Evaluation of a diode laser based photoacoustic instrument combined with preconcentration sampling for measuring surface–atmosphere exchange of ammonia with the aerodynamic gradient method

We present here a novel instrument for measuring surface–atmosphere exchange fluxes of ammonia. The instrument is the upgraded version of a recently developed near-infrared diode laser based photoacoustic ammonia concentration monitoring instrument, i.e. the original instrument is supplemented with two additional sampling lines, an appropriate gas handling system and an advanced software controlling gradient measurements. As a result of these developments, ammonia concentration can be measured simultaneously at three different heights above the ground and ammonia fluxes can be calculated from these data using the aerodynamic gradient method. The instrument operates fully automatically, requires minimal maintenance and has a temperature controlled, waterproof housing which makes it suitable for measurements even under harsh field conditions. Preliminary tests on stability and accuracy were carried out during two two-week field measurement campaigns, with the three sampling inlets being placed at the same height together with the inlet of a reference instrument. The readings of the three channels agreed well (with correlation coefficients above 0.96). Comparison to reference instruments showed good stability of the photoacoustic instrument, there was no measurable zero-drift or change in sensitivity during the tests. Flux measurements were carried out during a three-week field campaign in southern Scotland over fertilized grassland with reference to a wet-chemical AMANDA instrument in gradient configuration. Ammonia fluxes calculated from the data of the two instruments agreed well. Fluxes up to 2500 ng m^?2 s^?1 were observed after fertilization. The minimum detectable ammonia flux was calculated on the basis of “virtual ammonia fluxes”, from measurements carried out with all inlets at the same height and was found to be ±60 ng m^?2 s^?1 which ensures reliable measurements above intensively managed grasslands or agricultural fields.     

Measurements of air–surface exchange rates of volatile organic compounds

Vertical gradients of volatile organic compounds (VOCs) were measured over a maize field and a soybean field in 1995 and 1996, respectively, in the Lower Coastal Plains of North Carolina. The measurements over the maize field were conducted in its early growth period, during May 1995, and the measurements over the soybean field were conducted in its middle and later growth periods during July through August 1996 at the same location. These measurements were combined with micrometeorological flux measurements to determine emission flux measurements for various VOCs. This measurement programme was part of project NOVA (Natural emissions of Oxidant precursors: Validation of techniques and Assessment) to estimate the flux of VOCs. Methanol was identified as the major biogenic compound for both years with the average flux of 3450 ± 1456 µg/m²/hr over maize and 3079 ± 2766 µg/m²/hr over soybean. Acetone is another compound that was identified as a biogenic compound for both years with the average flux of 425 ± 223 µg/m²/hr over maize and 2701 ± 1710 µg/m²/hr over soybean. In addition to biogenic compounds, a large number of aromatic compounds, including styrene and 1,2,4-trimethylbenzene, were also identified as emissions from the ground over the soybean field.     

Estimation of the exchange of sulphur pollution over the Balkan region in 1995–2000

The Bulgarian dispersion model 'Eulerian Model for Air Pollution' (EMAP) is used to estimate the sulphur pollution over the Balkan region for the period 1995–2000. A subdomain of the European Monitoring and Evaluation Programme (EMEP) grid is chosen containing 12 countries. The computational grid in this domain has a space step of 25 km, twice as fine as the EMEP grid. The former operational DWD 'Europa-Model' is used as meteorological driver. The source input is the official EMEP emission data. Monthly calculations are made having the last moment fields from the previous month as initial conditions for the next one. The boundary conditions are set to zero, so the influence of other European sources is not accounted for in this study. According to the EMEP methodology, multiple runs are made setting every time the sources of various countries to zero. The impact of every country in the pollution of all others is estimated.     

Characteristics of lead geochemistry and the mobility of Pb isotopes in the system of pedogenic rock–pedosphere–irrigated riverwater–cereal–atmosphere from the Yangtze River delta region,China

Knowledge of the characteristics of Pb and its isotopic transfer in different compartments is scant, especially for the mobility of Pb isotopes in the geochemical cycle. The present study characterizes differential Pb transport mechanism and the mobility of Pb isotopes in the pedogenic parent rock–pedosphere–irrigated riverwater–cereal–atmosphere system in the Yangtze River delta region, by determining Pb concentration and Pb isotopic ratios of pedogenic parent rocks, fluvial suspended particle matter, tillage soils, soil profiles, irrigated riverwater, fertilizer, Pb ore, cereal roots and grains. The results show that Pb isotopes in the geochemical cycle generally follow the equation of ²⁰⁸Pb/²⁰⁶Pb = −1.157 × ²⁰⁶Pb/²⁰⁷Pb + 3.46 (r² = 0.941). However, Pb isotopes have different mobility in different environmental matrixes. Whereas in the pedosphere, the heavier Pb (²⁰⁸Pb) usually shows stronger mobility relative to the lighter Pb, and is more likely to transfer into soil exchangeable Pb fraction and carbonates phase. The lighter Pb shows stronger transfer ability from soil to cereal grain via root compared to the heavier Pb. However, the cereal grains have lower ²⁰⁶Pb/²⁰⁷Pb and higher ²⁰⁸Pb/²⁰⁶Pb ratios than root and tillage soil, similar to the airborne Pb and anthropogenic Pb, implying that a considerable amount of Pb in cereal grains comes from the atmosphere. The estimate model shows that 16.7–52.6% (average: 33.5%) of Pb in rice grain is the airborne Pb.     

Concentrations,atmospheric partitioning,and air–water/soil surface exchange of polychlorinated dibenzo-p-dioxin and dibenzofuran along the upper reaches of the Haihe River basin,North China

Polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/PCDF) were overall measured and compared in ambient air, water, soils, and sediments along the upper reaches of the Haihe River of North China, so as to evaluate their concentrations, profiles, and to understand the processes of gas–particle partitioning and air–water/soil exchange. The following results were obtained: (1) The average concentrations (toxic equivalents, TEQs) of 2,3,7,8-PCDD/PCDF in air, water, sediment, and soil samples were 4,855 fg/m³, 9.5 pg/L, 99.2 pg/g dry weight (dw), and 56.4 pg/g (203 fg TEQ/m³, 0.46 pg TEQ/L, 2.2 pg TEQ/g dw, and 1.3 pg TEQ/g, respectively), respectively. (2) Although OCDF, 1,2,3,4,6,7,8-HpCDF, OCDD, and 1,2,3,4,6,7,8-HpCDD were the dominant congeners among four environmental sinks, obvious discrepancies of these congener and homologue patterns of PCDD/PCDF were observed still. (3) Significant linear correlations for PCDD/PCDF were observed between the gas–particle partition coefficient (K _p) and the subcooled liquid vapor pressure (P _L ⁰) and octanol–air partition coefficient (K _oa). (4) Fugacity fraction values of air–water exchange indicated that most of PCDD/PCDF homologues were dominated by net volatilization from water into air. The low-chlorinated PCDD/PCDF (tetra- to hexa-) presented a strong net volatilization from the soil into air, while high-chlorinated PCDD/PCDF (hepta- to octa-) were mainly close to equilibrium for air–soil exchange.     

Modeling and optimization of trihalomethanes formation potential of surface water (a drinking water source) using Box–Behnken design

Purpose  

The present research aims to investigate the individual and interactive effects of chlorine dose/dissolved organic carbon ratio, pH, temperature, bromide concentration, and reaction time on trihalomethanes (THMs) formation in surface water (a drinking water source) during disinfection by chlorination in a prototype laboratory-scale simulation and to develop a model for the prediction and optimization of THMs levels in chlorinated water for their effective control.     

Sampling of carbonaceous particles in the atmosphere—II

A laboratory study was conducted to test the ability of various sorbents to remove vapor-phase atmospheric carbonaceous materials otherwise retained by sorption on quartz filters, a ‘positive artifact’ in sampling atmospheric particulate C. A dual quartz filter strategy, in which the C recovered from the after-filter is used to correct for the positive artifact, was also assessed. Sorbents such as activated Al₂O₃ and quartz fiber can reduce by up to 60% the positive artifact in sampling at 20 ℓ min⁻ with 47-mm Pallflex 2500 QAO quartz filters. On the assumption, defended herein, that a quartz fiber profilier was unlikely to influence the ratio of C retained by sorption on downstream tandem quartz filters, the dual filter strategy permitted correction for this positive artifact within, on average, 12%. Conclusions from an initial study suggesting extensive loss by volatilization of previously collected particulate C are reassessed.     

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.     

Comparison of micrometeorological and two-film estimates of air–water gas exchange for alpha-hexachlorocyclohexane in the Canadian archipelago

The air-sea gas exchange of alpha-hexachlorocyclohexane (α-HCH) in the Canadian Arctic was estimated using a micrometeorological approach and the commonly used Whitman two-film model. Concurrent shipboard measurements of α-HCH in air at two heights (1 and 15 m) and in surface seawater were conducted during the Circumpolar Flaw Lead study in 2008. Sampling was carried out during eight events in the early summer time when open water was encountered. The micrometeorological technique employed the vertical gradient in air concentration and the wind speed to estimate the flux; results were corrected for atmospheric stability using the Monin-Obukhov stability parameter. The Whitman two-film model used the concentrations of α-HCH in surface seawater, in bulk air at 1 and 15 m above the surface, and the Henry's law constant adjusted for temperature and salinity to derive the flux. Both approaches showed that the overall net flux of α-HCH was from water to air. Mean fluxes calculated using the micrometeorological technique ranged from -3.5 to 18 ng m(-2) day(-1) (mean 7.4), compared to 3.5 to 14 ng m(-2) day(-1) (mean 7.5) using the Whitman two-film model. Flux estimates for individual events agreed in direction and within a factor of two in magnitude for six of eight events. For two events, fluxes estimated by micrometeorology were zero or negative, while fluxes estimated with the two-film model were positive, and the reasons for these discrepancies are unclear. Improvements are needed to shorten air sampling times to ensure that stationarity of meteorological conditions is not compromised over the measurement periods. The micrometeorological technique could be particularly useful to estimate fluxes of organic chemicals over water in situations where no water samples are available.     

Releases of anhydrous ammonia from pressurized containers — the importance of denser-than-air mixtures

The purpose of this paper is to examine the behaviour of ammonia vapour which has escaped to the atmosphere as a result of the accidental failure of a pressurized container. It is shown that the circumstances of the release are such that the formation of a cold ammonia air mixture, which is denser than the surrounding air, is likely. As a result, gravity driven phenomena must be taken into account; the cloud slumps and becomes very broad. It is shown that this slumping is insensitive to assumptions made about the rate of entrainment of the air and about the rate at which the mixture is heated by the ground. It is also demonstrated that, unless the windspeed is exceedingly low, the dispersing ammonia may not become buoyant; this is another phenomenon that is insensitive to parameter variations.A section of the paper is devoted to a critical examination of the uncertainties which must be overcome before a complete model of the escape of ammonia from a pressurized container can be written down. It is argued, however, that the characteristic features described above are not sensitive to these uncertainties. Finally, a simple model is used to describe the behaviour of a 20 Te “puff” of ammonia and the results are compared with accounts of accidental escapes of about that size. It is demonstrated that agreement with such facts as can be established is satisfactory.     

The photochemical formation and gas–particle partitioning of oxidation products of decamethyl cyclopentasiloxane and decamethyl tetrasiloxane in the atmosphere

Decamethyl cyclopentasiloxane (D₅) and decamethyl tetrasiloxane (MD₂M) were injected into a smog chamber containing fine Arizona road dust particles (95% surface area <2.6 μM) and an urban smog atmosphere in the daytime. A photochemical reaction – gas–particle partitioning reaction scheme, was implemented to simulate the formation and gas–particle partitioning of hydroxyl oxidation products of D₅ and MD₂M. This scheme incorporated the reactions of D₅ and MD₂M into an existing urban smog chemical mechanism carbon bond IV and partitioned the products between gas and particle phase by treating gas–particle partitioning as a kinetic process and specifying an uptake and off-gassing rate. A photochemical model PKSS was used to simulate this set of reactions. A Langmuirian partitioning model was used to convert the measured and estimated mass-based partitioning coefficients (K_P) to a molar or volume-based form. The model simulations indicated that >99% of all product silanol formed in the gas-phase partition immediately to particle phase and the experimental data agreed with model predictions. One product, D₄TOH was observed and confirmed for the D₅ reaction and this system was modeled successfully. Experimental data was inadequate for MD₂M reaction products and it is likely that more than one product formed. The model set up a framework into which more reaction and partitioning steps can be easily added.     

The chemistry of carbonyl compounds in the atmosphere—A review

Carbonyl compounds are very important for the trophospheric physico-chemistry because they are the result of the first photo-oxidation stage of almost all organic compounds and they are the essential originators of the free radicals. In the present review we make a synthesis of the studies on the carbonyl compounds chemistry in the trophosphere by successively examining: measurement methods in the trophosphere, sources of primary carbonyl compounds, formation of secondary carbonyl compounds in the atmosphere, reactivity of carbonyl compounds in the atmosphere.     

Food contamination by C20–C50 mineral paraffins from the atmosphere

Most foods from plant origin usually contain 1–10 mg/kg (dry weight) of non-resolved isomeric alkanes in the range of the n-alkanes C₂₀–C₅₀ which are assumed to be residues from mineral oil products (in addition to the natural paraffins). In edible vegetable oils, concentrations may exceed 100 mg/kg. Since it was suspected that this contamination was mostly of environmental origin, particulate matter from air was analysed for the same range of paraffins. In a road tunnel, around 5 μg/m³ of such paraffins were found, corresponding to about 3% of the fine dust (PM10). The composition corresponded to that found in the particulate matter from the exhaust of diesel engines, which in turn largely corresponded to engine (lubricating) oil. In Swiss cities, the C₂₀–C₅₀ mineral paraffins in the PM10 from ambient air amounted to 0.1–1.5 μg/m³ (about 1% of the dust) and seemed to primarily originate from incomplete combustion of heating and diesel oil, lubricating oil, and road tar debris. On the countryside, the concentrations were around 0.03 μg/m³ (0.3% of the dust). Soil contained 0.5–10 mg/kg of these paraffins. The similarity of the molecular weight (volatility) distribution suggests that the food contamination with paraffins, is mostly from the air. A substantial proportion probably consists of lubricating oil. If this hypothesis is confirmed, measures should be investigated to reduce this contamination.     

Sulphates and sulphuric acid in the atmosphere in the years 1971–1976 in The Netherlands

In 1971 an orientating study was started concerning the ground-level concentrations of sulphate and sulphuric acid relative to sulphur dioxide. In order to achieve a more selective method for the determination of sulphuric acid, the separation of sulphuric acid from sulphates by isopropanol was used. After separation sulphuric acid and sulphate are determined spectrophotometrically with barium chloranilate. Air samples were taken with air samplers using 0.8 μm pore cellulose triacetate filters. In the winter 1971–1972 at Arnhem the ratio sulphate/total sulphur correlated significantly with the relative humidity and decreased with increasing SO₂ concentration. The mean value of the ratio was 12.5% at a mean SO₂ concentration of 71 μg m⁻³. The mean ratio H₂SO₄/total sulphur was 0.34%. In summer 1972, with a mean ratio sulphate/total sulphur of 36.8% at a mean SO₂ level of 8 μg m⁻³, there was a correlation between sulphate and NH₃ on days with a relative humidity >80%; this suggests an influence on the oxidation rate by NH₃. The amounts of NH₄⁺, SO₄²⁻, and NO₃⁻ give rise to the supposition that the greater part of sulphate and nitrate is present as ammonium salts. The measurements were continued at Arnhem and Rotterdam (Rijnmond area) in 1973, 1975 and 1976. In these years there was a strong decrease in SO₂ concentration with a less stronger decrease in sulphate concentration. This together with the uniform distribution of sulphates in The Netherlands indicates that the sulphate level is caused mainly by long range transport. There was no increased reactivity in the formation of sulphates in the industrial Rijnmond area as compared to the eastern part of The Netherlands. Increased H₂SO₄ concentrations occurred as a result of transport of aerosols over sea by western winds. In summer 1976 there were significant correlations between both sulphate and nitrate with ozone at all the measuring stations, from which the existence of photochemical reactions over large areas can be concluded.     

A study of the particulate matter PM10 composition in the atmosphere of Chillán, Chile

Inhalable particulate matter (PM10) concentrations were measured over 24-h intervals at six different urban sites in the city of Chillán from September 2001 to April 2003. Sampling locations were selected to represent central city, commercial, residential, and industrial portions of the city. Chemical composition of PM10 was performed to samples of 47 mm diameter Teflon membranes within the city of Chillán. The spatial and temporal variability of the chemical composition of PM10 was evaluated taking into account additional data from meteorology and further air pollutants. The majority of PM mass was comprised of carbon, nitrate, sulfate, ammonium, and crustal components but in different proportion on different days and at different sites. The chemical analyses showed that carbonaceous substances and crustal material were the most abundant component of PM10 during the winter and summer, respectively. The concentrations of PM10 were higher during the cold season than during the warm season. The PM10 concentrations were higher in the downtown area of the city of Chillán, where also the chemical composition was more variable due to urban traffic and other anthropogenic sources.     

Preparation and evaluation of Pd-Sn modified Ru-Ir electrode for denitrification of high chlorine ammonia–nitrogen wastewater

Environmental Science and Pollution Research - In this paper, Pd-Sn modified Ru-Ir electrode was prepared by thermal oxidation method, and the effects of doping amount of Pd-Sn and synthesis...     

A lagrangian approach to analyse the tropospheric ozone climatology in the tropics: Climatology of stratosphere–troposphere exchange at Reunion Island

Sixteen years of ozone measurements (1992–2006) at Reunion Island (21°S, 55.5°E) have been processed to detect stratospheric signatures on each single ozone profile.The characterisation method consists in the advection of the potential vorticity (PV) over two to ten days of backtrajectory with the lagrangian trajectory code LACYTRAJ. LACYTRAJ is a Trajectory-Reverse Domain Filling code using the ERA40 ECMWF database and allowing the reconstruction of high resolution advected PV profiles. Correlation between high values of ozone mixing ratio and high PV is interpreted as a stratospheric signature.A climatology of STE events at Reunion has been derived and reveals that STE events occur more frequently during spring (SON) and summer (DJF). The method is tested for a set of PV threshold values (i.e. 1 PVU, 1.5 PVU and 2 PVU) and for a set of duration of backtrajectories (i.e. 2 days, 5 days and 10 days). The number of detected STE is sensitive to PV threshold values and duration criterions. For instance, the number of stratospheric intrusions detected in October with a 1.5 PVU criterion ranges between 25% (2 days of backtrajectories) and 56% (10 days of backtrajectories). The vertical distributions of STE show intrusions covering the whole free troposphere (between 7 and 15 km) and mainly located in the upper troposphere.Finally, results show that an important number of stratospheric intrusions are detected during spring and in the upper troposphere what points at the contribution of the stratospheric source to the tropospheric ozone spring maximum which is strongly influenced by the biomass burning emissions from South Africa and Madagascar.     

Removal of ammonia nitrogen from water by mesoporous carbon electrode–based membrane capacitance deionization

Environmental Science and Pollution Research - The removal of ammonia nitrogen from wastewater is always a focus in current water treatment. In this study, a combination of mesoporous carbon...