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.     

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).     

Vertical distribution of gases and aerosols: The behaviour of ammonia and related components in the lower atmosphere

Vertical concentration profiles for NH₃, HNO₃ and HCl-gas and for NH₄⁺, NO₃⁻, SO²⁻₄, Cl⁻ and Na⁺ aerosol were obtained from a meteorological tower in the central part of the Netherlands. An upward NH₃ flux of 0.12 μgm⁻² s⁻¹ was calculated from the NH₃ profiles and meteorological data. From the HNO₃ profiles a maximum HNO₃ dry deposition velocity of 4 cm s⁻¹ was calculated. Good agreement was found between the measured concentration products [NH₃]_(g) × [HNO₃]_(g) and the theoretical values at temperatures above 0°C and relative humidities below 80%. In other cases, higher NH₃ and/or HNO concentrations in the gas phase were measured than theoretically predicted.     

Atmospheric deposition of macronutrients by pollen at a semi-remote site in northern Wisconsin

Pine pollen concentrations in air at a semi-remote site in northern Wisconsin attained levels of 18 and 25 μ m⁻³ in late May and early June of 1979 and 1981, respectively. The upper and lower limits for the deposition velocity of pine pollen at this site are approximately 30 and 1.3 cm s⁻¹, respectively. Consequently, the average annual pine pollen flux at this location for 1979 and 1981 was between 8.0 and 0.35 g m⁻². Deposition of total phosphorus and organic C by pollen dispersal are about 5–100% and 11–240%, respectively, of the measured bulk atmospheric loading rate in the region. Pine pollen fluxes of water-extractable K are about 10–230% of the average annual wet deposition, while the fluxes of waterextractable NO₃⁻ and SO₄⁻² by pollen appear to be negligible in comparison to the total atmospheric deposition (wet plus dry deposition) by other particles. The annual pine pollen flux to Crystal Lake, an oligotrophic seepage lake in the region, was estimated to be 6.5 g m⁻² during 1981. The deposition of total P by pollen to this lake was 5.8 kg a⁻¹, which is 45 % of the external input of total phosphorus. About 60% of the total P in samples of Pinus strobus and P. resinosa was dissolved reactive P, which is readily available for plant uptake. Because P is the limiting nutrient for many lacustrine systems and pine pollen dispersal coincides with the period of phytoplankton blooms in temperate-region lakes, this episodic input of P may represent an important source for seepage lakes whose external inputs are dominated by atmospheric deposition.     

Determination of Atmospheric Nitrogen Input to Lake Greenwood,South Carolina—I. PM Measurements

Abstract

The Reedy River branch of Lake Greenwood, SC, has repeatedly experienced summertime algal blooms, upsetting the natural system. This lake’s shallow depth makes it susceptible to atmospheric influence. A series of experiments were carried out in order to investigate the effect of atmospheric nitrogen deposition into the lake. Nitrogen was examined because of the insignificant phosphorus dry atmospheric flux and the unique nutrient demands of the dominant algae (Pithophora oedogonia) contributing to the blooms.

In this paper, results are presented of the experimental measurement of coarse and fine atmospheric concentrations of atmospheric particulate nitrogen adjacent to and in the watershed of the Reedy River (downtown Greenville) and Lake Greenwood. Experiments were carried out during four 24-hr periods in January 2001 and again during four 24-hr periods in March 2001. Results are presented here for atmospheric particulate nitrogen as well as other constituents of the airborne aerosol. Mass concentrations of PM_2.5 averaged 14.0 and 21 µg/m³ for Lake Greenwood and downtown Greenville, respectively. Mass concentrations of total suspended particulates (TSP) averaged 22.6 and 38.5 μg/m³ for Lake Greenwood and downtown Greenville, respectively. This ambient aerosol concentration was apportioned to its chemical constituents, and the greatest contributors to PM_2.5 mass were organics (45 and 42% for downtown Greenville and the lake, respectively) and sulfate (14.1 and 19.7% for downtown Greenville and the lake, respectively).

The information gathered here, despite its episodic nature, is important not only in determining atmospheric nitrogen but also in documenting the composition of aerosol in South Carolina, which so far has not been studied. In a companion paper, results for gaseous pollutants as well as thermodynamic modeling of the aerosol and nitrogen flux determinations are presented.     

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.     

Secondary organic aerosol formation from the oxidation of aromatic hydrocarbons in the presence of dry submicron ammonium sulfate aerosol

A laboratory study was conducted to examine formation of secondary organic aerosols. A smog chamber system was developed for studying gas–aerosol interactions in a dynamic flow reactor. These experiments were conducted to investigate the fate of gas and aerosol phase compounds generated from hydrocarbon–nitrogen oxide (HC/NO_x) mixtures irradiated in the presence of fine (<2.5 μm) particulate matter. The goal was to determine to what extent photochemical oxidation products of aromatic hydrocarbons contribute to secondary organic aerosol formation through uptake on pre-existing inorganic aerosols in the absence of liquid water films. Irradiations were conducted with toluene, p-xylene, and 1,3,5-trimethylbenzene in the presence of NO_x and ammonium sulfate aerosol, with propylene added to enhance the production of radicals in the system. The secondary organic aerosol yields were determined by dividing the mass concentration of organic fraction of the aerosol collected on quartz filters by the mass concentration of the aromatic hydrocarbon removed by reaction. The mass concentration of the organic fraction was obtained by multiplying the measured organic carbon concentration by 2.0, a correction factor that takes into account the presence of hydrogen, nitrogen, and oxygen atoms in the organic species. The mass concentrations of ammonium, nitrate, and sulfate concentrations as well as the total mass of the aerosols were measured. A reasonable mass balance was found for each of the aerosols. The largest secondary organic aerosol yield of 1.59±0.40% was found for toluene at an organic aerosol concentration of 8.2 μm⁻³, followed by 1.09±0.27% for p-xylene at 6.4 μg m⁻³, and 0.41±0.10% for 1,3,5-trimethylbenzene at 2.0 μg m⁻³. In general, these results agree with those reported by Odum et al. and appear to be consistent with the gas–aerosol partitioning theory developed by Pankow. The presence of organic in the aerosol did not affect significantly the hygroscopic properties of the aerosol.     

Local to regional emission sources affecting mercury fluxes to New York lakes

Lake-sediment records across the Northern Hemisphere show increases in atmospheric deposition of anthropogenic mercury (Hg) over the last 150 years. Most of the previous studies have examined remote lakes affected by the global atmospheric Hg reservoir. In this study, we present Hg flux records from lakes in an urban/suburban setting of central New York affected also by local and regional emissions. Sediment cores were collected from the Otisco and Skaneateles lakes from the Finger Lakes region, Cross Lake, a hypereutrophic lake on the Seneca River, and Glacial Lake, a small seepage lake with a watershed that corresponds with the lake area. Sediment accumulation rates and dates were established by ²¹⁰Pb. The pre-anthropogenic regional atmospheric Hg flux was estimated to be 3.0 μg m⁻² yr⁻¹ from Glacial Lake, which receives exclusively direct atmospheric deposition. Mercury fluxes peaked during 1971–2001, and were 3 to more than 30 times greater than pre-industrial deposition. Land use change and urbanization in the Otisco and Cross watersheds during the last century likely enhanced sediment loads and Hg fluxes to the lakes. Skaneateles and Glacial lakes have low sediment accumulation rates, and thus are excellent indicators for atmospheric Hg deposition. In these lakes, we found strong correlations with emission records for the Great Lakes region that markedly increased in the early 1900s, and peaked during WWII and in the early 1970s. Declines in modern Hg fluxes are generally evident in the core records. However, the decrease in sediment Hg flux at Glacial Lake was interrupted and has increased since the early 1990s probably due to the operation of new local emission sources. Assuming the global Hg reservoir tripled since the pre-industrial period, the contribution of local and regional emission sources to central New York lakes was estimated to about 80% of the total atmospheric Hg deposition.     

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.     

Altitude-dependent wet,dry and occult nitrogen deposition in an Alpine Region

From November 1995 to October 1996 and from October 1997 to September 1998, samples of wet precipitation, cloud water, as well as of reactive gases and particulate matter, were collected at three elevational levels (920 m, 1280 m and 1758 m a.s.l.) in Achenkirch, Austria. The samples were analysed for ammonium and nitrate in wet precipitation and in cloud water, for ammonia, nitric acid and nitrogen dioxide in the gas phase and for particulate ammonium and particulate nitrate in aerosol. Total nitrogen deposition was calculated combining measured concentrations in wet, dry and occult depositions with the corresponding deposition fluxes. Two multilayer deposition models were used for the calculation of dry and occult deposition. The total nitrogen input in 1995/96 was estimated to be 29 kg N ha⁻¹a⁻¹ at the Christlumkopf station (1758 m), 20 kg N ha⁻¹a⁻¹ at the Christlumalm station (1280 m) and 28 kg N ha⁻¹a⁻¹ at the Talboden station (930 m). Respective data for the 1997/98 observation period were 31 kg N ha⁻¹a⁻¹ at the Christlumkopf station (1758 m) and 18 kg N ha⁻¹a⁻¹ at the Mühleggerköpfl station (920 m). Critical Loads of nitrogen for coniferous forests were exceeded significantly near-source regions represented by areas of intense agricultural use and at high elevation sites.

     

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.     

The dry deposition of sulfur dioxide on a loblolly pine plantation

A concentration gradient/resistance model approach was used to determine the flux density, deposition velocity, and transport resistances for sulfur dioxide (SO₂ ) between the atmosphere and a loblolly pine (Pirms taeda L.) plantation. Measurements were made on 54 clear to partly sunny days during the period from June 1982 to May 1983. For this stand and these days, the average daylight flux density was 0.052 μg m⁻²s⁻¹ and the deposition velocity for SO₂ was 0.72±0.65 cms⁻¹. The average transport resistance for SO₂ includes the aerodynamic resistance (r_a), canopy resistance (r_c), and internal resistance corrected for solubility (r_ir). The values for these resistances were 15 ±4, 127 ±94 and 14+-39 s m⁻¹, respectively.     

Simultaneous use of relaxed eddy accumulation and gradient flux techniques for the measurement of sea-to-air exchange of dimethyl sulphide

The sea-to-air flux of the biogenic volatile sulphur compound dimethyl sulphide was assessed with the relaxed eddy accumulation (REA) and the gradient flux (GF) techniques from a stationary platform in the coastal Atlantic Ocean. Fluxes varied between 2 and 16 μmol m⁻² d⁻¹. Fluxes derived from REA were on average 7.1±5.03 μmol m⁻² d⁻¹, not significantly different from the average flux of 5.3±2.3 μmol m⁻² d⁻¹ derived from GF measurements. Gas transfer velocities were calculated from the fluxes and seawater DMS concentrations. They were within the range of gas transfer rates derived from the commonly used parameterizations that relate gas transfer to wind speed.     

Response of sediment calcium and magnesium species to the regional acid deposition in eutrophic Taihu Lake,China

Acid deposition causes carbonate dissolution in watersheds and leads to profound impacts on water chemistry of lakes. Here, we presented a detailed study on the seasonal, spatial, and vertical variations of calcium and magnesium species in the overlying water, interstitial water, and sediment profiles in eutrophic Taihu Lake under the circumstance of regional acid deposition. The result showed that both the acid deposition and biomineralization in Taihu Lake had effects on Ca and Mg species. In the lake water, calcium carbonate was saturated or over-saturated based on long-term statistical calculation of the saturation index (SI). On the sediment profiles, significant difference in Ca and Mg species existed between the surface sediment (0–10 cm) and deeper sediments (>10 cm). The interstitial water Ca²⁺ and Mg²⁺, ion-exchangeable Ca and Mg in the surface sediment were higher than those in the deeper sediment. In the spring, when the acid deposition is more intensive, the acid-extracted Ca and Mg in the surface sediment were lower than that in the deeper sediment in the northwest lake, due to carbonate dissolution caused by the regional acid deposition. Spatially, the higher concentration of acid-extracted Ca and Mg in the northwest surface sediment than that in the east lake was observed, indicating the pronounced carbonate biomineralization by algae bloom in the northwest lake. Statistical analysis showed that acid deposition exerted a stronger impact on the variation of acid-extracted Ca and Mg in the surface sediment than the biomineralization in Taihu Lake. For the total Ca and Mg concentration in the spring, however, no significant change between the surface and deeper sediment in the northwest lake was observed, indicating that the carbonate precipitation via biomineralization and the carbonate dissolution due to acidic deposition were in a dynamic balance. These features are of major importance for the understanding of combined effects of acid deposition and eutrophication on freshwater lakes.

     

Determination of atmospheric nitrogen input to Lake Greenwood,South Carolina--I. PM measurements

The Reedy River branch of Lake Greenwood, SC, has repeatedly experienced summertime algal blooms, upsetting the natural system. This lake's shallow depth makes It susceptible to atmospheric influence. A series of experiments were carried out in order to investigate the effect of atmospheric nitrogen deposition into the lake. Nitrogen was examined because of the insignificant phosphorus dry atmospheric flux and the unique nutrient demands of the dominant algae (Pithophora oedogonia) contributing to the blooms. In this paper, results are presented, of the experimental measurement of coarse and fine atmospheric concentrations of atmospheric particulate nitrogen adjacent to and in the watershed of the Reedy River (downtown Greenville) and Lake Greenwood. Experiments were carried out during four 24-hr periods in January 2001 and again during four 24-hr periods in March 2001. Results are presented here for atmospheric particulate nitrogen as well as other constituents of the airborne aerosol. Mass concentrations of PM2.5 averaged 14.0 and 21 microg/m3 for Lake Greenwood and downtown Greenville, respectively. Mass concentrations of total suspended particulates (TSP) averaged 22.6 and 38.5 microg/m3 for Lake Greenwood and downtown Greenville, respectively. This ambient aerosol concentration was apportioned to its chemical constituents, and the greatest contributors to PM2.5 mass were organics (45 and 42% for downtown Greenville and the lake, respectively) and sulfate (14.1 and 19.7% for downtown Greenville and the lake, respectively). The information gathered here, despite its episodic nature, is important not only in determining atmospheric nitrogen but also in documenting the composition of aerosol in South Carolina, which so far has not been studied. In a companion paper, results for gaseous pollutants as well as thermodynamic modeling of the aerosol and nitrogen flux determinations are presented.     

The sources and forms of phosphorus in marine aerosol particles and rain from Northern New Zealand

Various forms of phosphorus were measured in marine aerosol particles and rain samples collected from the northern tip of the North Island of New Zealand. Approximately 58 % of the total phosphorus in the aerosol particles was organic and 7 % was soluble in deionized water. The remaining 35 % was not released by treatment with potassium persulfate, and it was defined as a refractory fraction. Stepwise regression analyses suggested that (1) the concentrations of organic phosphorus in the aerosol particles were related to those of sodium, which was regarded as sea salt tracer, (2) the concentrations of water soluble phosphorus were correlated with those of aluminum, which was considered an indicator of crustal material and (3) total phosphorus was derived from the ocean and from the earth's crust. The mass particle-size distribution of the refractory and organic phosphorus combined was similar to that of sodium and aluminum. However, on submicrometer particles the concentrations of all forms of phosphorus appeared to increase relative to those of sodium, suggesting that small particle phosphorus may be derived from a non-marine source, possibly weathered crustal material or wind blown fertilizer. The wet deposition rates for water soluble and organic phosphorus were calculated to be 0.30 and 0.61 μg cm ⁻² y ⁻¹, respectively. The dry deposition of these two forms of phosphorus combined (0.14 μg cm ⁻² y ⁻¹ ) was clearly lower than the wet deposition rate. Total deposition of phosphorus to the site was estimated to be 1.5μgcm⁻²y⁻¹.     

Polycyclic aromatic hydrocarbon (PAH) deposition to and exchange at the air-water interface of Luhu, an urban lake in Guangzhou, China

Urban lakes are vulnerable to the accumulation of semivolatile organic compounds, such as PAHs from wet and dry atmospheric deposition. Little was reported on the seasonal patterns of atmospheric deposition of PAHs under Asian monsoon climate. Bulk (dry + wet) particle deposition, air-water diffusion exchange, and vapour wet deposition of PAHs in a small urban lake in Guangzhou were estimated based on a year-round monitoring. The total PAH particle deposition fluxes observed were 0.44-3.46 μg m⁻² day⁻¹. The mean air-water diffusive exchange flux was 20.7 μg m⁻² day⁻¹. The vapour deposition fluxes of PAHs ranged 0.15-8.26 μg m⁻² day⁻¹. Remarkable seasonal variations of particulate PAH deposition, air-water exchange fluxes and vapour wet deposition were influenced by seasonal changes in meteorological parameters. The deposition fluxes were predominantly controlled by the precipitation intensity in wet season whereas by atmospheric concentration in dry season.     

Determination of Atmospheric Nitrogen Input to Lake Greenwood,South Carolina: Part 2—Gaseous Measurements and Modeling

Abstract

The Reedy River branch of Lake Greenwood, SC, has repeatedly experienced summertime algal blooms, upsetting the natural system. A series of experiments were carried out to investigate atmospheric nitrogen (N) input into the lake. N was examined because of the insignificant phosphorus dry atmospheric flux and the unique nutrient demands of the dominant algae (Pithophora oedogonia) contributing to the blooms. Episodic atmospheric measurements during January and March 2001 have shown that the dry N flux onto the lake ranged from 0.9 to 17.4 kg N/ha-yr, and on average is caused by nitric acid (HNO₃; 31%), followed by nitrogen dioxide (NO₂; 23%), fine ammonium (NH₄ ⁺; 20%), coarse nitrate (NO₃ ^?; 16%), fine NO₃ ⁺ (5%), and coarse NH₄ ⁺ (5%). Similar measurements in Greenville, SC (the upper watershed of the Reedy River), showed that the dry N deposition flux there ranged from 1.4 to 9.7 kg N/ha-yr and was mostly caused by gaseous deposition (40% NO₂ and 40% HNO₃). The magnitude of this dry N deposition flux is comparable to wet N flux as well as other point sources in the area. Thermodynamic modeling showed low concentrations of ammonia, relative to the particulate NH₄ ⁺ concentrations.     

Sedimentation and seasonal variation of hexachlorocyclohexanes in sediments in a eutrophic lake,China

Hexachlorocyclohexane (HCH) concentrations in sediments and sediment trap fluxes of particulate organic carbon and HCHs were measured bi-weekly from March 31 to October 18, 2006 in an urban eutrophic lake in Tianjin, China, in order to investigate sedimentation and seasonal variation of HCHs in sediments. HCH concentrations (dry weight basis) ranged from 2.2 to 20.2 ng/g (mean 7.7 ng/g) in surface sediments and from 26.6 to 972.7 ng/g (mean 187.0 ng/g) in settling particles, respectively. A clear seasonal variation in HCH sedimentation and HCH concentrations in sediments was observed. The maximal HCH deposition occurred following a spring phytoplankton bloom. The average flux of HCHs to sediment was approximately 21-fold higher in April to mid-June as compared to late June to October. This was attributed to the high vertical fluxes at the end of the spring phytoplankton bloom. The maximum values of HCH concentrations in sediments were observed in mid-June to late July. Concentrations of HCHs in sediments from the eutrophic lake were well-correlated with organic carbon contents in sediments. The annual sediment trap flux of HCHs in the eutrophic lake, which was estimated using data obtained in the eutrophic lake, was 117 μ g/m² yr, about 72% of which was attributed to the sedimentation corresponding to spring bloom phytoplankton deposition in late May to mid-June. The high sediment trap flux of HCHs in the eutrophic lake was related to serious local contamination.     

Particle-bound PAH content in ambient air

Ambient air samples from a traffic intersection, an urban site and a petrochemical-industrial site (PCI) were collected by using several dry deposition plates, two Microorifice uniform deposited impactors (MOUDIs), one Noll Rotary Impactor (NRI) and several PS-1 (General Metal Work) samplers from March 1994 to June 1995 in southern Taiwan, to characterize the atmospheric particle-bound PAH content of these three areas. Twenty-one individual polycyclic aromatic hydrocarbons (PAHs) were analyzed primarily by using a gas chromatograph/mass spectrometer (GC/MS). In general, the sub-micron particles have a higher PAH content. This is due to the fact that soot from combustion sources consists primarily of fine particles and has a high PAH content. In addition, a smaller particle has a higher specific surface area and therefore may contain more organic carbon, which allows for more PAH adsorption. For a particle size range between 0.31 and 3.2 microm, both Urban/Traffic and PCI/Traffic ratios of particle-bound total-PAH content have the lowest values, ranging from 0.25 to 0.28 (mean = 0.26) and from 0.07 to 0.13 (mean = 0.10), respectively. This indicates that, during the accumulation process, the PAH mass shifted from a particle phase to a gas phase, or the particles aggregated with lower PAH-content particles, resulting in a reduction in particle-bound PAH content. By using the particle size distribution data, the dry deposition model in this study can provide a good prediction for the PAH content of dry deposition materials. In general, lower molecular weight PAHs had a larger fraction of dry deposition flux contributed by the gas phase; for 2-ring PAH (50.4, 46.3 and 28.4%), 3-ring PAHs (15.2, 15.4 and 11.7%) and 4-ring PAHs (13.0, 3.60 and 5.01%) for the traffic intersection, urban and PCI sites, respectively. For higher molecular weight PAHs-5-ring, 6-ring and 7-ring PAHs-their cumulation fraction (F%) of dry deposition flux contributed by the gas phase was lower than 3.26%. At the traffic intersection, urban and PCI sites, the mass median diameter of dry deposition materials (MMD(F)) of individual PAHs was between 25.3 and 49.6 microm, between 27.6 and 43.9 microm, and between 19.1 and 41.9 microm, respectively. This is due to the fact that PAH dry-deposition primarily resulted from gravitational settling of the coarse particulates (> 10 microm).