Greenhouse gas emissions from penguin guanos and ornithogenic soils in coastal Antarctica: Effects of freezing–thawing cycles

In coastal Antarctica, freezing and thawing influence many physical, chemical and biological processes for ice-free tundra ecosystems, including the production of greenhouse gases (GHGs). In this study, penguin guanos and ornithogenic soil cores were collected from four penguin colonies and one seal colony in coastal Antarctica, and experimentally subjected to three freezing–thawing cycles (FTCs) under ambient air and under N₂. We investigated the effects of FTCs on the emissions of three GHGs including nitrous oxide (N₂O), carbon dioxide (CO₂) and methane (CH₄). The GHG emission rates were extremely low in frozen penguin guanos or ornithogenic soils. However, there was a fast increase in the emission rates of three GHGs following thawing. During FTCs, cumulative N₂O emissions from ornithogenic soils were greatly higher than those from penguin guanos under ambient air or under N₂. The highest N₂O cumulative emission of 138.24 μg N₂O–N kg^?1 was observed from seal colony soils. Cumulative CO₂ and CH₄ emissions from penguin guanos were one to three orders of magnitude higher than those from ornithogenic soils. The highest cumulative CO₂ (433.0 mgCO₂–C kg^?1) and CH₄ (2.9 mgCH₄–C kg^?1) emissions occurred in emperor penguin guanos. Penguin guano was a stronger emitter for CH₄ and CO₂ while ornithogenic soil was a stronger emitter for N₂O during FTCs. CO₂ and CH₄ fluxes had a correlation with total organic carbon (TOC) and soil/guano moisture (M_c) in penguin guanos and ornithogenic soils. The specific CO₂–C production rate (CO₂–C/TOC) indicated that the bioavailability of TOC was markedly larger in penguin guanos than in ornithogenic soils during FTCs. This study showed that FTC-released organic C and N from sea animal excreta may play a significant role in FTC-related GHG emissions, which may account for a large proportion of annual fluxes from tundra ecosystems in coastal Antarctica.     

Laboratory studies on the uptake of aromatic hydrocarbons by ice crystals during vapor depositional crystal growth

Uptake of aromatic hydrocarbons (AH) by ice crystals during vapor deposit growth was investigated in a walk-in cold chamber at temperatures of 242, 251, and 260 K, respectively. Ice crystals were grown from ambient air in the presence of gaseous AH namely: benzene (C₆H₆), toluene (methylbenzene, C₇H₈), the C₈H₁₀ isomers ethylbenzene, o-, m-, p-xylene (dimethylbenzenes), the C₉H₁₂ isomers n-propylbenzene, 4-ethyltoluene, 1,3,5-trimethylbenzene (1,3,5-TMB), 1,2,4-trimethylbenzene (1,2,4-TMB), 1,2,3-trimethylbenzene (1,2,3-TMB), and the C₁₀H₁₄ compound tert.-butylbenzene. Gas-phase concentrations calculated at 295 K were 10.3–20.8 μg m⁻³. Uptake of AH was detected by analyzing vapor deposited ice with a very sensitive method composed of solid-phase micro-extraction (SPME), followed by gas chromatography/mass spectrometry (GC/MS).Ice crystal size was lower than 1 cm. At water vapor extents of 5.8, 6.0 and 8.1 g m⁻³, ice crystal shape changed with decreasing temperatures from a column at a temperature of 260 K, to a plate at 251 K, and to a dendrite at 242 K. Experimentally observed ice growth rates were between 3.3 and 13.3×10⁻³ g s⁻¹ m⁻² and decreased at lower temperatures and lower value of water vapor concentration. Predicted growth rates were mostly slightly higher.Benzene, toluene, ethylbenzene, and xylenes (BTEX) were not detected in ice above their detection limits (DLs) of 25 pg g_ice⁻¹ (toluene, ethylbenzene, xylenes) and 125 pg g_ice⁻¹ (benzene) over the entire temperature range. Median concentrations of n-propylbenzene, 4-ethyltoluene, 1,3,5-TMB, tert.-butylbenzene, 1,2,4-TMB, and 1,2,3-TMB were between 4 and 176 pg g_ice⁻¹ at gas concentrations of 10.3–10.7 μg m⁻³ calculated at 295 K. Uptake coefficients (K) defined as the product of concentration of AH in ice and density of ice related to the product of their concentration in the gas phase and ice mass varied between 0.40 and 10.23. K increased with decreasing temperatures. Values of Gibbs energy (ΔG) were between −4.5 and 2.4 kJ mol⁻¹ and decreased as temperatures were lowered. From the uptake experiments, the uptake enthalpy (ΔH) could be determined between −70.6 and −33.9 kJ mol⁻¹. The uptake entropy (ΔS) was between −281.3 and −126.8 J mol⁻¹ K⁻¹. Values of ΔH and ΔS were rather similar for 4-ethlytoluene, 1,3,5-TMB and tert.-butylbenzene, whereas 1,2,3-TMB showed much higher values.     

Photocatalytic pre-treatment with food-grade TiO2 increases the bioavailability and bioremediation potential of weathered oil from the Deepwater Horizon oil spill in the Gulf of Mexico

Using the 2010 Deepwater Horizon oil spill in the Gulf of Mexico as an impetus, we explored the potential for TiO₂-mediated photocatalytic reactive oxygen species (ROS) generation to increase the bioavailability (solubility) and biodegradability of weathered oil after a spill. Food grade TiO₂, which is FDA approved for use as food additive in the United States, was tested as a photocatalyst for this novel application. Photocatalytic pre-treatment (0.05 wt.% TiO₂, UV irradiation 18 W m^?2, 350–400 nm) for 24 h in a bench top photoreactor increased the soluble organic carbon content of weathered oil by 60%, and enhanced its subsequent biodegradation (measured as O₂ consumption in a respirometer) by 37%. Photocatalytic pre-treatment was also tested outdoors under sunlight illumination, but no significant increase in solubility or biodegradation was observed after 11 d of exposure. Although sunlight irradiation of food-grade TiO₂ generated ROS (assessed by the degradation of 4-chlorophenol as a probe compound), the efficacy of weathered oil pre-treatment was apparently hindered by sinking of the photocatalysts under quiescent conditions and illumination occlusion by the oil. Overall, results indicate that photocatalytic pre-treatment to stimulate bioremediation of weathered oil deserves further consideration, but controlling the buoyancy and surface hydrophobicity of the photocatalysts will be important for future efforts to enable ROS generation in proximity to the target compounds.     

Wet deposition of low molecular weight mono- and di-carboxylic acids,aldehydes and inorganic species in Los Angeles

About 60 rainwater samples were collected at west Los Angeles, California in 1981–1984 and were analyzed for C₁–C₉ monocarboxylic acids (0.33–79 μM, average (av.) 13±15 μM), C₂–C₁₀ dicarboxylic acids (2.9–51 μM, av. 7.5±14 μM) and C₁–C₄ aldehydes (0.85–28 μM, av. 9.2±11 μM). Distributions of monocarboxylic acids show a predominance of formic (average concentration: 6.5 μM) and acetic (av. 5.6 μM) acids followed by propionic acid (av. 0.44 μM). Oxalic acid is the dominant diacid (av. 3.9 μM) followed by succinic acid (av. 1.0 μM). Formaldehyde (av. 6.9 μM) is the dominant aldehyde, with the next most abundant, acetaldehyde, being minor (av. 0.65 μM). For select rain samples described in this paper, were found to comprise monocarboxylic acids 0.9–12.3% (av. 4.4±3.4%), diacids comprise 1.2–9.5% (av. 4.2±3.3%) and aldehydes comprise 0.2–6.2% (av. 2.1±2.2%) of total organic carbon (TOC, 2.0–18.6 mg C l⁻¹; av. 9.8±5.4 mg C l⁻¹). Annual rain fluxes of monocarboxylic acids and aldehydes during 1982–1983 were calculated to be 0.24 and 0.11 g m⁻² yr⁻¹, respectively, with an annual estimated wet deposition in the Los Angeles Basin of 3120 and 1430 tons, respectively. These fluxes are equivalent to 2500 times of the acids and 2.5 times of the aldehydes emitted from automobile exhausts in the Los Angeles air basin. This comparison suggests that major portions of the carboxylic acids detected in the rain are not directly emitted from auto-exhausts, but are most likely produced in the atmosphere by gaseous and/or aqueous phase photo-induced reactions.     

A simple urban dispersion model tested with tracer data from Oklahoma City and Manhattan

A simple urban dispersion model is tested that is based on the Gaussian plume model and modifications to the Briggs urban dispersion curves. An initial dispersion coefficient (σ_o) of 40 m is assumed to apply in built-up downtown areas, and the stability is assumed to be slightly unstable during the day and slightly stable during the night. Observations from tracer experiments during the Joint Urban 2003 (JU2003) field study in Oklahoma City and the Madison Square Garden 2005 (MSG05) field study in Manhattan are used for model testing. The tracer SF₆ was released during JU2003 near ground level in the downtown area and concentrations were observed at over 100 locations within 4 km from the source. Six perfluorocarbon tracer (PFT) gases were released near ground level during MSG05 and sampled by about 20 samplers at the surface and on building roofs. The evaluations compare concentrations normalized by source release rate, C/Q, for each sampler location and each tracer release, where data were used only if both the observed and predicted concentrations exceeded threshold levels. At JU2003, for all samplers and release times, the fractional mean bias (FB) is about 0.2 during the day (20% mean underprediction) and 0.0 during the night. About 45 –50% of the predictions are within a factor of two (FAC2) of the observations day and night at JU2003. The maximum observed C/Q is about two times the maximum predicted C/Q both day and night. At MSG05, for all PFTs, surface samplers, and release times, FB is 0.14 and FAC2 is about 45%. The overall 60 min-averaged maximum C/Q is underpredicted by about 40% for the surface samplers and is overpredicted by about 25% for the building-roof samplers.     

Biomass consumption and CO2, CO and main hydrocarbon gas emissions in an Amazonian forest clearing fire

Biomass consumption and CO₂, CO and hydrocarbon gas emissions in an Amazonian forest clearing fire are presented and discussed. The experiment was conducted in the arc of deforestation, near the city of Alta Floresta, state of Mato Grosso, Brazil. The average carbon content of dry biomass was 48% and the estimated average moisture content of fresh biomass was 42% on wet weight basis. The fresh biomass and the amount of carbon on the ground before burning were estimated as 528 t ha^?1 and 147 t ha^?1, respectively. The overall biomass consumption for the experiment was estimated as 23.9%. A series of experiment in the same region resulted in average efficiency of 40% for areas of same size and 50% for larger areas. The lower efficiency obtained in the burn reported here occurred possibly due to rain before the experiment. Excess mixing ratios were measured for CO₂, CO, CH₄, C₂–C₃ aliphatic hydrocarbons, and PM_2.5. Excess mixing ratios of CH₄ and C₂–C₃ hydrocarbons were linearly correlated with those of CO. The average emission factors of CO₂, CO, CH₄, NMHC, and PM_2.5 were 1,599, 111.3, 9.2, 5.6, and 4.8 g kg^?1 of burned dry biomass, respectively. One hectare of burned forest released about 117,000 kg of CO₂, 8100 kg of CO, 675 kg of CH₄, 407 kg of NMHC and 354 kg of PM_2.5.     

Application of a Lagrangian particle model to assess the impact of harbour,industrial and urban activities on air quality in the Taranto area,Italy

This paper evaluates the relative impact on air quality of harbour emissions, with respect to other emission sources located in the same area. The impact assessment study was conducted in the city of Taranto, Italy. This area was considered as representative of a typical Mediterranean harbour region, where shipping, industries and urban activities co-exist at a short distance, producing an ideal case to study the interaction among these different sources. Chemical and meteorological field campaigns were carried out to provide data to this study. An emission inventory has been developed taking into account industrial sources, traffic, domestic heating, fugitive and harbour emissions. A 3D Lagrangian particle dispersion model (SPRAY) has then been applied to the study area using reconstructed meteorological fields calculated by the diagnostic meteorological model MINERVE. 3D short term hourly concentrations have been computed for both all and specific sources. Industrial activities are found to be the main contributor to SO₂. Industry and traffic emissions are mainly responsible for NO_x simulated concentrations. CO concentrations are found to be mainly related to traffic emissions, while primary PM₁₀ simulated concentrations tend to be linked to industrial and fugitive emissions. Contributions of harbour activities to the seasonal average concentrations of SO₂ and NO_x are predicted to be up to 5 and 30 μg m⁻³, respectively to be compared to a overall peak values of 60 μg m⁻³ for SO₂ and 70 μg m⁻³ for NO_x. At selected urban monitoring stations, SO₂ and NO_x average source contributions are predicted to be both of about 9% from harbour activities, while 87% and 41% respectively of total concentrations are predicted to be of industrial origin.     

Effects of aqueous stable fullerene nanocrystals (nC60) on Daphnia magna: Evaluation of sub-lethal reproductive responses and accumulation

Concerns exist regarding the inadvertent release of engineered nanomaterials into natural systems, and the possible negative ecosystem response that may occur. Understanding sub-lethal effects may be particularly important to determining ecosystem responses as current levels of nanomaterial release are low compared to levels projected for the future. In this work, the sub-lethal effects and bioaccumulation of water stable, nanocrystalline fullerenes as C₆₀, (termed nC₆₀) were studied in Daphnia magna, a globally distributed, parthenogenetic zooplankton. Sub-lethal concentrations were first determined for both mature mother (LD₅₀ = 0.4 mg L⁻¹) and neonate (gestating) daphnids (0.2 mg L⁻¹) in standard 48 h exposure tests. Subsequent experiments focused on the accumulation and effects (at temperatures of 18–28 °C) of nC₆₀, during the D. magna reproductive cycle. The results demonstrate that upon sub-lethal exposure, the mortality rates of gestating daphnids increased with time and developmental stage. The maturation of daughter daphnids was negatively impacted. The mother daphnids were unable to reproduce again after exposure during pregnancy, and differential bioaccumulation occurred as a function of lipid content in the daphnia with the highest accumulation level of 7000 mg kg⁻¹ wet weight. Taken together, these results not only describe the accumulation and sub-lethal effects of nC₆₀ on exposed daphnia, but also highlight the importance of sub-lethal exposure scenarios, which are critical to fully understanding the potential impact of fullerenes and other engineered nanoscale materials on natural systems.     

Regional dispersion of oxidized sulfur in Central Chile

Chile has a long tradition of exploiting mineral resources, particularly copper (Cu). One of the largest Cu smelters, Caletones, located some 150 km south of the country's capital, Santiago, in Central Chile, is responsible for about 0.4% of about 70 Tg S/yr oxidized sulfur (SO_x) emitted by anthropogenic sources worldwide. Santiago, a megacity with 5 million inhabitants, stands for about 5 Gg S/yr. The average meteorological conditions are unfavorable for the dispersion of pollutants in this area. All this poses risks for human health and vegetation. Also, downwind from these polluted areas there may be large-scale impacts on cloud properties and on oxidative cycles. Here, we present the first attempt to assess the regional distribution of SO_x in Central Chile using a dispersion model (MATCH) driven with data from a limited area weather forecast model (HIRLAM). Emphasis has been given to the impact of Cu smelters upon urban air quality, particularly that of Santiago. Six 1-month long periods were simulated for the years 1997, 1998 and 1999. These periods span over a broad range of typical meteorological conditions in the area including El Niño and La Niña years. Estimates of the regional dispersion and deposition patterns were calculated. The emissions from the large Cu smelters dominate the distribution of SO_x. A budget of SO_x over an area of 200×200 km² around Santiago is presented. There is too low a number of monitoring stations to perform a detailed evaluation of MATCH. Nevertheless, the model reproduces consistently all the regional-scale characteristics that can be derived from the available observations.     

Seasonal characteristics of ambient volatile organic compounds in Seoul,Korea

The measurements of C₂–C₉ volatile organic compounds (VOC) were carried out at a site in Seoul, the capital of Korea from August 1998 to July 1999. Air samples were collected for 24 h in 6 l SUMMA canisters every 6 days. The canister samples were quantitatively analyzed by a GC/FID and GC/MS. The species with the highest mean concentration among the 70 identified was propane (7.8 ppb), followed by toluene (6.4 ppb) and ethylene (5.9 ppb). The high concentration of propane was mainly attributed to the emissions by liquefied petroleum gas (LPG) usage for cooking and heating, and butane fuel for transportation. The general trend of the seasonal variation shows higher concentrations in winter and lower ones in summer. This behavior was mainly caused by the variations of temperature, and resultant VOC source strengths, coupled with the variations of the mixing depth. According to the analysis of concentration ratios, the seasonal contributions of the major emission sources to the VOC concentrations were influenced by ambient temperature. Further, it was identified that the contributions by the use of solvents, natural gas, LPG, and butane fuel were closely related to the variations of consumption pattern according to seasons. Through the analysis of the concentration correlations between less reactive compound and highly reactive ones for summer and winter months, it was found that photochemical reactivity affects relative concentration of reactive compound.     

Detection of fullerenes (C60 and C70) in commercial cosmetics

Detection methods are necessary to quantify fullerenes in commercial applications to provide potential exposure levels for future risk assessments of fullerene technologies. The fullerene concentrations of five cosmetic products were evaluated using liquid chromatography with mass spectrometry to separate and specifically detect C₆₀ and C₇₀ from interfering cosmetic substances (e.g., castor oil). A cosmetic formulation was characterized with transmission electron microscopy, which confirmed that polyvinylpyrrolidone encapsulated C₆₀. Liquid-liquid extraction of fullerenes from control samples approached 100% while solid-phase and sonication in toluene extractions yielded recoveries of 27-42%. C₆₀ was detected in four commercial cosmetics ranging from 0.04 to 1.1 μg/g, and C₇₀ was qualitatively detected in two samples. A single-use quantity of cosmetic (0.5 g) may contain up to 0.6 μg of C₆₀, demonstrating a pathway for human exposure. Steady-state modeling of fullerene adsorption to biosolids is used to discuss potential environmental releases from wastewater treatment systems.     

Large-scale aircraft observations of ultra-fine and fine particle concentrations in the remote Siberian troposphere: New particle formation studies

Ultra-fine particle number concentrations were measured over Siberia during two large-scale airborne measurement campaigns in April and September 2006. During both campaigns, an aircraft flew between Novosibirsk and Yakutsk, collecting every 200 km vertical profiles up to 7 km. This dataset was completed by 5 years of monthly profiles above Novosibirsk. Particle number concentration was measured in the size ranges 3–70 and 70–200 nm, along with other tracers. Free troposphere (FT) particle concentrations (N_3–200) varied between 60 and 460 cm^?3, inferior to boundary layer concentrations (100–7000 cm^?3). In April, high concentrations of ～500 cm^?3 were observed in a polluted air mass recently uplifted at 5–6 km altitude over eastern Siberia, with no sign of significant new particle formation. In September, particle concentrations decreased with altitude, but with a steeper gradient in N_70–200 compared to N_3–70, the latter accounting for 90% of the total particle concentration in the free troposphere at 6–7 km altitude. Because ultra-fine particles presumably have short lifetimes, these observed particles could have been formed in situ in the clean Siberian atmosphere. Two cases of possible nucleation with high concentration and N_3–70/N_70–200 ratios are reported for the September campaign, in the upper troposphere and in cloud outflow in the mid-troposphere. In the seasonal analysis, a FT N_3–70 maximum is found in July–August between 6 and 7 km altitude, with N_3–70 accounting for ～90% of N_3–200 supporting the hypothesis of in situ formation in the FT. A secondary FT maximum of N_3–70 was identified later in autumn. In the boundary layer, seasonally maximum N_3–70 concentrations were found over Novosibirsk in May and September, but not in summer, possibly due to scavenging by precipitations and a large condensational sink from biomass burning aerosols. Our dataset has a limited size resolution and no speciation capability; more investigation is thus required to understand the conditions leading to in situ nucleation processes in the Siberian air shed.     

Characterization of n-alkanes in PM2.5 of the Taipei aerosol

Ambient concentrations of n-alkanes with carbon number ranging from 17 to 36 were determined for PM_2.5 samples collected in Taipei city during September 1997–February 1998. The measured concentrations of particulate n-alkanes were in the range of 69–702 ng m⁻³, considerably higher than the concentration levels observed in Los Angeles and Hong Kong. The concentration distributions of n-alkanes homologues obtained in this study exhibited peaks at C₁₉, C₂₄ or C₂₅. This suggests that fossil fuel utilization, such as vehicular exhaust and lubricant residues, was an important contributor to the Taipei aerosol. Source apportionment of PM_2.5 was conducted using carbon preference index (CPI, defined as the ratio of the total concentration of particulate n-alkanes with odd carbon number to that with even carbon number) and U : R ratio (the concentration ratio of unresolved components to resolved components obtained from chromatograms). The low CPI value (0.9–1.9) and high U : R ratio (2.6–6.4) for each sample further confirmed that fossil fuel utilization was the major source of n-alkanes in ambient PM_2.5 of Taipei city. Estimates from these results showed that 69–93% of the n-alkanes in PM_2.5 of the Taipei aerosol originated from vehicular exhaust. The higher concentration level of particulate n-alkanes in the Taipei aerosol was mainly a result of vehicular emissions.     

Trace gas variations at Cape Point,South Africa,during May 1997 following a regional biomass burning episode

During the continuous monitoring of atmospheric parameters at the station Cape Point (34°S, 18°E), a smoke plume originating from a controlled fire of 30-yr-old fynbos was observed on 6 May 1997. For this episode, which was associated with a nocturnal inversion and offshore airflow, atmospheric parameters (solar radiation and meteorological data) were considered and the levels of various trace gases compared with those measured at Cape Point in maritime air. Concentration maxima in the morning of 6 May for CO₂, CO, CH₄ and O₃ amounted to 370.3 ppm, 491 ppb, 1730 ppb and 47 ppb, respectively, whilst the mixing ratios of several halocarbons (F-11, F-12, F-113, CCl₄ and CH₃CCl₃) remained at background levels. In the case of CO, the maritime background level for this period was exceeded by a factor of 9.8. Differences in ozone levels of up to 5 ppb between air intakes at 4 and 30 m above the station (located at 230 m above sea level) indicated stratification of the air advected to Cape Point during the plume event. Aerosols within the smoke plume caused the signal of global solar radiation and UV–A to be attenuated from 52.4 to 13.0 mW cm⁻² and from 2.3 to 1.3 mW cm⁻², respectively, 5 h after the trace gases had reached their maxima. Emission ratios (ERs) calculated for CO and CH₄ relative to CO₂ mixing ratios amounted to 0.042 and 0.0040, respectively, representing one of the first results for fires involving fynbos. The CO ER is somewhat lower than those given in the literature for African savanna fires (average ER=0.048), whilst for CH₄ the ER falls within the range of ERs reported for the flaming (0.0030) and smouldering phases (0.0055) of savanna fires. Non-methane hydrocarbon (NMHC) data obtained from a grab sample collected during the plume event were compared to background levels. The highest ERs (ΔNMHC/ΔCH₄) have been obtained for the C₂–C₃ hydrocarbons (e.g. ethene at 229.3 ppt ppb⁻¹), whilst the C₄–C₇ hydrocarbons were characterised by the lowest ERs (e.g. n-hexane at 1.0 and n-pentane at 0.8 ppt ppb⁻¹).     

Photochemical production and loss of organic acids in high Arctic aerosols during long-range transport and polar sunrise ozone depletion events

Unique daily measurements of water-soluble organics in fine (<2 μm) and coarse (>2 μm) aerosols were conducted at Alert in the Canadian Arctic in winter to spring of 1992. They yield insight into photochemical production and loss of organics during long-range transport and ozone depletion events following polar sunrise. Comprehensive analyses of α, ω-dicarboxylic acids (C₂–C₁₂), ω-oxocarboxylic acids (C₂–C₉) and α-dicarbonyls (C₂, C₃) as well as pyruvic acid and aromatic (phthalic) diacid were conducted using GC and GC/MS techniques. Oxalic (C₂) acid was generally the dominant diacid species in both fine and coarse fractions, followed by malonic (C₃) and succinic (C₄) acids. Concentrations of total diacids in the fine aerosol fraction (0.2–64 ng m⁻³) were 5–60 times higher than those in the coarse fraction (0.01–3 ng m⁻³). After polar sunrise in early-March, the total concentration of fine aerosol diacids increased by a factor of 3–5 while the coarse mode did not change significantly. From dark winter to sunlit spring, temporal changes in correlations and ratios of these water-soluble organics to vanadium and sulfate measured simultaneously suggest that atmospheric diacids and related organic compounds are largely controlled by long-range atmospheric transport of polluted air during winter, but they are significantly affected by photochemical production. The latter can occur in sunlight either during transport to the Arctic or during photochemical events associated with surface ozone depletion and bromine chemistry near Alert in spring. Conversion of gaseous precursors to particulate matter via photochemical oxidation was intensified at polar sunrise, resulting in a peak in the ratio of total diacids to V. During ozone depletion events, complex patterns are indicated in photochemical production and loss depending on the diacid compound. Unsaturated (maleic and phthalic) diacids were inversely correlated with particulate Br whereas saturated diacids (C₂–C₄) positively correlated with particulate Br. These results suggest that Br chemistry associated with ozone depletion leads to degradation of unsaturated diacids and to the production of smaller saturated diacids.     

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.     

Study of the dispersion of VOCs emitted by a municipal solid waste landfill

The dispersion of VOCs emitted by a municipal solid waste landfill was studied for a period of over one year. Sixteen VOCs were monitored: linear alkanes from C₇ to C₁₁, BTEX, trimethylbenzene, trichlorethylene, tetrachlorethylene, α and β-pinenes, limonene. The analytical procedure was first comprised of static long-term sampling of about 2 months using radial diffusion Radiello tubes containing activated carbon, followed by extraction by solvent (i.e. CS₂) and GC/MS analysis. The results were initially analysed on the basis of the total concentration of the quantified VOCs, then by examining the concentrations of certain selected compounds. The influence of different parameters such as operating conditions, meteorological conditions and site morphology was highlighted on the basis of total VOC concentrations. In order to study the VOC's dispersion more closely, 5 compounds were chosen: toluene, benzene, limonene, and the sum trichlorethylene + tetrachlorethylene, as a “marker”, to verify the origin of the VOCs emitted. The results showed that the main source of VOCs is the open cell and lead to different hypotheses on interferences from neighbouring sources and to the proposal of solutions to limit the emission of VOCs and their dispersion. To our knowledge, this type of study has not been accomplished until this day.     

Preparation of controlled nano-MgO and investigation of its bactericidal properties

Nano-MgO is a good bactericide but with strong alkalinity in water due to its rapid hydrolysis. To control its hydrolysis rate and keep its bactericidal properties, we synthesized nano-MgO microspheres using chitosan–alginate system in this study. The synthesized nano-MgO release-controlled microspheres (nMgO-RCM) were with 0.98–1.20 mm of particle sizes. Also, their embedding ratio and loading percentage was 63.52% and 12.27%, respectively. Based on the characterization results, nano-MgO was only observed on surface of the nMgO-RCM. Its release rate from the nMgO-RCM could be controlled by the chitosan–alginate system, and the observed rate constant (k_obs) increased from 0.0289 h⁻¹ to 0.0358 h⁻¹ with the increment of the dosage from 10 mg L⁻¹ to 80 mg L⁻¹. Furthermore, the nMgO-RCM could maintain pH value lower than 8.5 and colony counts less than 20 CFU mL⁻¹ for at least 120 h.     

Winter-grazing reduces methane uptake by soils of a typical semi-arid steppe in Inner Mongolia,China

Steppe ecosystems are regarded as an important sink of atmospheric methane (CH₄) and grazing is hypothesized to reduce CH₄ uptake. However, firm experimental evidence is required to prove this hypothesis. Using a fully automated, chamber-based measuring system, we conducted continuous high-frequency (at a 3-h interval) measurements of CH₄ uptake in a Leymus chinensis steppe, which is a typical grassland ecosystem in Inner Mongolia, China. Two management regimes were investigated: ungrazed since 1999 (UG99) and winter-grazed since 2001 (WG01). Measurements were carried out continuously during the periods of June–September 2004, May–September 2005 and March–June 2006. During all of these periods, significantly lower mean CH₄ uptake (±S.E.) at WG01 (28±0.7 μg C m⁻² h⁻¹) as compared to UG99 (56±1.0 μg C m⁻² h⁻¹) (p<0.01) was found. Total CH₄ uptake during the growing seasons (May–September) 2004 and 2005 at WG01 and UG99 was quantified as 1.15 and 2.15 kg C ha⁻¹, respectively. Annual rates of CH₄ uptake were approximately 1.91 (WG01) and 3.58 kg C ha⁻¹ (UG99), respectively. These results indicate that winter-grazing of steppe significantly reduced atmospheric CH₄ uptake by ca. 47%. The winter-grazing practice may have inhibited CH₄ uptake by (a) increasing the likelihood of physiological water stress for CH₄-consuming bacteria during dry periods, (b) decreasing gas diffusion into the soil and, (c) reducing the populations of CH₄ oxidizing bacteria. These three mechanisms could have collectively or independently facilitated the observed inhibitory effects. Our results suggest that grazing exerts a considerable negative impact on CH₄ uptake in semi-arid steppes at regional scales. Notwithstanding, further studies involving year-round, intensive measurements of CH₄ uptake are needed.     

Temporal and spatial variation of sulfur-gas-transfer between coastal marine sediments and the atmosphere

The spatial and temporal variability of sulfur gas fluxes (H₂S, COS, CH₃SH, DMS, and CS₂) at the sediment–air interface were studied in the intertidal Wadden Sea area of Sylt-Rømø (Germany/Denmark) during eight measuring campaigns between June 1991 and September 1994. Measurements were performed mainly at four sites in a sheltered intertidal bay of approximately 6 km² (Königshafen) and discontinuously in a wider range of the 400 km² Sylt-Rømø tidal flat area. In situ fluxes of the S-gases were determined by a dynamic chamber technique focusing on dry sediment periods. Additional experiments were conducted in order to determine changes in S-gas concentrations in the sediment between the surface and 70 cm depth.In most cases H₂S was the dominant S-gas emitted from the sediment to the atmosphere, contributing up to 70% of the total S-emission at this interface. Mean H₂S emission rates ranged between 0.07 and 9.95 μg S m^-2 h^-1. Both emission rates and relative contribution of H₂S were lowest from fine sand and highest from muddy sites. Diurnal variation of H₂S emission was evident in summer and fall with up to 10-fold higher rates during night than during the day. Distinct seasonal variation of H₂S-transfer between the sediment and the atmosphere was observed with higher emission rates in the summer than in spring or fall. The emission of H₂S to the atmosphere was smaller by a factor of 1600–26 000 than the H₂S produced from sulfate reduction. Apparently, the efficiency by which H₂S produced in the sediment is retained and reoxidized by biogeochemical sediment processes is extremely high. Carbonyl sulfide (COS) was emitted with relatively constant rates in space and time with mean flux rates ranging between 0.24 and 2.0 μg S m^-2 h^-1. Carbon disulfide emission rates were comparable to those of COS and varied between 0.3 and 2.23 μg S m^-2 h^-1. DMS played a minor role in the S-gas transfer from uncovered sediment areas contributing between 3.1 and 23% to total S-emission from the sediment to the atmosphere.