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.     

Atmospheric distribution of polycyclic aromatic hydrocarbons and deposition to Galveston Bay,Texas, USA

Estimates of the atmospheric deposition to Galveston Bay of polycyclic aromatic hydrocarbons (PAHs) are made using precipitation and meteorological data that were collected continuously from 2 February 1995 to 6 August 1996 at Seabrook, TX, USA. Particulate and vapor phase PAHs in ambient air and particulate and dissolved phases in rain samples were collected and analyzed. More than 95% of atmospheric PAHs were in the vapor phase and about 73% of PAHs in the rain were in the dissolved phase. Phenanthrene and napthalene were the dominant compounds in air vapor and rain dissolved phases, respectively, while 5 and 6 ring PAH were predominant in the particulate phase of both air and rain samples. Total PAH concentrations ranged from 4 to 161 ng m⁻³ in air samples and from 50 to 312 ng l⁻¹ in rain samples. Temporal variability in total PAH air concentrations were observed, with lower concentrations in the spring and fall (4–34 ng m ⁻³) compared to the summer and winter (37–161 ng m⁻³). PAHs in the air near Galveston Bay are derived from both combustion and petroleum vaporization. Gas exchange from the atmosphere to the surface water is estimated to be the major deposition process for PAHs (1211 μg m^{− 2} yr^{− 1}), relative to wet deposition (130 μg m⁻² yr^{− 1}) and dry deposition (99 μg m⁻² yr^{− 1}). Annual deposition of PAHs directly to Galveston Bay from the atmosphere is estimated as 2  t yr⁻¹.     

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.     

Influence of the surface microlayer on atmospheric deposition of aerosols and polycyclic aromatic hydrocarbons

Atmospheric dry deposition is an important process for the introduction of aerosols and pollutants to aquatic environments. The objective of this paper is to assess, for the first time, the influence that the aquatic surface microlayer plays as a modifying factor of the magnitude of dry aerosol deposition fluxes. The occurrence of a low surface tension (ST) or a hydrophobic surface microlayer has been generated by spiking milli-Q water or pre-filtered seawater with a surfactant or octanol, respectively. The results show that fine mode (<2.7 μm) aerosol phase PAHs deposit with fluxes 2–3 fold higher when there is a low ST aquatic surface due to enhanced sequestration of colliding particles at the surface. Conversely, for PAHs bound to coarse mode aerosols (>2.7 μm), even though there is an enhanced deposition due to the surface microlayer for some sampling periods, the effect is not observed consistently. This is due to the importance of gravitational settling for large aerosols, rendering a lower influence of the aquatic surface on dry deposition fluxes. ST (mN m⁻¹) is identified as one of the key factor driving the magnitude of PAH dry deposition fluxes (ng m⁻² d⁻¹) by its influence on PAH concentrations in deposited aerosols and deposition velocities (v_d, cm s⁻¹). Indeed, v_d values are a function of ST as obtained by least square fitting and given by Ln(v_d)=−1.77 Ln(ST)+5.74 (r²=0.95) under low wind speed (average 4 m s⁻¹) conditions.     

Atmospheric deposition of organochlorine contaminants to Galveston Bay,Texas

Atmospheric monitoring of PCBs and chlorinated pesticides (e.g., HCHs, chlordanes, and DDTs) in Galveston Bay was conducted at Seabrook, Texas. Air and wet deposition samples were collected from 2 February 1995 and continued through 6 August 1996. Vapor total PCB (tPCB) concentrations in air ranged from 0.21 to 4.78 ng m⁻³ with a dominance of tri-chlorinated PCBs. Dissolved tPCBs in rain ranged from 0.08 to 3.34 ng l⁻¹, with tetra-chlorinated PCBs predominating. The predominant isomers found in air and rain were α- and γ-HCH, α- and γ-chlordanes, 4,4′-DDT, and dieldrin. The concentrations of PCBs and pesticides in the air and rain revealed no clear seasonal trend. Elevated levels of PCBs in the air occurred when temperatures were high and wind came from urban and industrialized areas (S, SW, NW, and W of the site). Concentrations of HCHs were elevated in April, May, and October, perhaps due to local and/or regional applications of γ-HCH (lindane). Other pesticides showed no notable temporal variation. When winds originated from the Gulf of Mexico (southeasterly), lower concentrations of organochlorines were detected in the air. The direct deposition rate (wet+dry) of PCBs to Galveston Bay (6.40 μg m⁻² yr⁻¹) was significantly higher than that of pesticides by a factor of 5–10. The net flux from gas exchange estimated for PCBs was from Galveston Bay water to the atmosphere (78 μg m⁻² yr⁻¹). Gas exchange of PCBs from bay water to the atmosphere was the dominant flux.     

Mercury deposition through litterfall in an Atlantic Forest at Ilha Grande,Southeast Brazil

Atmospheric Hg transfer to the forest soil through litterfall was investigated in a primary rainforest at Ilha Grande (Southeast Brazil) from January to December 1997. Litter mass deposition reached 10.0 t ha⁻¹ y⁻¹, with leaves composing 50–84% of the total litter mass. Concentrations of Hg in the total fallen litter varied from 20 to 244 ng g⁻¹, with higher concentrations during the dry season, between June and August (225 ± 17 ng g⁻¹), and lower concentrations during the rainy season (99 ± 54 ng g⁻¹). This seasonal variability was reflected in the Hg flux through litterfall, which corresponded to a Hg input to the forest floor of 122 μg m⁻² y⁻¹, with average Hg deposition of 16.5 ± 1.5 μg m⁻² month⁻¹ during and just after the dry season (June–September) and 7.0 ± 3.6 μg m⁻² month⁻¹ in the rest of the year. The variability in meteorological conditions (determining atmospheric Hg availability to foliar scavenging) may explain the pulsed pattern of Hg deposition, since litterfall temporal variability was generally unrelated with such deposition, except by a peak in litterfall production in September. Comparisons with regional data on Hg atmospheric deposition show that litterfall promotes Hg deposition at Ilha Grande two to three orders of magnitude higher than open rainfall deposition in non-industrialized areas and approximately two times higher than open rainfall deposition in industrialized areas in Rio de Janeiro State. The observed input suggests that atmospheric Hg transfer through litterfall may explain a larger fraction of the total Hg input to forest soils in Southeast Brazil than those recorded at higher latitudes.     

Conditional sampling for measuring mercury vapor fluxes

Surface–atmosphere mercury fluxes are difficult to measure accurately. Current techniques include dynamic flux chambers and micrometeorological gradient and aerodynamic approaches, all of which have a number of intrinsic problems associated with them. We have adapted conditional sampling (relaxed eddy accumulation), a micrometeorological technique commonly used to measure other trace gas fluxes, to measure surface–air mercury fluxes. Our initial flux measurement campaign over an agricultural soil consisted of two 1-week measurement periods, and was longer in duration than previously reported mercury flux measurement periods. Fluxes during both measurement periods ranged between 190.5 (evolution) and –91.7 ng m⁻² h⁻¹ (deposition) with an average evolution of 9.67 ng m⁻² h⁻¹. The data showed significant diurnal trends, weakly correlated with shallow soil temperatures and solar radiation. This initial trial run indicates that conditional sampling has much promise for the accurate quantification of both short and long-term mercury fluxes.     

Dry deposition of ammonia,nitric acid,ammonium, and nitrate to alpine tundra at Niwot Ridge,Colorado

Micrometeorological measurements and ambient air samples, analyzed for concentrations of NH₃, HNO₃, NH₄⁺, and NO₃⁻, were collected at an alpine tundra site on Niwot Ridge, Colorado. The measured concentrations were extremely low and ranged between 5 and 70 ng N m⁻³. Dry deposition fluxes of these atmospheric species were calculated using the micrometeorological gradient method. The calculated mean flux for NH₃ indicates a net deposition to the surface and indicates that NH₃ contributed significantly to the total N deposition to the tundra during the August–September measurement period. Our pre-measurement estimate of the compensation point for NH₃ in air above the tundra was 100–200 ng N m⁻³; thus, a net emission of NH₃ was expected given the low ambient concentrations of NH₃ observed. Based on our results, however, the NH₃ compensation point at this alpine tundra site appears to have been at or below about 20 ng N m⁻³. Large deposition velocities (>2 cm s⁻¹) were determined for nitrate and ammonium and may result from reactions with surface-derived aerosols.     

Dry deposition and foliar leaching of mercury and selected trace elements in deciduous forest throughfall

The estimated annual throughfall deposition flux of Hg in a northern mixed-hardwood forest in the Lake Huron Watershed was 10.5±1.0 μg m⁻² compared to an annual precipitation Hg flux of 8.7±0.5 μg m⁻² (June 1996–June 1997). The source of this additional Hg in throughfall is often attributed to wash-off of dry deposition, but foliar leaching of Hg may also be important. To determine the influence of both dry deposition and foliar leaching of Hg and other elements in throughfall, we measured a suite of trace elements (Hg, Al, Mg, V, Mn, Cu, Zn, As, Rb, Sr, Cd, Ba, La, Ce, and Pb) in throughfall, precipitation, and ambient air samples from a northern mixed-hardwood forest. Based on a multiple linear regression model, dry deposition had the most important influence on Hg, Al, La, Ce, V, As, Cu, Zn, Cd, and Pb fluxes while foliar leaching strongly influenced Mg, Mn, Rb, Sr, and Ba fluxes in net throughfall. The Hg dry deposition flux was estimated using gaseous and aerosol Hg measurements and modeled deposition velocities. The calculated dry deposition flux (∼12–14 μg m⁻²) of Hg to the canopy indicated that atmospheric deposition of Hg could easily account for all of the Hg deposited in net throughfall (1.9±0.1 μg m⁻²). Although there is a large uncertainty associated with these techniques, the modeling estimates indicate that atmospheric Hg may account for all of the Hg deposited in litterfall (11.4±2.8 μg m⁻²).     

Characteristics of mercury exchange flux between soil and air in the heavily air-polluted area,eastern Guizhou,China

To investigate the characteristics of mercury exchange between soil and air in the heavily air-polluted area, total gaseous mercury (TGM) concentration in air and Hg exchange flux were measured in Wanshan Hg mining area (WMMA) in November, 2002 and July–August, 2004. The results showed that the average TGM concentrations in the ambient air (17.8–1101.8 ng m⁻³), average Hg emission flux (162–27827 ng m⁻² h⁻¹) and average Hg dry deposition flux (0–9434 ng m⁻² h⁻¹) in WMMA were 1–4 orders of magnitude higher than those in the background area. It is said that mercury-enriched soil is a significant Hg source of the atmosphere in WMMA. It was also found that widely distributed roasted cinnabar banks are net Hg sources of the atmosphere in WMMA. Relationships between mercury exchange flux and environmental parameters were investigated. The results indicated that the rate of mercury emission from soil could be accelerated by high total soil mercury concentration and solar irradiation. Whereas, highly elevated TGM concentrations in the ambient air can restrain Hg emission from soil and even lead to strongly atmospheric Hg deposition to soil surface. A great amount of gaseous mercury in the heavily polluted atmosphere may cycle between soil and air quickly and locally. Vegetation can inhibit mercury emission from soil and are important sinks of atmospheric mercury in heavily air-polluted area.     

Sources of sodium in atmospheric fine particles

Concentrations of size fractionated particulate sodium and potassium were measured in both marine and urban air. Marine air sampling was conducted during a cruise on R/V Hakuho-maru in the northwestern North Pacific in the summer of 1998. Urban air sampling was performed in the central part of Tokyo in 1997 and 1998. The fine sodium concentration (D<1.1 μm) in “Urban” air (180 ng m⁻³) was 3 times higher than that in “Marine” air (56 ng m⁻³). In the urban air samples, the size distributions of sodium and potassium showed bimodal peaks in the fine particle range (D<1.1 μm) and in the coarse particle range (D>1.1 μm). The existence of anthropogenic sodium in the fine particle range was detected in the urban air. The K/Na weight ratios in the fine particle range of the urban air (1.8–2.7) was 50–75 times higher than that in seawater (0.036). Potassium in the urban air is thought to be derived largely from anthropogenic sources. In the urban air samples, a high correlation between fine sodium and fine potassium concentrations suggests that they have the same anthropogenic source. Reevaluating the K/Na ratios in marine air to be relatively higher than that in seawater, we can estimate that several percents of anthropogenic sodium can be transported from land to remote marine air.     

High volume electrostatic field-sampler for collection of fine particle bulk samples

A high volume electrostatic field-sampler was developed for collection of fine particles, which easily can be recovered for subsequent sample characterisation and bioassays. The sampler was based on a commercial office air cleaner and consisted of a prefilter followed by electrostatic collection plates operating at 2.7 kV. The sampler performance was characterised for 26 nm to 5.4 μm-size particles in urban street air. The collection efficiency reached a maximum (60–70%) between 0.2 and 0.8 μm and dropped to ∼25% at 30 nm and 2.5 μm, respectively. After extraction in water, the particle loss was<2%. The extraction efficiency for dry lyophilised particulate matter was above 80%, allowing retrievement of ∼12 mg day⁻¹ in urban street air at PM₁₀ levels of ∼24 μg m⁻³. The ozone generating capacity of the corona discharge during operation was on the order of 10 ppb. A polycyclic aromatic hydrocarbons (PAH) degradation test using benzo[a]pyrene as a model showed that ∼85% was degraded after 24 h. However, similar results were observed when the corona discharge was switched off. Hence, the ozone and other corona discharge reactants do not appear to contribute considerably to PAH-degradation. The overall results show that the sampler type is a promising alternative to traditional sampling of fine particles for bulk analysis and bioassays. The main advantages are simple operation, high stability, high quantifiable particle recovery rates and low cost.     

Estimates of air-sea exchange of mercury in the Baltic Sea

The concentrations of total gaseous mercury (TGM) in air over the southern Baltic Sea and dissolved gaseous mercury (DGM) in the surface seawater were measured during summer and winter. The summer expedition was performed on 02–15 July 1997, and the winter expedition on 02–15 March 1998. Average TGM and DGM values obtained were 1.70 and 17.6 ng m⁻³ in the summer and 1.39 and 17.4 ng m⁻³ in the winter, respectively. Based on the TGM and DGM data, surface water saturation and air-water fluxes were calculated. The results indicate that the seawater was supersaturated with gaseous mercury during both seasons, with the highest values occurring in the summer. Flux estimates were made using the thin film gas-exchange model. The average Hg fluxes obtained for the summer and winter measurements were 38 and 20 ng m⁻² d⁻¹, respectively. The annual mercury flux from this area was estimated by a combination of the TGM and DGM data with monthly average water temperatures and wind velocities, resulting in an annual flux of 9.5 μg m⁻² yr⁻¹. This flux is of the same order of magnitude as the average wet deposition input of mercury in this area. This indicates that reemissions from the water surface need to be considered when making mass-balance estimates of mercury in the Baltic Sea as well as modelling calculations of long-range transboundary transport of mercury in northern Europe.     

Atmospheric deposition of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in Guangzhou,China

Atmospheric deposition of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) was investigated at four locations, namely at Yuancun, Wushan, Haizhu and Changban in Guangzhou City, Guangdong Province. The annual deposition fluxes of tetra- to octa-CDD/Fs (total PCDD/Fs) were found to range from 170 to 3000 (mean 1500) pg m⁻² day⁻¹, and the fluxes of total 2, 3, 7, 8-substituted PCDD/F congeners ranged from 2.1 to 41 (mean 20) pg WHO-TEQ m⁻² day⁻¹ at Wushan. The average deposition fluxes of total 2, 3, 7, 8-substituted PCDD/F congeners in rainy season were found to be 37, 27 and 28 pg WHO-TEQ m⁻² day⁻¹ at Yuancun, Haizhu and Changban, respectively, and the PCDD/F deposition fluxes behaved obviously higher in rainy season than in dry season. Results from regression analysis showed that number of rainy days, the amount of wet precipitation, PCDD/F concentrations in particles and organic carbon content played important roles in the variation of PCDD/F deposition fluxes. Monthly average temperatures change little over the year. Therefore, it only played a minor role in monthly variation of PCDD/F deposition fluxes. Particle deposition fluxes were generally not considered as the factor that could cause the differences in PCDD/F deposition fluxes between rainy and dry season, but were found to be related with PCDD/F deposition fluxes in rainy season or dry season. It was found that the profiles of PCDD/F homologs or congeners in the samples were the same either spatially or temporally, indicating that the PCDD/F emission sources were similar to one another. The similarities in PCDD/F homolog patterns and the differences in deposition fluxes between samples collected from heavy-traffic roadside and nearby residence house roof indicated that vehicle exhaust might be an important source for PCDD/F in Guangzhou. PCDD/F concentrations and profiles of PCDD/F homologs in atmospheric deposition were compared with those in both total suspended particles in air and soils, and conclusions indicated that atmospheric deposition possibly tended to remove lower-chlorinated DD/Fs from air and was one of sources for PCDD/Fs in soils.     

Measurements of GEM fluxes and atmospheric mercury concentrations (GEM,RGM and Hgp) from an agricultural field amended with biosolids in Southern Ont., Canada (October 2004–November 2004)

Five weeks of gaseous elemental mercury (GEM), reactive gaseous mercury (RGM) and particle bound mercury (Hg^p) concentrations as well as fluxes of GEM were measured at Maryhill, Ontario, Canada above a biosolids amended field. The study occurred during the autumn of 2004 (October–November) to capture the effects of cool weather conditions on the behaviour of mercury in the atmosphere. The initial concentration of total mercury (Hg) in the amended soil was relatively low (0.4 μg g⁻¹±10%).A micrometeorological approach was used to infer the flux of GEM using a continuous two-level sampling system with inlets at 0.40 and 1.25 m above the soil surface to measure the GEM concentration gradient. The required turbulent transfer coefficients were derived from meteorological parameters measured on site. The average GEM flux over the study was 0.1±0.2 ng m⁻² h⁻¹(±one standard deviation). The highest averaged hourly GEM fluxes occurred when the averaged net radiation was highest, although the slight diurnal patterns observed were not statistically significant for the complete flux data series. GEM emission fluxes responded to various local events including the passage of a cold front when the flux increased to 2 ng m⁻² h⁻¹ and during a biosolids application event at an adjacent field when depositional fluxes peaked at −3 ng m⁻² h⁻¹. Three substantial rain events during the study kept the surface soil moisture near field capacity and only slightly increased the GEM flux. Average concentrations of RGM (2.3±3.0 pg m⁻³), Hg^p (3.0±6.2 pg m⁻³) and GEM (1.8±0.2 ng m⁻³) remained relatively constant throughout the study except when specific local events resulted in elevated concentrations. The application of biosolids to an adjacent field produced large increases in Hg^p (25.8 pg m⁻³) and RGM (21.7 pg m⁻³) concentrations only when the wind aligned to impact the experimental equipment. Harvest events (corn) in adjacent fields also corresponded to higher concentrations of GEM and Hg^p but with no elevated peaks in RGM concentrations. Diurnal patterns were not statistically significant for RGM and Hg^p at Maryhill.     

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.     

The composition and sources of PM2.5 organic aerosol in two urban areas of Chile

Fine particle (PM_2.5) samples were collected, using a charcoal diffusion denuder, in two urban areas of Chile, Santiago and Temuco, during the winter and spring season of 1998. Molecular markers of the organic aerosol were determined using GC/MS. Diagnostic ratios and molecular tracers were used to investigate the origin of carbonaceous aerosols. As main sources, road and non-road engine emissions in Santiago, and wood burning in Temuco were identified. Cluster analysis was used to compare the chemical characteristics of carbonaceous aerosols between the two urban environments. Distinct differences between Santiago and Temuco samples were observed. High concentrations of isoprenoid (30–69 ng m⁻³) and unresolved complex mixture (UCM) of hydrocarbons (839–1369 ng m⁻³) were found in Santiago. High concentrations of polynuclear aromatic hydrocarbons (751±304 ng m⁻³) and their oxygenated derivatives (4±2 ng m⁻³), and of n-alk-1-enes (16±13 ng m⁻³) were observed in Temuco.     

Air–water exchange fluxes of polycyclic aromatic hydrocarbons in the tropical coast,Taiwan

Air–water exchange fluxes of polycyclic aromatic hydrocarbons (PAHs) were simultaneously measured in air and water samples from two sites on the Kenting coast, located at the southern tip of Taiwan, from January to December 2010. There was no significant difference in the total PAH (t-PAH) concentrations in both gas and dissolved phases between these two sites due to the less local input which also coincided to the low levels of t-PAH concentration; the gas and dissolved phases averaged 1.29 ± 0.59 ng m^?3 and 2.17 ± 1.19 ng L^?1 respectively. The direction and magnitude of the daily flux of PAHs were significantly influenced by wind speed and dissolved PAH concentrations. Individual PAH flux ranged from 627 ng m^?2 d^?1 volatilization of phenanthrene during the rainy season with storm–water discharges raising dissolved phase concentration, to 67 ng m^?2 d^?1 absorption of fluoranthene during high wind speed periods. Due to PAH annual fluxes through air–water exchange, Kenting seawater is a source of low molecular weight PAHs and a reservoir of high molecular weight PAHs. Estimated annual volatilization fluxes ranged from 7.3 μg m^?2 yr^?1 for pyrene to 50 μg m^?2 yr^?1 for phenanthrene and the absorption fluxes ranged from ?2.6 μg m^?2 yr^?1 for chrysene to ?3.5 μg m^?2 yr^?1 for fluoranthene.     

Atmospheric bulk deposition of dioxin and furans to Danish background areas

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) were measured in bulk deposition at three Danish rural forest sites with a mutual maximum distance of 450 km. At one of the forest sites concentrations in the ambient atmosphere were sampled from a 12 m high tower. Sampling was carried out within a period of 3 years with sampling intervals of 1–2 months. Mean bulk deposition fluxes were 1 ng m⁻² yr⁻¹ I-TEQ and deviated less than 30% between the sites. Yearly average PCDD/F concentrations in the atmosphere were 24 fg m⁻³ I-TEQ with maximum values in the winter period. During winter months atmospheric concentrations of PCDD/F and oxidized sulphur compounds showed a positive correlation, furthermore seasonal bulk deposition showed correlation between PCDD/F and sulphate.     

Denuder measurements of gas and aerosol species above Arctic snow surfaces at Alert 2000

Gas and aerosol measurements were made during the Polar Sunrise Experiment 2000 at Alert, Nunavut (Canada), using two independent denuder/filter systems for sampling and subsequent analysis by ion chromatography. Twelve to forty-eight hour samples were taken during a winter (9–21 February 2000) and a spring (17 April–5 May 2000) campaign. During the spring campaign, samples were taken at two different heights above the snow surface to investigate concentration differences. Total particulate NO₃⁻ is the most abundant inorganic nitrogen compound during Arctic springtime (mean 137.4 ng m⁻³). The NO₃⁻ fluxes were calculated above the snow surface to help identify processes that control snow–atmosphere exchange of reactive nitrogen compounds. We suggest that the observed fluxes of coarse particle NO₃⁻ via snow deposition may contribute to the nitrogen inventory in the snow surface. Measurements of surface snow provide experimental data that constrain the contribution of dry deposition of coarse particle NO₃⁻ to <7%. Wet deposition in falling snow appears to be the major contributor to the nitrate input to the snow.