyclic aromatic hydrocarbons (PAHs) exchange fluxes were calculated in 22 pairs of ambient air and water samples from Kaohsiung Harbor lagoon, from December 2003 to January 2005. The highest net volatilization (3135 ng m−2 day−1) and absorptive (−1150 ng m−2 day−1) fluxes in the present study were obtained for the three-ring PAH phenanthrene on 7 April and 27 January 2004, respectively. All PAH diffusive fluxes for three-ring PAHs except phenanthrene were mainly volatilization exchange across the air–water interface. Phenanthrene and the four-ring PAHs were absorbed primarily from the atmosphere and deposited to the surface water, although some minor volatilization fluxes were also observed. Differences in flux magnitude and direction between the dry and wet seasons were also evident for PAHs. Strong absorptive/weaker volatilization PAH fluxes occurred in the dry season, but the opposite was found in the wet season. The mean daily PAH diffusive fluxes were an in flux of −635 ng m−2 day−1 in the dry season and an efflux of 686 ng m−2 day−1 in the wet season. The integrated absorbed and emitted fluxes of PAHs for harbor lagoon surface waters in the dry and wet seasons were 3.1 kg and 3.4 kg, respectively. Different from water bodies located in temperate zone, phenanthrene diffusive fluxes in Kaohsiung Harbor lagoon was favored in volatilization from surface waters during the wet season (April to September) because of scavenging by precipitation and dilution by prevailing southwesterly winds. In addition, this study used both of salinity and temperature to improve estimation of Henry's law constants (H) of PAHs in a tropical coastal area and show that correction for salinity produced 13–15% of differences in H values.

Study of air–soil exchange of polycyclic aromatic hydrocarbons (PAHs) in the north-central part of India – a semi arid region

Soil is the major environmental reservoir of organic compounds and soil-air exchange is a key process in governing the environmental fate of these compounds on a regional and global scale. Samples of air and soil were collected to study the levels of PAHs in the air and soil of the Agra region. Concentrations of PAH measured at four locations in the city of Agra, covers industrial, residential, roadside and agricultural areas. Samples were extracted with hexane by ultrasonic agitation. Extracts were then fractioned on a silica-gel column and the aromatic fraction was analysed by GC-MS. The mean concentration of the total PAH (T-PAH) in the air of Agra was 24.95, 17.95 and 14.25 ng m(-3), during winter, monsoon and summer respectively. The average concentration of T-PAH in the soil of Agra was 12.50, 8.25 and 6.44 μg g(-1) in winter, monsoon and summer seasons respectively. The aim of this study was to investigate the rate of approach to equilibrium partitioning of PAHs between air and soil compartments and to determine the direction of net flux of the studied PAH between air and soil. Calculated soil-air fugacity quotients indicate that the soil may now be a source of some lighter weight PAHs to the atmosphere, whereas it appears to be still acting as a long-term sink for the heavier weight PAHs to some extent in this region.

Atmospheric concentrations and air–soil gas exchange of polycyclic aromatic hydrocarbons (PAHs) in remote, rural village and urban areas of Beijing–Tianjin region, North China

Forty passive air samplers were deployed to study the occurrence of gas and particulate phase PAHs in remote, rural village and urban areas of Beijing–Tianjin region, North China for four seasons (spring, summer, fall and winter) from 2007 to 2008. The influence of emissions on the spatial distribution pattern of air PAH concentrations was addressed. In addition, the air–soil gas exchange of PAHs was studied using fugacity calculations. The median gaseous and particulate phase PAH concentrations were 222 ng/m 3 and 114 ng/m 3, respectively, with a median total PAH concentration of 349 ng/m 3. Higher PAH concentrations were measured in winter than in other seasons. Air PAH concentrations measured at the rural villages and urban sites in the northern mountain region were significantly lower than those measured at sites in the southern plain during all seasons. However, there was no significant difference in PAH concentrations between the rural villages and urban sites in the northern and southern areas. This urban–rural PAH distribution pattern was related to the location of PAH emission sources and the population distribution. The location of PAH emission sources explained 56%–77% of the spatial variation in ambient air PAH concentrations. The annual median air–soil gas exchange flux of PAHs was 42.2 ng/m 2/day from soil to air. Among the 15 PAHs measured, acenaphthylene (ACY) and acenaphthene (ACE) contributed to more than half of the total exchange flux. Furthermore, the air–soil gas exchange fluxes of PAHs at the urban sites were higher than those at the remote and rural sites. In summer, more gaseous PAHs volatilized from soil to air because of higher temperatures and increased rainfall. However, in winter, more gaseous PAHs deposited from air to soil due to higher PAH emissions and lower temperatures. The soil TOC concentration had no significant influence on the air–soil gas exchange of PAHs.

Modeling the atmospheric transport and outflow of polycyclic aromatic hydrocarbons emitted from China

An Euler atmospheric transport model CanMETOP (Canadian Model for Environmental Transport of Organochlorine Pesticides) was applied to the atmospheric transport and outflow of polycyclic aromatic hydrocarbons (PAHs) in China in 2003 based on a square kilometer resolution emission inventory. The reaction with OH radical, gas/particle partition by considering the adsorption onto total aerosol surface area, and dynamic soil/ocean–air exchange of PAHs were also considered. The results show that the spatial distribution of PAH concentration levels in the atmosphere is greatly controlled by emission and meteorological conditions. Elevated concentration levels are predicted in Shanxi, Guizhou, North China Plain, Sichuan Basin and Chongqing metropolitan areas due to the high emission densities at those locations. High concentrations are also modeled in environments offshore of China and in the western Pacific Ocean. The model also predicts a slightly decreasing vertical profile in the planetary boundary layer (lower than ∼1 km), but concentration decreases ∼2 orders of magnitude in the free atmosphere. The Westerlies as well as the East Asian Monsoon and local topographical forcings are identified as key factors influencing the transport pattern of PAHs in China. In 2003, ∼3800°tons of the sixteen parent PAHs listed on USEPA priority control list were transported out of China with about 80% transported through the eastern boundary. The outflow concentrates near 30°N, signifying a slight discrepancy from the position of emission density peaks. The center of the outflow plume is located at a height of ∼1 km at 120°E, and climbs to 3.5 km and 5 km at 130°E and 140°E, respectively. A seasonal variation of 5–6 fold is also found for the outflow flux with greatly elevated transport flux in spring and winter. ► Use a state-of-the-art Euler numerical model to study the transport of PAHs. ► The total outflow flux of PAHs was estimated to be 3800 tons per year. ► The high spatial resolution revealed transport patterns at smaller scales.

Particle-phase dry deposition and air–soil gas exchange of polycyclic aromatic hydrocarbons (PAHs) in Izmir, Turkey

Ambient air and dry deposition samples were collected at suburban and urban sites in Izmir, Turkey. Atmospheric total (particle+gas) ∑14PAHs concentrations were 36±39 and 144±163ngm−3 for suburban and urban sites, respectively. Phenanthrene was the most abundant compound at all sites, and all samples were dominated by low molecular weight PAHs. Average particulate ∑14PAH dry deposition fluxes were 8160±5024 and 4286±2782ngm−2 day−1 and overall average particulate dry deposition velocities were 1.5±2.4 and 1.0±2.3cms−1 for suburban and urban sites, respectively. Soil samples were collected at suburban site. Average soil concentration for ∑14PAH was 55.9±14.4ngg−1 dry weight. Calculated gas-phase air–soil exchange fluxes indicated that fluorene, phenanthrene, anthracene, and carbazole were deposited to soil in winter while they were volatilized in summer. Other compounds (fluoranthene-benzo[g,h,i]perylene) were deposited to soil in both periods. Annual average fluxes of PAHs representing soil to air (i.e., gas volatilization) and air to soil transfer (i.e., gas absorption, dry deposition, and wet deposition) processes were also compared. All processes were comparable for Σ14PAHs however their input was dominated by gas absorption. Gas absorption dominated for lower molecular weight PAHs, however dry deposition dominated for higher molecular weight PAHs. The results have suggested that for fluorene, soil and air may be approaching a steady state condition. For the remaining compounds, there was a net accumulation into the soil.

Exchange of polycyclic aromatic hydrocarbons among the atmosphere, water, and sediment in coastal embayments of southern California, USA

The present study investigated cross-media transport between both the sediment and the water column and between the water column and the atmosphere, to understand the role of each compartment as a source or a sink of polycyclic aromatic hydrocarbons (PAH) in southern California, USA, coastal waters. Concentrations of PAH were measured in the atmosphere, water column, and sediment at four water-quality-impaired sites in southern California: Ballona Creek Estuary, Los Angeles Harbor, Upper Newport Bay, and San Diego Bay. These concentrations were used to calculate site-specific sediment-water and atmosphere-water exchange fluxes. The net sediment-water exchange of total PAH (t-PAH) was positive, indicating that sediments were a source to the overlying water column. Furthermore, the net atmosphere-water exchange (gas exchange + dry particle deposition) of t-PAH was typically positive also, indicating the water column was a net source of PAH to the surrounding atmosphere through gas exchange. However, in all cases, the magnitude of the diffusive flux of PAH out of the sediments and into the water column far exceeded input or output of PAH through air/water exchange processes. These results demonstrate the potential importance of contaminated sediments as a source of PAH to the water column in coastal waters of southern California.

Atmospheric concentrations, dry deposition and air–soil exchange of polycyclic aromatic hydrocarbons (PAHs) in an industrial region in Turkey

Concurrent ambient air and dry deposition samples were collected during two sampling periods at the Aliaga industrial region in Izmir, Turkey. ∑ 15-PAH (particulate + gas) concentrations ranged between 7.3 and 44.8 ng m −3 (average ± S.D., 25.2 ± 8.8 ng m −3) and 10.2–71.9 ng m −3 (44.1 ± 16.6 ng m −3) in summer and winter, respectively. Winter/summer individual ambient PAH concentration ratios ranged between 0.8 (acenaphthene) and 6.6 (benz[ a]anthracene) indicating that wintertime concentrations were affected by residential heating emissions. In contrast to the ambient concentrations, ∑ 15-PAH particle dry deposition fluxes were higher in summer (5792 ± 3516 ng m −2 day −1, average ± S.D.) than in winter (2650 ± 1829 ng m −2 day −1), probably due to large particles from enhanced re-suspension of polluted soil particles and road dust. Average overall dry deposition velocity of PAHs calculated using the dry deposition fluxes and particle-phase concentrations was 2.9 ± 3.5 cm s −1. ∑ 15-PAH concentrations in soils taken from 50 points in the area ranged between 11 and 4628 μg kg −1 in dry weight. The spatial distribution of these concentrations indicated that the urban Aliaga, steel plants, the petroleum refinery, and the petrochemical plant are the major Σ 15-PAH sources in the area. Fugacity calculations in air and soil showed that the soil acts as a secondary source to the atmosphere for low molecular weight PAHs in summer and as a sink for the higher molecular weight ones in summer and winter.

Exchange of polycyclic aromatic hydrocarbons across the air–water interface at the creek adjoining Mumbai harbour, India

Concentration levels of polycyclic aromatic hydrocarbons (PAHs) have been determined in air and water in order to estimate the magnitude and direction of gas flux across the air–water interface at the creek adjoining the Mumbai harbour, India. The range of total PAHs was found to be 4.1–30.4 ng/m3 in air and 84.3–377.5 ng/l in seawater, respectively. The lower molecular weight PAHs revealed positive values of the fluxes indicating the tendency for transfer of these contaminants from water to air. In contrast, fluxes of less volatile compounds like benzo(k)fluoranthene and benzo(a)pyrene were always from the atmosphere into the surface water of the creek at all locations and sampling periods. While the fugacity ratio ranged from 0.12 to 6.97, it was found greater than 1 for the lower molecular weight PAHs and less than 1 for higher molecular weight PAHs. The present study suggests the active transfer of lower molecular weight dissolved PAHs into the atmosphere due to volatilization and deposition of higher molecular weight gas-phase PAHs into the surface water.

Mass transfer coefficients for polycyclic aromatic hydrocarbons (PAHs) to the water surface sampler:: comparison to modeled results

A sampling program was conducted between June and October 1995 in Chicago, IL using a modified water surface sampler (WSS) and dry deposition plates to measure the particulate dry deposition and gas exchange of PAHs. Oxygen transfer experiments were also conducted to evaluate the collection properties of the WSS for gas-phase compounds. Gas-phase fluxes were determined by subtracting the dry deposition plate fluxes (particulate) from WSS fluxes (particulate+gas). These fluxes were divided by concurrently measured ambient concentrations to obtain overall gas phase mass transfer coefficients. Two different two-film models, one developed based on experiments performed with the WSS and, one previously published, were compared to these results. Experimentally determined average gas phase overall mass transfer coefficient ( K g) for seven PAHs was 0.74±0.52 cm s −1. Experimental K g values agreed well with those predicted by the model developed for WSS. The values predicted by previously proposed models were within a factor of 3 of the experimental ones.

Diffusive Exchange of Polycyclic Aromatic Hydrocarbons across the Air−Water Interface of the Patapsco River, an Urbanized Subestuary of the Chesapeake Bay

Air−water exchange fluxes of 13 polycyclic aromatic hydrocarbons (PAHs) were determined along a transect in the Patapsco River from the Inner Harbor of Baltimore, MD, to the mainstem of the northern Chesapeake Bay. Sampling took place at six sites during three sampling intensives (June 1996, February 1997, and July 1997) and at one site every ninth day between March 1997 and March 1998 to measure spatial, daily, and annual variability in the fluxes. The direction and magnitude of the daily fluxes of individual PAHs were strongly influenced by the wind speed and direction, by the air temperature, and by the highly variable PAH concentrations in the gas and dissolved phases. Individual fluxes ranged from 14 200 ng m-2 day-1 net volatilization of fluorene during high winds to 11 400 ng m-2 day-1 net absorption of phenanthrene when prevailing winds blowing from the northwest across the city of Baltimore elevated gaseous PAH concentrations over the water. The largest PAH volatilization fluxes occurred adjacent...

Polycyclic aromatic hydrocarbons (PAHs) in Chicago air

Ambient air samples were collected in Chicago, IL between June and October 1995 as part of a study to investigate the dry deposition and air–water exchange of polycyclic aromatic hydrocarbons (PAHs). A modified high-volume sampler (PS-1 sampler) was used to collect airborne PAHs in both the particulate and gas phases. The average total (gas+particulate) Σ 14-PAH concentration was 428±240 ng m −3, similar to those previously observed in Chicago, IL and other urban areas. The particle/gas phase distribution varied widely. The gas phase percentage ranged from 1.1 to 99.4%, and generally decreased with increasing molecular weight. The amount of PAHs associated with the particulate phase increased with decreasing temperature, probably due to the temperature dependence of gas/particle partitioning. Concentrations of PAHs with molecular weights between 154 and 202 were correlated well with phenanthrene concentrations while compounds with molecular weights higher than 202 had little or no correlation with phenanthrene concentration, probably due to the different partitioning, transport and removal characteristics of low and high molecular weight compounds.

Measurement of Dry Deposition and Air−Water Exchange of Polycyclic Aromatic Hydrocarbons with the Water Surface Sampler

Recent work has shown that dry deposition and gas exchange of semivolatile organic compounds in the Great Lakes is important. However, there is no generally accepted method for collecting particulate dry deposition or gas exchange. In this work the Water Surface Sampler (WSS) was modified and used in combination with dry deposition plates to measure the particulate dry deposition and gas exchange of PAHs. Simultaneous dry deposition and ambient air samples were collected between June and October 1995 in Chicago, IL. Total (particulate + gas) fluxes were measured with the WSS, while particulate fluxes were measured with dry deposition plates. Average Σ14-PAH and particulate Σ14-PAH fluxes were 360 ± 146 μg/m2 d and 144 ± 60 μg/m2 d, respectively. Gas-phase fluxes, determined by subtracting the dry deposition plate fluxes (particulate) from WSS fluxes (particulate + gas), averaged 170 ± 72 μg/m2 d. The measured particulate dry deposition and gas exchange fluxes were substantially higher than those previousl...

Gaseous Exchange of Polycyclic Aromatic Hydrocarbons across the Air−Water Interface of Southern Chesapeake Bay

The gas exchange fluxes of polycyclic aromatic hydrocarbons (PAHs) across the air−water interface of southern Chesapeake Bay were calculated using a modified two-film exchange model. Sampling covered the period January 1994−June 1995 for five sites on the southern Chesapeake Bay ranging from rural to urban and highly industrialized. Simultaneous air and water samples were collected, and the atmospheric gas phase and surface water dissolved phase analyzed via GC/MS for 17 PAHs. The instantaneous gas flux was calculated for each compound using Henry's law constants, diffusivities, and hydrological and meteorological parameters. The direction and magnitude of gas transfer were found to be controlled by water temperature and gas-phase concentrations. Fluxes were determined to vary in direction and magnitude both spatially and temporally across the air−water interface of southern Chesapeake Bay. The range of gas exchange is of the same order as atmospheric wet and dry depositional fluxes to southern Chesapeake Bay. The results of this study support the hypothesis that gas exchange is a major transport process affecting concentrations and exposure levels of PAHs in southern Chesapeake Bay.

Specificity in the homogeneous metal-catalysed isotopic hydrogen exchange of polycyclic aromatic hydrocarbons. Evidence for complex formation between aromatic hydrocarbons and transition metals

Specificity in the homogeneous metal-catalysed isotopic hydrogen exchange of polycyclic aromatic hydrocarbons. Evidence for complex formation between aromatic hydrocarbons and transition metals