Spatial character of polychlorinated biphenyls from soil and respirable particulate matter in Taiyuan, China

As one of China’s great metropolises, Taiyuan is affected by heavy chemical industry and manufacture of chemical products, and faces pollution from polychlorinated biphenyls (PCBs). Therefore, this study was conducted to determine the PCB concentrations in various environmental media in Taiyuan. We collected 15 soil samples, 34 respirable particulate matter (PM) samples (17 of PM_2.5 and 17 of PM₁₀) from urban areas of Taiyuan, and measured a total of 144 PCB congeners (including some coeluting PCB congeners). The total PCB concentrations were 51–4.7 × 10³ pg g⁻¹ in soil, 27–1.4 × 10² pg m⁻³ in PM_2.5 and 16–1.9 × 10² pg m⁻³ in PM₁₀. Of the PCB homologues, the dominant PCBs detected in the various media were all tri-CBs. Soil was relatively the most polluted media. Furthermore, principal-component analysis revealed that the major PCB source in Taiyuan may be associated with the main commercial PCB through long-range transmission. Toxic equivalency (TEQ) concentrations (based on ten dioxin-like PCBs) ranged from N.D. to 5.9 × 10⁻³ pg-WHO TEQ g⁻¹ in soil, 2.0 × 10⁻⁴–3.4 × 10⁻³ pg-WHO TEQ m⁻³ and 1.0 × 10⁻⁴–1.2 × 10⁻³ pg-WHO TEQ m⁻³ in PM_2.5 and PM₁₀, respectively. In previous studies, PCBs were not a severe component of contaminant in Taiyuan; however, this study suggested there is a potential threat of human exposure to PCBs for residents of Taiyuan.     

Description and evaluation of a model of deposition velocities for routine estimates of dry deposition over North America. Part II: review of past measurements and model results

Numerical sensitivity tests and four months of complete model runs have been conducted for the Routine Deposition Model (RDM). The influence of individual model inputs on dry deposition velocity as a function of land-use category (LUC) and pollutant (SO₂, O₃, SO²⁻₄ and HNO₃) were examined over a realistic range of values for solar radiation, stability and wind speed. Spatial and temporal variations in RDM deposition velocity (V_d) during June – September 1996 time period generated using meteorological input from a mesoscale model run at 35 km resolution over north-eastern North America were also examined. Comparison of RDM V_d values to a variety of measurements of dry deposition velocities of SO₂, O₃, SO²⁻₄ and NHO₃ that have been reported in the literature demonstrated that RDM produces realistic results. Over northeastern NA RDM monthly averaged dry deposition velocities for SO₂ vary from 0.2 to 3.0 cm s⁻¹ with the highest deposition velocities over water surfaces. For O₃, the monthly averaged dry deposition velocities are from 0.05 to 1.0 cm s⁻¹ with the lowest values over water surfaces and the highest over forested areas. For HNO₃, the monthly averaged dry deposition velocities have the range of 0.5 to 6 cm s⁻¹, with the highest values for forested areas. For SO²⁻₄, they range from 0.05–1.5 cm s⁻¹, with the lowest values over water and the highest over forest. The monthly averaged dry deposition velocities for SO₂ and O₃ are higher in the growing season compared to the fall, but this behaviour is not apparent for HNO₃ and sulphate. In the daytime, the hourly averaged dry deposition velocities for SO₂, O₃, SO²⁻₄ and HNO₃ are higher than that in the nighttime over most of the vegetated area. The diurnal variation is most evident for surfaces with large values for leaf area index (LAI), such as forests. Based on the results presented in this paper, it is concluded that RDM V_d values can be combined with measured air concentrations over hourly, daily or weekly periods to determine dry deposition amounts and with wet deposition measurements to provide seasonal estimates of total deposition and estimates of the relative importance of dry deposition.     

The contribution of dry deposited ammonia and sulphur dioxide to the composition of precipitation from continuously open gauges

A series of experiments using bulk precipitation collectors of the type used in the UK precipitation chemistry network measured the amounts of NH₄⁺, SO₄²⁻ and other ions that could be washed from funnels (diameter 15 cm) exposed to a wide range of NH₃ and SO₂ concentrations over periods from hours to days. In dry conditions, the average deposition flux of NH₃ was between 50 and 120 nmol NH₄⁺ funnel⁻¹ d⁻¹ (0.1–0.3 kg N ha⁻¹ yr⁻¹), and was independent of the concentration of NH₃. Dry deposition of NH₃ to wet funnels at small NH₃ concentrations was almost 5 times that to dry funnels under the same conditions (average 240 nmol funnel⁻¹ d⁻¹; 0.7 kg ha⁻¹ yr⁻¹), and increased with increasing NH₃ concentrations. The amount of NH₄⁺ ions remaining on the funnel surface was inversely proportional to the vapour pressure deficit during the experiment. This result was interpreted as a dependence on the duration of surface wetness, with greater deposition of NH₄⁺ when evaporation rates of surface water were small.The amount of SO₂ deposited on funnel surfaces was closely related to the amount of NH₃ deposited, in both wet and dry conditions, but was not strongly correlated with the SO₂ concentration. At low NH₃ and SO₂ concentrations the average deposition to dry funnels was 70 nmol SO₄²⁻ funnel⁻¹ d⁻¹ (0.5 kg ha⁻¹ yr⁻¹), and to wet funnels was approximately 2.5 times larger. The results are interpreted in terms of the balance between the rate of evaporation of surface water, and the rate of oxidation of SO₂, which leads to the ‘fixing’ of NH₄⁺ ions on the surface as involatile salts.It is predicted that dry deposition of NH₃ to funnel surfaces across the UK Secondary Network could account for as much as one-half of the measured bulk wet deposition at sites where wet deposition of NH₄–N is small. The amount of dry deposition depends on how long and how often funnel surfaces are wetted by rain or dew, and on the air concentrations of NH₃. These predictions are based on funnels being wetted only once per day. More frequent wetting would increase the contribution from dry deposition, and the consequent overestimate of wet deposition of NH₄–N across the UK by using data obtained from bulk collectors. To some extent this overestimate may be offset by microbial degradation and loss of NH₄–N in weekly bulk precipitation samples during collection and storage.     

Comportement photochimique du nitro-4 phenol en solution aqueuse

The quantum yield of the phototransformation of 4-nitrophenol has been evaluated as 4.5×10⁻⁵±0.6×10⁻⁵ at pH=2; at 3.0×10⁻⁵±0.6×10⁻⁵ at pH=5.5; 1.8×10⁻⁵±0.5×10⁻⁵ at pH=8.3. However the half-life is relatively low and no accumulation of aromatic or quinonic products was observed. Hydroquinone (QH₂) is the main organic primary product formed when an air-saturated or degassed solution was irradiated in 365 nm monochromatic light (about 80% of the 4-nitrophenol initially converted at pH=5.5 in the absence of oxygen). In air-saturated neutral or acidic solution, the formation of NO⁻₃ ions accounted for about 80% of the 4-nitrophenol converted, but in degassed medium a mixture NO : NO⁻₂ : NO⁻₃ is formed. An heterolytical mechanism of photohydrolysis with primary formation of QH₂ and HNO₂ is suggested. Several by-products as benzoquinone, 4-nitrosophenol, 4-nitrocatechol and nitrohydroquinone are formed according to the conditions. Many secondary reactions are involved as the disproportionation or the oxidation of HNO₂, the oxidation of QH₂ by HNO₂ and oxidations induced by excitation of NO⁻₂ and NO⁻₃.     

Concentrations of carbon gases and oxygen and their emission ratios from the combustion of rice hulls in a wind tunnel

Rice hulls are widely burnt in agricultural fields in Asia because it is difficult to find other uses for them. Farmers burn rice hulls usually under incomplete combustion conditions to avoid accidental fires. In this study we investigated carbon gas emissions from rice hull fires at controlled wind speeds in a wind tunnel to clarify the effect of wind on such fires. Burning of the rice hulls resulted in relatively incomplete combustion: the ratio of [CO] to [CO₂] was high, >0.2, except when burning occurred at high wind speeds. Distinct differences in the carbon ratios of emitted carbon gases (CO₂, CO, CH₄, and nonmethane volatile organic compounds [NMVOC]) were found between high and low wind speeds: at high wind speeds, flames were usually present, and the CO₂ contribution to total carbon gases was higher; at low wind speeds, the NMVOC and CH₄ contributions to total carbon gases were greater. Therefore, a compensatory relationship existed between NMVOC and CH₄ and CO₂. Additionally, the ratio of [consumed O₂] to [CO₂] was <1 during the smoldering phase of combustion and >1 during the charcoal phase, synchronous with changes in [CH₄] and [NMVOC].     

The change of gaseous carbon fluxes following the switch of dominant producers from macrophytes to algae in a shallow subtropical lake of China

Successions of lake ecosystems from clear-water, macrophyte-rich conditions into turbid states with abundant phytoplankton have taken place in many shallow lakes in China. However, little is know about the change of carbon fluxes in lakes during such processes. We conducted a case study in Lake Biandantang to investigate the change of carbon fluxes during such a regime shift. Dissolved aquatic carbon and gaseous carbon (methane (CH₄) and carbon dioxide (CO₂)) across air–water interface in three sites with different vegetation covers and compositions were studied and compared. CH₄ emissions from three sites were 0.62±0.36, 0.70±0.36, and 1.31±0.57 mg m⁻² h⁻¹, respectively. Correlation analysis showed that macrophytes, rather than phytoplankton, directly positively affected CH₄ emission. CO₂ fluxes of three sites in Lake Biandantang were significantly different, and the average values were 77.8±20.4, 52.2±14.1 and 3.6±26.8 mg m⁻² h⁻¹, respectively. There were an evident trend that the larger macrophyte biomass, the lower CO₂ emissions. Correlation analysis showed that in different sites, dominant plant controlled CO₂ flux across air–water interface. In a year cycle, the percents of gaseous carbon release from lake accounting for net primary production were significantly different (from 39.3% to 2.8%), indicating that with the decline of macrophytes and regime shift, the lake will be a larger carbon source to the atmosphere.     

Do aerosols act as catalysts in the OH radical initiated atmospheric oxidation of volatile organic compounds?

Smog chamber/FTIR techniques were used to study the relative reactivity of OH radicals with methanol, ethanol, phenol, C₂H₄, C₂H₂, and p-xylene in 750 Torr of air diluent at 296±2 K. Experiments were performed with, and without, 500–8000 μg m⁻³ (4000–50 000 μm² cm⁻³ surface area per volume) of NaCl, (NH₄)₂SO₄ or NH₄NO₃ aerosol. In contrast to the recent findings of Oh and Andino (Atmospheric Environment 34 (2000) 2901, 36 (2002) 149; International Journal of Chemical Kinetics 33 (2001) 422) there was no discernable effect of aerosol on the rate of loss of the organic compounds via reaction with OH radicals. Gas kinetic theory arguments cast doubt upon the findings of Oh and Andino. The available data suggest that the answer to the title question is “No”. As part of this work the rate constants for reactions of OH radicals with methanol, ethanol, and phenol in 750 Torr of air at 296 K were determined to be: k_OH+CH3OH=(8.12±0.54)×10⁻¹³, k_OH+C2H5OH=(3.47±0.32)×10⁻¹² and k_OH+phenol=(3.27±0.31)×10⁻¹¹ cm³ molecule⁻¹ s⁻¹.     

An aerosol flow tube study of the interaction of N2O5 with calcite, Arizona dust and quartz

The interaction of N₂O₅ with dispersed samples of Arizona Test Dust (ATD), Calcite (CaCO₃) and quartz (SiO₂) was investigated at varying relative humidity using an aerosol flow reactor. Reactive uptake coefficients, γ, obtained at close to zero relative humidity were (4.8 ± 0.7) × 10⁻³ for CaCO₃, (8.6 ± 0.6) × 10⁻³ for Quartz and (9.8 ± 1.0) × 10⁻³ for ATD. In the case of calcite, evidence was obtained for an enhanced rate of uptake at relative humidities above ≈ 50%. The results are compared to literature values obtained using bulk substrates and to previous aerosol uptake data on Saharan dust.     

Assessment of traffic-related air pollution in the urban streets before and during the 2008 Beijing Olympic Games traffic control period

In order to investigate the air quality and the abatement of traffic-related pollution during the 2008 Olympic Games, we select 12 avenues in the urban area of Beijing to calculate the concentrations of PM₁₀, CO, NO₂ and O₃ before and during the Olympic traffic controlling days, with the OSPM model.Through comparing the modeled results with the measurement results on a representative street, the OSPM model is validated as sufficient to predict the average concentrations of these pollutants at street level, and also reflects their daily variations well, i.e. CO presents the similar double peaks as the traffic flow, PM₁₀ concentration is influenced by other sources. Meanwhile, the model predicts O₃ to stay less during the daytime and ascend in the night, just opposite to NO₂, which reveals the impact of photochemical reactions. In addition, the predicted concentrations on the windward side often exceed the leeward side, indicating the impact of the special street shape, as well as the wind.The comparison between the predicted street concentrations before and during the Olympic traffic control period shows that the overall on-road air quality was improved effectively, due to the 32.3% traffic flow reduction. The concentrations of PM₁₀, CO and NO₂ have reduced from 142.6 μg m⁻³, 3.02 mg m⁻³ and 118.7 μg m⁻³ to 102.0 μg m⁻³, 2.43 mg m⁻³ and 104.1 μg m⁻³. However, the different pollutants show diverse changes after the traffic control. PM₁₀ decreases most, and the reduction effect focusing on the first half-day even clears the morning peak, whereas CO and NO₂ have even reductions to minify the daily fluctuations on the whole. Opposite to the other pollutants, ozone shows an increase of concentration. The average reduction rate of PM₁₀, CO, NO₂ and O₃ are respectively 28%, 19.3%, 12.3% and −25.2%. Furthermore, the streets in east, west, south and north areas present different air quality improvements, probably induced by the varied background pollution in different regions around Beijing, along with the impact of wind force. This finding suggests the pollution control in the surrounding regions, not only in the urban area.     

A study of the atmospheric reaction of CH3S with O3 as a function of temperature

The atmospheric reaction of the methylthiyl radical (CH₃S) with O₃ was investigated as a function of temperature (259–381 K), in the pressure range of 25–300 Torr, using the technique of laser photolysis/laser-induced fluorescence. The resulting Arrhenius expression, with an uncertainty of ±2σ, was k₁(T=259–381 K)=(1.02±0.30)×10⁻¹² exp[(432±77) K/T] cm³ molecule⁻¹ s⁻¹. The obtained rate constant k₁ was independent of pressure over the limited range employed. Our results are compared with the previous studies carried out, at single temperature and as a function of temperature, by different techniques.     

Short-term effect of increasing nitrogen deposition on CO2, CH4 and N2O fluxes in an alpine meadow on the Qinghai-Tibetan Plateau,China

An increasing nitrogen deposition experiment (2 g N m^?2 year^?1) was initiated in an alpine meadow on the Qinghai-Tibetan Plateau in May 2007. The greenhouse gases (GHGs), including CO₂, CH₄ and N₂O, was observed in the growing season (from May to September) of 2008 using static chamber and gas chromatography techniques. The CO₂ emission and CH₄ uptake rate showed a seasonal fluctuation, reaching the maximum in the middle of July. We found soil temperature and water-filled pore space (WFPS) were the dominant factors that controlled seasonal variation of CO₂ and CH₄ respectively and lacks of correlation between N₂O fluxes and environmental variables. The temperature sensitivity (Q₁₀) of CO₂ emission and CH₄ uptake were relatively higher (3.79 for CO₂, 3.29 for CH₄) than that of warmer region ecosystems, indicating the increase of temperature in the future will exert great impacts on CO₂ emission and CH₄ uptake in the alpine meadow. In the entire growing season, nitrogen deposition tended to increase N₂O emission, to reduce CH₄ uptake and to decrease CO₂ emission, and the differences caused by nitrogen deposition were all not significant (p < 0.05). However, we still found significant difference (p < 0.05) between the control and nitrogen deposition treatment at some observation dates for CH₄ rather than for CO₂ and N₂O, implying CH₄ is most susceptible in response to increased nitrogen availability among the three greenhouse gases. In addition, we found short-term nitrogen deposition treatment had very limited impacts on net global warming potential (GWP) of the three GHGs together in term of CO₂-equivalents. Overall, the research suggests that longer study periods are needed to verify the cumulative effects of increasing nitrogen deposition on GHG fluxes in the alpine meadow.     

Colloid and suspended particle migration experiments in a granite fracture

To determine the mobility of colloids (0.001–0.45 μm) and suspended particles (> 0.45 μm) in granite fractures, laboratory particle-migration and conservative tracer studies have been carried out in a natural fracture within a large granite block, with overall dimensions of 83×90×60 cm. Flow fields within this horizontal fracture were controlled through a set of 9 boreholes drilled orthogonally to the fracture. Laboratory experiments were performed using a range of average water velocities which contained values low enough to closely approximate the natural flow velocities of < 2 m yr⁻¹ in plutonic rocks of the Canadian Shield. The particles used had diameters between 0.02 and 22 μm, and included latex spheres, glass spheres and colloidal silica. Migration experiments were carried out with a filtered groundwater, ionic strength of 0.01 mol kg⁻¹, obtained from a granite fracture within the Whiteshell Research Area of Manitoba. Flushing experiments showed that suspended particles as large as 40 μm could be mobilized from the fracture surface. The mobility of suspended particles was significantly less than that of colloids. However, within the size range of colloids used in these studies (0.022–0.090 μm), colloid size did not affect colloid migration. Although, in general, colloids eluted ahead of the conservative tracer, colloid mobility was significantly reduced when the average groundwater velocity dropped below between 32 and 240 m yr⁻¹. Colloid transport was found to be very sensitive to flow path and flow direction.     

The potential inhalation hazard posed by dioxin-contaminated soil

Conservative models were used to estimate the airborne concentrations of 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD) vapor and particulates originating from soil containing 100 ppb TCDD. The upper-bound estimates were 3.25 pg/m³ of airborne TCDD vapor on-site and 0.51 pg/m³ for TCDD vapor 100 meters downwind. The TCDD air concentration on-site due to suspended particulate is estimated to be 1.4 pg/m³, based on a TSP level of 0.07 mg/m³. Assuming 70 years of continuous exposure to these concentrations, the upper-bound cancer risks determined from the Jury model were estimated to be 9.4 × 10⁻⁶ to 1.1 × 10⁻⁴ and 1.5 × 10⁻⁶ to 1.7 × 10⁻⁵ for inhalation of on- and off-site vapor, respectively, and 4.1 × 10⁻⁶ to 4.6 × 10⁻⁵ for dust inhalation. Since few sites have average soil concentrations as high as 100 ppb TCDD, this worst-case analysis indicates that inhalation will rarely, if ever, be a significant route of exposure to TCDD-contaminated soil. Experimental results support this claim and point to much lower risk estimates (8.4 × 10⁻⁹ to 9.9 × 10⁻⁸), suggesting that the parameters used in the Jury model are likely to overestimate the actual airborne levels of TCDD at contaminated sites.     

The role of wind field, mixing height and horizontal diffusivity investigated through two lagrangian particle models

Two Lagrangian particle models, APOLLO and MILORD, were used to simulate the first ETEX experiment. The role played by wind field, mixing height h and horizontal diffusivity K_H appeared to be the most important aspects to be studied. The sensitivity to the accuracy of the input advection field was studied through the application of APOLLO using different ECMWF data sets differing in space and time resolution and in being forecasted or analysed, corresponding to the real-time, emergency-like condition, and to the a posteriori benchmark simulation. The role of h and K_H was investigated by running both APOLLO and MILORD with different parameterisations, and comparing the model results between them and with the available observations.The model evaluation was carried out through a set of statistical indexes computed on three hourly average concentrations paired in space and time and time-integrated concentrations. It was found that the quality of the input wind field plays a major role in predicting with sufficient accuracy the plume position and extension after the first 24 h from the beginning of the release. The best-model results are obtained with large values of K_H (in the range of 2.5×10⁴–4.5×10⁴ m² s^-1), which confirms the need to enhance the horizontal diffusion, in order to include the advection fluctuations unresolved by large-scale meteorological fields. A fixed value of h in the range 1000–1500 m seems to be more efficient than space and time variable h computed with standard algorithms. A reasonable explanation for this result is given, based on the consideration that in the long range, particles diffuse also in the residual layer above the stable nocturnal boundary layer.     

High concentrations and dry deposition of reactive nitrogen species at two sites in the North China Plain

Atmospheric concentrations of major reactive nitrogen (N_r) species were quantified using passive samplers, denuders, and particulate samplers at Dongbeiwang and Quzhou, North China Plain (NCP) in a two-year study. Average concentrations of NH₃, NO₂, HNO₃, pNH₄⁺ and pNO₃⁻ were 12.0, 12.9, 0.6, 10.3, and 4.7 μg N m⁻³ across the two sites, showing different seasonal patterns of these N_r species. For example, the highest NH₃ concentration occurred in summer while NO₂ concentrations were greater in winter, both of which reflected impacts of N fertilization (summer) and coal-fueled home heating (winter). Based on measured N_r concentrations and their deposition velocities taken from the literature, annual N dry deposition was up to 55 kg N ha⁻¹. Such high concentrations and deposition rates of N_r species in the NCP indicate very serious air pollution from anthropogenic sources and significant atmospheric N input to crops.     

Trans-boundary air pollution over remote islands in Japan: observed data and estimates from a numerical model

Observations of air pollutants were conducted in remote Japanese islands (Oki Island and Okinawa Island) in early spring to clarify the extent of trans-boundary air pollution from the Asian continent. A three-dimensional Eulerian model calculation, which included parameters on emission, transport and transformation of sulfur oxides, nitrogen oxides and ammonia, was performed to compile sulfate isosurface concentrations over the observational sites. Concentrations of non-sea-salt sulfate (nss-SO₄²⁻) of greater than 10 μg m⁻³ were observed at Oki after the northeastward passage of low-pressure systems in the Sea of Japan. At these times, the weather showed a typical winter pattern and air pollutants over China were transported southeastward to Japan with the northwesterly wind. The model calculation reproduced the observed variations of nss-SO₄²⁻ concentration well, except for one case in which the model calculation could not reproduce the extremely low nss-SO₄²⁻ concentration observed on 8 March. In Hedo (Okinawa Island), we observed long-lasting (3 days) medium concentrations of nss-SO₄²⁻ (approximately 5 μg m⁻³). Although the model reproduced these observed medium concentrations well, in general the observed results were reproduced better for Oki than for Hedo. Under the synoptic weather conditions of early spring, high concentrations of nss-sulfate were sometimes transported to these remote Japanese islands from areas of continental Asia with a strong outflow of air pollutants.     

Transport and transformation of sulfur compounds over East Asia during the TRACE-P and ACE-Asia campaigns

On the basis of the recently estimated emission inventory for East Asia with a resolution of 1×1°, the transport and chemical transformation of sulfur compounds over East Asia during the period of 22 February through 4 May 2001 was investigated by using the Models-3 Community Multi-scale Air Quality (CMAQ) modeling system with meteorological fields calculated by the regional atmospheric modeling system (RAMS). For evaluating the model performance simulated concentrations of sulfur dioxide (SO₂) and aerosol sulfate (SO₄²⁻) were compared with the observations on the ground level at four remote sites in Japan and on board aircraft and vessel during the transport and chemical evolution over the Pacific and Asian Pacific regional aerosol characterization experiment field campaigns, and it was found that the model reproduces many of the important features in the observations, including horizontal and vertical gradients. The SO₂ and SO₄²⁻ concentrations show pronounced variations in time and space, with SO₂ and SO₄²⁻ behaving differently due to the interplay of chemical conversion, removal and transport processes. Analysis of model results shows that emission was the dominant term in regulating the SO₂ spatial distribution, while conversion of SO₂ to SO₄²⁻ in the gas phase and the aqueous phase and wet removal were the primary factors that controlled SO₄²⁻ amounts. The gas phase and the aqueous phase have the same importance in oxidizing SO₂, and about 42% sulfur compounds (25% in SO₂) emitted in the model domain was transported out, while about 57% (35% by wet removal processes) was deposited in the domain during the study period.     

Effective diffusivity of the uranyl ion in a granite from Inada, Ibaraki, Japan

The effective diffusivity of uranium(VI) in Inada granite has been determined by through-diffusion. Experiments were performed at room temperature (20–25°C) in a 0.1 mol 1⁻¹ KCl solution where uranium is present predominantly as the poorly sorbing UO₂²⁺. An effective diffusivity (D_e) of (3.6 ± 1.6) × 10⁻¹⁴ m² s⁻¹ was obtained, close to that for uranine (nonsorbing organic tracer), but one order of magnitude lower than those obtained for Sr²⁺ and NpO₂⁺, and two orders of magnitude lower than that obtained for I⁻. According to well established theory, a proportional relationship exists between D_e and the diffusivity in the bulk of the solution (D_v). The effective diffusivity obtained in granite was not proportional to D_v. This agrees with results obtained for effective diffusivity in a Swedish granite. The ratio D_e/D_v was found to be not constant but increased with D_e or D_v. This result suggests a limit to the application of the theory.     

Chemical characteristics of precipitation at metropolitan Newark in the US East Coast

To investigate the chemical characteristics of precipitation in the polluted coastal atmosphere, a total of 46 event-based precipitation samples were collected using a wet-only automatic precipitation collector from September 2006 to October 2007 at metropolitan Newark, New Jersey in the US East Coast. Samples were analyzed by ion chromatography for the concentrations of major inorganic ions (Cl⁻, NO₃⁻, SO₄²⁻, F⁻, NH₄⁺, Ca²⁺, Mg²⁺, Na⁺, K⁺) and organic acid species (CH₃COO⁻, HCOO⁻, CH₂(COO)₂²⁻, C₂O₄²⁻). Selected trace metals (Sb, Pb, Al, V, Fe, Cr, Co, Ni, Cu, Zn, Cd) in samples were determined by ICPMS. Mass concentration results show that SO₄²⁻ was the most dominant anion accounting for 51% of the total anions, controlling the acidity of the precipitation. NH₄⁺ accounted for 48.6% of the total cations, dominating the precipitation neutralization. CH₃COO⁻ and HCOO⁻ were the two dominant water-soluble organic acid species, accounting for 42% and 40% of the total organic acids analyzed, respectively. Al, Zn and Fe were the three major trace metals in precipitation, accounting for 34%, 27%, and 25% of the total mass of metals analyzed. The pH values in precipitation ranged from 4.4 to 4.9, indicating an acidic nature. Enrichment Factor (EF) Analysis showed that Na⁺, Cl⁻, Mg²⁺ and K⁺ in the precipitation were primarily of marine origin, while most of the Fe, Co and Al were from crust sources. Pb, V, Cr, Ni were moderately enriched with EFs ranging 43–410, while Zn, Sb, Cu, Cd and F⁻ were highly enriched with EFs > 700, indicating significant anthropogenic influences. Factor analysis suggests 6 major sources contributing to the observed composition of precipitation at this location: (1) nitrogen-enriched soil, (2) secondary pollution processes, (3) marine sources, (4) incinerations, (5) oil combustions, and (6) malonate–vanadium enriched sources. To further explore the source–precipitation event relationships and seasonality, cluster analysis was performed for all precipitation events. Results show that about half of the precipitation events were characterized by mixed sources. Significant influences of nitrogen-enriched soil and marine sources were associated with precipitation events in spring and autumn, while secondary pollution processes, incineration and oil combustion contributed greatly in summer.     

Development of steady-state phosphate concentrations in septic system plumes

Long-term monitoring of PO₄⁻³ behaviour in a well-defined septic system plume on calcareous sand (Cambridge site) shows that, after 17 yr of system operation, a distinct PO₄⁻³ plume (PO₄⁻³−P > 1 mg L⁻¹) is present extending 20 m downgradient from the infiltration bed. The PO₄³⁻ plume migration velocity is 1 m yr⁻¹, reflecting retardation by a factor of 20 compared to the groundwater velocity. During monitoring between years 10 to 17, an expanding steady-state zone was noted below the infiltration bed where PO₄³⁻ −P levels remained consistently near 4 mg L⁻¹, a value 25% lower than the average effluent value (6.3 mg L⁻¹). The pattern of attenuation — a 25% mass loss in the 2-m-thick vadose zone, then little further attenuation along the flowpath — is suggestive of a condition of equilibrium with a controlling phosphate mineral phase. Chemical equilibrium modelling shows supersaturation with respect to hydroxylapatite and variscite. Four other field sites are identified from the literature and from our work where similar steady-state PO₄³⁻ zones are present in septic system plumes. In these, steady-state levels range from 15% to 68% of effluent values, with lower concentrations observed in the more acidic plumes, again indicative of a mineral solubility control, possibly variscite.PO₄³⁻ behaviour in these plumes suggests that, although P migration velocity is controlled by the processes of sorption, the magnitude of PO₄³⁻ that is present is governed by the constraints of phosphate mineral solubility. When septic systems on sands are located relatively close to sensitive surface water bodies and when long-term downgradient impact is the primary concern, more attention should be focused on the geochemical conditions that control PO₄³⁻ mineral solubility rather than only on the sorption characteristics of the sediment.