Chemical composition of dew in Amman, Jordan

Twenty-six dew samples were collected on a glass surface from an urbanized area in Amman city during the period October 1999 to June 2000. They were analyzed for the major ions (Cl, SO₄, NO₃, Ca, Mg, Na, K and NH₄) in addition to three heavy metals (Pb, Cd and Co). Rain samples were collected for the same period and compared to the chemical constituents of dew.It was found that both rain and dew samples were of almost neutral acidity due to the buffering effect of CaCO₃. Dew composition was mainly from CaSO₄ solution due to conversion of CaCO₃ to CaSO₄ when left exposed to a sulfate-rich atmosphere. The total dissolved solids were higher in dew than rain samples of the same period. This was attributed to higher evaporation effect on dew than rain.The heavy metal content in dew is highest during the cold winter season (December–March) due to excess fossil fuel combustion for heating purposes in this period. The heavy metal content in dew was lower than that for rain during the same period because of the shorter period of dew formation than rainwater.     

Latitude versus Depth Simulations of Ecodynamics and Dissolved Gas Chemistry Relationships in the Central Pacific

Nutrient ecology and trace gas processing are intimately coupled in the surface ocean and participate in key linkages through the Earth biogeochemical system. We have added water column photochemistry for volatile sulfur and organic compounds to large scale nutrient cycle modules, in order to create a one dimensional, open ocean ecochemistry simulator. Phyto- and zooplankton, recyclers and biological waste products are represented through N and Fe densities. Dimethyl sulfide, carbonyl sulfide and the methyl halides are tracked individually along with certain precursors and nonmethane hydrocarbons. The model is applied along the 180 degree meridian in the Northern Hemisphere. Ecodynamics are validated against satellite ocean color maps. Biological/photochemical production terms are then iterated upon to match measured distributions for the trace gases. Data are most complete for dimethyl sulfide. Major patterns in its climatology are captured within individual ecological provinces. However, at the basin scale reduced sulfur release must be varied over almost an order of magnitude because the mechanism developed contains only one plant taxon. Based on sparser data, first order rate constants are estimated for phytoplanktonic exudation of the methyl halides. Parameters are also established for photolytic injection of carbonyl sulfide and propylene from the dissolved organics. Ocean general circulation models and interactive ocean-atmosphere transport simulations are discussed as frameworks for future application.     

Photochemistry of Cu complexed with chromophoric dissolved organic matter: implications for Cu speciation in rainwater

Significant quenching of fluorescence by Cu in rainwater samples from southeastern North Carolina demonstrates that chromophoric dissolved organic matter (CDOM) is an effective ligand for Cu in rainwater. A strong inverse correlation between the decrease in fluorescence upon Cu addition and CDOM abundance suggests the presence of excess binding sites for Cu in high CDOM samples. Electroanalytical studies indicate that CDOM extracted from C₁₈ cartridges formed Cu complexes with concentrations and conditional stability constants similar to ligands found in ambient rainwater. When authentic rainwater samples were photolyzed with simulated sunlight both photoproduction and photodestruction of ligands were observed, suggesting the photochemical response of Cu-complexing ligands in rainwater is the result of two competing reactions. The rate of CDOM photobleaching was directly related to changes in strong ligands (K_CuL ∼ 10¹⁵) whereas weaker ligands (K_CuL < 10¹³) were not correlated, suggesting the photolabile CDOM resides in the strong ligand class. A photolysis study comparing filtered and unfiltered rainwater samples indicated that Cu-complexing ligands adsorbed onto or otherwise associated with particles are photodegraded much more rapidly than dissolved ligands. Photolysis with UV radiation appears to be most effective at engendering changes in Cu ligands, however a significant photochemical response was also observed when samples were exposed to photosynthetically active radiation with wavelengths greater than 400 nm. Results from this study demonstrate that complexation of Cu by CDOM has important ramifications for controlling both the speciation of the metal and the reactivity of CDOM in rainwater.     

The Gaia Hypothesis: Conjectures and Refutations

The uncertainties surrounding global climate change provide ample evidence, if any were necessary, of the need for a whole-system view of the Earth. Arguably the most visible – and controversial – attempt to understand Earth as a system has been Lovelock's Gaia theory. Gaia has been a fruitful hypothesis generator, and has prompted many intriguing conjectures about how biological processes might contribute to planetary-scale regulation of atmospheric chemistry and climate. In many important cases, however, these conjectures are refuted by the available data. For example, Gaia theory predicts that the composition of the atmosphere should be tightly regulated by biological processes, but rates of carbon uptake into the biosphere have accelerated by only about 2% in response to the 35% rise in atmospheric CO₂ since pre-industrial times. Gaia theory would predict that atmospheric CO₂ should be more sensitively regulated by terrestrial ecosystem uptake (which is biologically mediated) than by ocean uptake (which is primarily abiotic), but both processes are about equally insensitive to atmospheric CO₂ levels. Gaia theory predicts that biological feedbacks should make the Earth system less sensitive to perturbation, but the best available data suggest that the net effect of biologically mediated feedbacks will be to amplify, not reduce, the Earth system's sensitivity to anthropogenic climate change. Gaia theory predicts that biological by-products in the atmosphere should act as planetary climate regulators, but the Vostok ice core indicates that CO₂, CH₄, and dimethyl sulfide – all biological by-products – function to make the Earth warmer when it is warm, and colder when it is cold. Gaia theory predicts that biological feedbacks should regulate Earth's climate over the long term, but peaks in paleotemperature correspond to peaks in paleo-CO₂ in records stretching back to the Permian; thus if CO₂ is biologically regulated as part of a global thermostat, that thermostat has been hooked up backwards for at least the past 300 million years. Gaia theory predicts that organisms alter their environment to their own benefit, but throughout most of the surface ocean (comprising more than half of the globe), nutrient depletion by plankton has almost created a biological desert, and is kept in check only by the nutrient starvation of the plankton themselves. Lastly, where organisms enhance their environment for themselves, they create positive feedback; thus Gaia theory's two central principles – first, that organisms stabilize their environment, and second, that organisms alter their environment in ways that benefit them – are mutually inconsistent with one another. These examples suggest that the further development of Gaia theory will require more deliberate comparison of theory and data.     

Cloud model experiments of the effect of iron and copper on tropospheric ozone under marine and continental conditions

Summary We have used a multi-phase cloud photochemistry model to investigate the influence of dissolved iron (Fe) and copper (Cu) on the in-cloud production and loss of ozone and ozone-related species. Comparison of the results of our simulations with and without Fe and Cu reactions for three different photochemical scenarios (marine, averaged continental and polluted continental) indicate that Fe and Cu reactions, depending upon the scenario considered, can either increase or decrease the predicted rate of loss of ozone and ozone related species. For the marine and averaged continental scenarios the rate of loss of ozone in the aqueous-phase was decreased by as much as 45% and 70%, respectively, when Fe and Cu reactions were considered. For polluted continental conditions, the rate of loss of ozone in the aqueous phase increased with a factor 2 for low metal concentrations up to a factor 20 for high metal concentrations. In all three scenarios inclusion of the Fe and Cu reactions results in cloud droplets becoming more efficient sinks for gas-phase HO₂ and also enhances OH production. The net effect of the decreased losses of ozone from the aqueous phase and the effect of the cloud droplets on HO₂ and OH determine the overall impact on ozone and ozone related species, for each of the situations considered. Overall, when Fe and Cu reactions were included the marine cloud was found to be a less efficient sink for ozone, and averaged continental and polluted continental clouds were more efficient sinks for ozone (O₃ losses doubled in the averaged continental scenario). The higher OH flux in the aqueous phase also enhances the rate at which organic compounds, such as formaldehyde and formic acid, are oxidized in the cloud.With 4 Figures     

Effects of high CO2 levels on surface temperature and atmospheric oxidation state of the early Earth

One-dimensional radiative-convective and photochemical models are used to examine the effects of enhanced CO₂ concentrations on the surface temperature of the early Earth and the composition of the prebiotic atmosphere. Carbon dioxide concentrations of the order of 100–1000 times the present level are required to compensate for an expected solar luminosity decrease of 25–30%, if CO₂ and H₂O were the only greenhouse gases present. The primitive stratosphere was cold and dry, with a maximum H₂O volume mixing ratio of 10^–6. The atmospheric oxidation state was controlled by the balance between volcanic emission of reduced gases, photo-stimulated oxidation of dissolved Fe⁺² in the oceans, escape of hydrogen to space, and rainout of H₂O₂ and H₂CO. At high CO₂ levels, production of hydrogen owing to rainout of H₂O₂ would have kept the H₂ mixing ratio above 2×10^–4 and the ground-level O₂ mixing ratio below 10^–11, even if no other sources of hydrogen were present. Increased solar UV fluxes could have led to small changes in the ground-level mixing ratios of both O₂ and H₂.     

Photooxidation of dimethyl sulfide and dimethyl disulfide. I: Mechanism development

Detailed theoretical (Part I, this article) and experimental (Part II) investigations are presented for the mechanism of the atmospheric photooxidation of dimethyl sulfide (CH₃SCH₃) and dimethyl disulfide (CH₃SSCH₃). In this paper, comprehensive mechanisms for the atmospheric chemistry of CH₃SCH₃ and CH₃SSCH₃ are developed based on fundamental considerations of all available kinetic and mechanistic information.     

Sulfur dioxide and dimethyl sulfide in the central Pacific troposphere

Boundary-layer and free-troposphere measurements of sulfur dioxide, dimethyl sulfide, and carbon disulfide were made during transits of the central and southern Pacific Ocean between Hawaii and Australia. Sulfur dioxide was generally less than 100 pptv and highly variable with no correlation with respect to geographic location or altitude. Dimethyl sulfide in the boundary layer had a concentration range of <10 to 200 pptv. Highest concentrations of DMS were in the equatorial region of the southern hemisphere although the concentrations were dependent on location and meteorological regime. In the region of the Fiji Islands several boundary layer samples had SO₂, DMS, and CS₂. In 1989, additional SO₂ measurements were made between Hawaii and the equator and to the west of Hawaii downwind of the Kilauea volcano plumes.Paper submitted to the 7th International Symposium of the Commission for Atmospheric Chemistry and Global Pollution on the Chemistry of the Global Atmosphere held in Chamrousse, France, from 5 to 11 September 1990.     

Speciation and Photochemistry of Mercury in Rainwater

Mercury speciation was determined in rainwater from 76 storms in southeastern North Carolina between September 1, 2003 and September 30, 2005. Volume-weighted average concentrations of total Hg (THg), total dissolved Hg (TDHg), particulate Hg (Hg_part) and dissolved monomethyl Hg (MMHg) were 45.5 pM, 34.8 pM, 12.0 pM and 1.1 pM respectively. TDHg accounted for 77% of THg in precipitation which is similar to Cu but significantly higher than Cr or Fe. Concentrations of the various Hg species were very similar during summer and winter indicating that there was not a dominant seasonal influence on Hg speciation in rainwater at this location. THg, TDHg, and MMHg concentrations were also not significantly impacted by storm origin suggesting that they are relatively well mixed regionally and that air mass back trajectory is not the dominant factor controlling their concentration at this location. Concentrations of TDHg and Hg_part were inversely correlated in rainwater samples subjected to irradiation with simulated sunlight, suggesting the distribution between dissolved and particulate Hg may be controlled by photochemical transformations. Unlike TDHg and Hg_part, no significant changes in MMHg were observed upon photolysis of rainwater indicating that its distribution is not significantly driven by sunlight-mediated reactions, in contrast to what has been observed in surface waters. Results presented in this study indicate that the speciation of Hg in rainwater is dynamic and is driven by a complex combination of natural and anthropogenic processes as well as interactions with sunlight.     

Modelling of the nighttime nitrogen and sulfur chemistry in size resolved droplets of an orographic cloud

A chemistry module has been incorporated into a Lagrangian type model that computes the dynamics and microphysics of an orographical cloud formed in moist air flowing over the summit of Great Dun Fell (GDF) in England. The cloud droplets grow on a maritime aerosol which is assumed to be an external mixture of sea-salt particles and ammonium-sulfate particles. The dry particle radii are in the range 10 nm<r<1 µm. The gas-phase chemical reaction scheme considers reactions of nitrogen compounds that are important at night. The treatment of scavenging of gases into the aqueous phase in the model takes into account the different solubilities and accommodation coefficients. The chemistry in the aqueous phase focusses on the oxidation of S(IV) via different pathways.Sensitivity analyses have been performed to investigate deviations from gas-liquid equilibria according to Henry's law and also to study the influence of iron and of nitrogen compounds on the aqueous-phase oxidation of dissolved SO₂. When addressing these questions, special attention has been given to the dependence on the droplet size distribution and on the chemical composition of the cloud condensation nuclei on which the droplets have formed. It was found that the oxidation of S(IV) via a chain reaction of sulfur radicals can be important under conditions where H₂O₂ is low. However, major uncertainties remain with respect to the interaction of iron with the radical chain. It was shown that mixing of individual cloud droplets, which are not in equilibrium according to Henry's law, can result in a bulk sample in equilibrium with the ambient air. The dependence of the aqueous-phase concentrations on the size of the cloud droplets is discussed for iron, chloride and NO₃.     

A Laboratory and Theoretical Study on the Uptake of SO2 Gas by Large and Small Water Drops Containing Heavy Metal Ions

Laboratory experiments have been carried out to investigate the uptake of sulfur dioxide by water drops containing heavy metal ions where the metal ions serve as catalysts to oxidise the taken up S(IV) into S(VI). During the gas uptake the drops were freely suspended at their terminal velocity in the airstream of the Mainz vertical wind tunnel. Two series of experiments were carried out, one with large millimeter size water drops containing manganese or iron ions, and the other with small water drops containing manganese ions and having radii in hundreds of micron size range. The experimental results were compared against model computations using the Kronig–Brink model and the fully mixed model, modified for the case that heavy metal ions present in the liquid phase act as catalysts for the oxidising process. The results of the model calculations show that there are only small differences between the predicted gas uptake according to the two models. In addition it was found that the experimental obtained results from the uptake of SO₂ by water drops containing heavy metal ions for both, large and small water drops did agree with the model results.     

DMS and SO2 at Baring Head, New Zealand: Implications for the Yield of SO2 from DMS

Atmospheric dimethyl sulfide (DMS) and sulfur dioxide (SO₂) concentrations were measured at Baring Head, New Zealandduring February and March 2000. Anti-correlated DMS and SO₂ diurnalcycles, consistent with the photochemical production of SO₂ from DMS, were observed in clean southerly air off the ocean. The data is used to infer a yield of SO₂ from DMS oxidation. The estimated yields are highly dependent on assumptions about the DMS oxidation rate. Fitting the measured data in a photochemical box model using model-generated OH levels and the Hynes et al. (1986) DMS + OH rate constant suggests that theSO₂ yield is 50–100%, similar to current estimates for the tropical Pacific.However, the observed amplitude of the DMS diurnal cycle suggests that the oxidation rate is higher than that used by the model, and therefore, that theSO₂ yield is lower in the range of 20–40%.     

Bottom sediments and their role in surface water pollution with mercury (with a special reference to the Northern Dvina River Mouth and the Dvina Bay of the White Sea)

Mercury content in bottom estuarine sediments of the Northern Dvina River and the Dvina Bay of the White Sea is studied. Major regularities of the behavior of the metal and its compounds in bottom sediments of the water area are defined. The role of lithological composition, pH and Eh of the environment, the presence of hydrogen sulfide for determining the content and forms of the mercury presence in the bottom sediments of the region are studied. The sediments related to technogenic formations are specified. The paths and forms of mercury coming from bottom sediments to the near-bottom water level are detected, and the methylmercury content in the sediments is calculated.     

Grab sampling for the determination of sulfur dioxide and dimethyl sulfide in air by isotope dilution gas chromatography/mass spectrometry

Developments allowing the direct determination of sulfur dioxide and dimethyl sulfide in grab samples by gas chromatography/mass spectrometry with isotopically labeled standards (GC/MS/ILS) are reported. Isotopomers of DMS and SO₂ are used as internal standards. Spiked air samples are dried to a dew point of <–60 °C and trapped cryogenically in loops of Teflon tubing. Sealed samples are transported to the laboratory under liquid nitrogen and later subjected to GC/MS analysis. Holding times of up to one month do not result in significant sample loss. For samples collected in a clean marine environment, concentrations of SO₂ and DMS greater than 5 and 8 pptv, respectively, are significantly different from blanks at the 95% confidence level. Average measurement precision derived from a propagation of errors are 9% for SO₂ and 42% for DMS at concentrations from 5–15 pptv.Improvements are outlined which should provide sensitivity and precision comparable to that of on-site GC/MS. The technique will allow increased flexibility for the determination of trace sulfur species in the field under conditions where deployment of a mass spectrometer is not possible.     

A Three-Dimensional Global Model Study of Carbonyl Sulfide in the Troposphere and the Lower Stratosphere

Global distributions of carbonyl sulfide and carbon disulfide have been calculated with a three-dimensional global model of the atmospheric general circulation (ECHAM). The model calculates a global sink strength for carbonyl sulfide of 0.3 Tg S yr^-1, with vegetation uptake being the largest sink. With this sink strength, the sources have to be close to the lower limit of the present estimate in the literature. The calculated mixing ratios are higher in the Southern Hemisphere than in the Northern Hemisphere. This interhemispheric gradient is the opposite of what is observed demonstrating that the present knowledge of the distribution of sinks and sources is not fully adequate. The model calculations support the idea that the open oceans could act as a net sink of carbonyl sulfide. The calculated stratospheric photolysis of carbonyl sulfide constitutes about 4% of the total sink of carbonyl sulfide. A stratospheric production of sulfate from carbonyl sulfide of 0.013 Tg S yr^-1 is obtained, which is 3 to 12 times less than what is needed to maintain the stratospheric sulfate aerosol layer. Although these results are associated with uncertainties, due to the low upper boundary and coarse vertical resolution of the model, they support recent findings of a low stratospheric production of sulfate from carbonyl sulfide. Instead, sulfur dioxide transported from the troposphere is calculated to be the most important precursor for the stratospheric sulfate aerosol layer.     

Influx of dissolved chemical substances to the Ob-Taz estuarine area

The results of calculation and analysis of a long-term spatial variability in volumes of the influx of a wide spectrum of dissolved chemical substances to the Ob-Taz estuarine area are under consideration. It is shown that physical transport of mineral nitrogen and phosphorus, silicic acid, petroleum hydrocarbons, phenols, heavy metal compounds down the rivers flowing into the Ob-Taz estuarine area dominates over the processes of their chemical-biological transformation. Therefore, a substantial amount of these compounds enters the estuarine ecosystems, which leads to a substantial transformation of the component composition of their water environment and a greater extent of its pollution. The latter predetermines a possible transition of the Ob-Taz estuarine area state from equilibrium into crisis, and in occasional years, even into critical state.     

Shipboard measurements of atmospheric dimethylsulfide and hydrogen sulfide in the Caribbean and Gulf of Mexico

Simultaneous shipboard measurements of atmospheric dimethylsulfide and hydrogen sulfide were made on three cruises in the Gulf of Mexico and the Caribbean. The cruise tracks include both oligotrophic and coastal waters and the air masses sampled include both remote marine air and air masses heavily influenced by terrestrial or coastal inputs. Using samples from two north-south Caribbean transects which are thought to represent remote subtropical Atlantic air, mean concentrations of DMS and H₂S were found to be 57 pptv (74 ng S m^-3, =29 pptv, n=48) and 8.5 pptv (11 ng S m^-3, =5.3 pptv, n=36), respectively. The ranges of measured concentrations for all samples were 0–800 pptv DMS and 0–260 pptv H₂S. Elevated concentrations were found in coastal regions and over some shallow waters. Statistical analysis reveals slight nighttime maxima in the concentrations of both DMS and H₂S in the remote marine atmosphere. The diurnal nature of the H₂S data is only apparent after correcting the measurements for interference due to carbonyl sulfide. Calculations using the measured ratio of H₂S to DMS in remote marine air suggest that the oxidation of H₂S contributes only about 11% to the excess (non-seasalt) sulfate in the marine boundary layer.     

NMHC in the marine atmosphere: Preliminary results of monitoring at Amsterdam Island

Between January 1984 and May 1987, C₂ to C₅ NMHC concentrations, and Radon-222 activities were measured at Amsterdam Island in the Indian Ocean. A large variability of about one order of magnitude was observed in the NMHC concentrations. Most of the samples were collected under marine influence. Using ethene as a reference compound for marine emissions, it appears that the NMHC/ethene composition of the air and its variability directly reflect the composition of dissolved gases in surface seawater. Only the ethane/ethene ratio presents a significant deviation from this typical composition and this can be attributed to a continental component. At sea level, the reation frequency of OH radicals with the NMHC is similar to that of methane and carbon monoxide. Thus, the contribution of marine NMHC should be taken into account in the modelling of oxidants in remote atmospheres.     

多烟团模式在环境风险评价中的应用

应用多烟团模式,以硫化氢泄漏对大气影响为研究对象,模拟一起典型的突发性环境风险事故。并结合风对硫化氢的影响作用,预测出给定稳定度时,少量硫化氢泄漏所达到的最大落地浓度以及最大落地浓度点的下风向距离。分析表明,在同样的稳定度条件下,风速的不同会导致硫化氢扩散存在很大差异。并且在模拟过程中,少量的危险性气体硫化氢在大气中的扩散没有出现致死浓度,但存在一定的危害范围。因此,相关部门应当给予足够的重视,并对其周边环境以及居民做出相应的应急防范措施。