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PubMed2006

Atmospheric chemistry of N-methyl perfluorobutane sulfonamidoethanol, C4F9SO2N(CH3)CH2CH2OH: kinetics and mechanism of reaction with OH.

Relative rate methods were used to measure the gas-phase reaction of N-methyl perfluorobutane sulfonamidoethanol (NMeFBSE) with OH radicals, giving k(OH + NMeFBSE) = (5.8 +/- 0.8) x 10(-12) cm3 molecule(-1) s(-1) in 750 Torr of air diluent at 296 K. The atmospheric lifetime of NMeFBSE is determined by reaction with OH radicals and is approximately 2 days. Degradation products were identified by in situ FTIR spectroscopy and offline GC-MS and LC-MS/MS analysis. The primary carbonyl product C4F9SO2N(CH3)CH2CHO, N-methyl perfluorobutane sulfonamide (C4F9SO2NH(CH3)), perfluorobutanoic acid (C3F7C(O)OH), perfluoropropanoic acid (C2F5C(O)OH), trifluoroacetic acid (CF3C(O)OH), carbonyl fluoride (COF2), and perfluorobutane sulfonic acid (C4F9SO3H) were identified as products. A mechanism involving the addition of OH to the sulfone double bond was proposed to explain the production of perfluorobutane sulfonic acid and perfluorinated carboxylic acids in yields of 1 and 10%, respectively. The gas-phase N-dealkylation product, N-methyl perfluorobutane sulfonamide (NMeFBSA), has an atmospheric lifetime (>20 days) which is much longer than that of the parent compound, NMeFBSE. Accordingly,the production of NMeFBSA exposes a mechanism by which NMeFBSE may contribute to the burden of perfluorinated contamination in remote locations despite its relatively short atmospheric lifetime. Using the atmospheric fate of NMeFBSE as a guide, it appears that anthropogenic production of N-methyl perfluorooctane sulfonamidoethanol (NMeFOSE) contributes to the ubiquity of perfluoroalkyl sulfonate and carboxylate compounds in the environment.

Air Pollutants↗
PubMed2006

Atmospheric lifetime and global warming potential of a perfluoropolyether.

Perfluoropolyethers (PFPEs) are a family of perfluorinated fluids used mainly in industrial applications. Lower molecular weight commercial PFPE fractions have boiling points ranging between 55 and 270 degrees C, and have the potential to escape into the atmosphere. To improve our understanding of the atmospheric chemistry of PFPEs, a distilled fraction of a commercial mixture containing perfluoropolymethylisopropyl ethers (PFPMIEs) was introduced into an atmospheric chamber system. Relative rate techniques were used to determine upper limits for the rate constants for reactions of OH and Cl with PFPMIE in 700 Torr of air at 296 K. The reactivity of PFPMIE with Cl was less than 2 x 10(-17) cm3 molecule(-1) s(-1), while the reactivity with OH was less than 6.8 x 10(-16) cm3 molecule(-1) s(-1), indicating low reactivity in the troposphere. Consequently, the lifetime of PFPMIE should be limited bytransport to the mesosphere, where photolysis by Lyman-alpha radiation at 121.6 nm will be efficient. By analogy to perfluorinated alkanes, the lower limit for the total atmospheric lifetime is 800 years. PFPMIE was shown to have instantaneous radiative forcing of 0.65 W m(-2) ppb(-1), which corresponds to a global warming potential on a 100 year time scale of 9000 relative to CO2 and 1.95 relative to CFC-11.

Atmosphere↗
PubMed2006

Persistent organic pollutants in the equatorial atmosphere over the open Indian Ocean.

Twelve air samples collected over the Indian Ocean by a high volume air sampler between August 2004 and August 2005 were analyzed for selected polychlorinated biphenyl (PCB) congeners and organochlorine pesticides. The region of the Indian Ocean and adjacent countries is likely to be acting as a source of selected POPs to the global environment. Data were compared with those reported for the last 30 years to examine historical trends of selected persistent organic pollutants (POPs) over the Indian Ocean. Compound concentrations were influenced by the proximity to land and air mass origins. Higher concentrations of atmospheric sigmaPCBs (50-114 pg m(-3)) were found on the remote islands of Chagos Archipelago and Gan, Maldives, and in the proximity of Jakarta, Indonesia, and Singapore. Military activities and unregulated waste combustion were identified as possible sources for atmospheric PCB contaminations at the more remote areas. The highest concentrations of organochlorine pesticides were found adjacent to the coastline of Sumatra and Singapore, where sigmaDDTs (dichlorodiphenyltrichloroethane) and sigmaHCHs (hexacyclohexanes) were as high as 30 and 100 pg m(-3), respectively. A comparison study for the last 30 years over six regions of the Indian Ocean showed that the concentrations of organochlorine pesticides have declined significantly, by a magnitude of two, since the mid 1970s, but were highest at the beginning of the 1990s. The time trend of PCB contamination in the atmosphere over the Indian Ocean is less apparent. The decline of atmospheric POPs over the Indian Ocean may be due to international regulation of the use of these compounds.

Air Pollutants↗
PubMed2006

Spatial and seasonal variations of Hexachlorocyclohexanes (HCHs) and hexachlorobenzene (HCB) in the Arctic atmosphere.

Weekly high-volume air samples were collected between 2000 and 2003 at six Arctic sites, i.e., Alert, Kinngait, and Little Fox Lake (LFL) in Canada, Point Barrow in Alaska, Valkarkai in Russia, and Zeppelin in Norway. Hexachlorocyclohexanes (HCHs) and hexachlorobenzene (HCB) were quantified in all samples. Comparison showed that alpha-HCH and HCB were homogeneously distributed in the circumpolar atmosphere and uniform throughout the seasons. However, significantly higher atmospheric concentrations of alpha-HCH and HCB and strongertemperature dependence of alpha-HCH and gamma-HCH were found at LFL in Yukon (YK), which is unique among the sites by virtue of its high altitude and low latitude, resulting in higher precipitation rates and summer temperatures. Strong temperature dependence of alpha- and gamma-HCH at this location suggests that secondary emissions, i.e., re-evaporation from surfaces, were more important at this site than others. It is hypothesized that a higher precipitation rate at LFL facilitated the transfer of alpha-HCH from the atmosphere to surface media when technical HCH was still in use worldwide. On the other hand, higher temperature at LFL enhanced reevaporation to the atmosphere after the global ban of technical HCH. In contrast to alpha-HCH and HCB, larger spatial and seasonal differences were seen for gamma-HCH (a currently used pesticide), which likely reflect the influence of different primary contaminant sources on different Arctic locations. Fugacity ratios suggest a net deposition potential of HCB from air to seawater, whereas seawater/air exchange direction of alpha-HCH varies in the circumpolar environment.

Air Pollutants↗
PubMed2001

A coupled ecosystem-climate model for predicting the methane concentration in the Archean atmosphere.

A simple coupled ecosystem-climate model is described that can predict levels of atmospheric CH4, CO2, and H2 during the Late Archean, given observed constraints on Earth's surface temperature. We find that methanogenic bacteria should have converted most of the available atmospheric H2 into CH4, and that CH4 may have been equal in importance to CO2 as a greenhouse gas. Photolysis of this CH4 may have produced a hydrocarbon smog layer that would have shielded the surface from solar UV radiation. Methanotrophic bacteria would have consumed some of the atmospheric CH4, but they would have been incapable of reducing CH4 to modern levels. The rise of O2 around 2.3 Ga would have drastically reduced the atmospheric CH4 concentration and may thereby have triggered the Huronian glaciation.

Aerobiosis↗
PubMed2002

Possible impact of a primordial oil slick on atmospheric and chemical evolution.

Low molecular weight liquid hydrocarbons from various sources, could have formed an oil layer covering the primeval ocean (present already 4.0-4.4 x 10(9) yr ago), preventing water from evaporating into the atmosphere. Water from other sources, precipitated by cold traps at higher altitude in the atmosphere, becomes trapped in the ocean. In a thereby more dry and presumably reducing atmosphere (before 3.9 x 10(9) yr ago) even more hydrocarbons, as well as reactive molecules will form. An oil layer can possibly act as a dry solvent for reactions, where the reactive molecules can produce monomers and condensing agents. Monomers and eventual polymers formed could become strongly concentrated at the oil-water interface, favouring molecular interactions at high mobility and low dilution, without exposure to the destructive action of UV-light. Increased water leakiness of the oil layer due to accumulation of polar molecules within, would lead to photooxidation of liquid hydrocarbons, and subsequent emulsification at the oil-water interface, forming cellular structures. The atmosphere would then have lost its reducing character.

Atmosphere↗
PubMed1989

Satellite observation of atmospheric nuclear gamma radiation.

We present a satellite observation of the spectrum of gamma radiation from the Earth's atmosphere in the energy interval from 300 keV to 8.5 MeV. The data were accumulated by the gamma ray spectrometer on the Solar Maximum Mission over 3 1/2 years, from 1980 to 1983. The excellent statistical accuracy of the data allows 20 atmospheric line features to be identified. The features are superimposed on a continuum background which is modeled using a power law with index -1.16. Many of these features contain a blend of more than one nuclear line. All of these lines (with the exception of the 511-keV annihilation line) are Doppler broadened. Line energies and intensities are consistent with production by secondary neutrons interacting with atmospheric 14N and 16O. Although we find no evidence for other production mechanisms, we cannot rule out significant contributions from direct excitation or spallation by primary cosmic ray protons. The relative intensities of the observed line features are in fair agreement with theoretical models; however, existing models are limited by the availability of neutron cross sections, especially at high energies. The intensity and spectrum of photons at energies below the 511-keV line, in excess of a power law continuum, can be explained by Compton scattering of the annihilation line photons in traversing an average of approximately 21 g cm-2 of atmosphere.

Astronomy↗
PubMed1987

Gas chromatographic instrumentation for the analysis of aerosols and gases in Titan's atmosphere.

During the next decade or so, NASA, in conjunction with the European Space Agency, plans to send a spacecraft to the Saturnian system so that local studies of Saturn and its satellite, Titan, can be made. In order to study the atmosphere of Titan, analysis of both aerosols and gases will have to be made. To accomplish this, gas chromatographic instrumentation for the collection and analysis of organic gases and aerosols in Titan's atmosphere is being developed. The aerosols will be collected and then subjected to pyrolysis-gas chromatography. Results using a simple pyrolysis-GC system and tholin, made by subjecting a nominal Titan mixture (96.8% N2, 3% CH4, 0.2% H2) to laser-supported shocks, show that many compounds, including hydrocarbons and simple nitriles, can be identified by this technique. Atmospheric gases will be collected using large volume (>10 cm3) sample loops and then analyzed by gas chromatography. Large volume samples are required because the ambient pressures, where the probe instruments are first deployed, will be low (<10 mbar). Preliminary studies using a 20 cm3 sampling system and a very sensitive meta-stable ionization detector show that hydrocarbon components at the 10 ppb level can be detected. Work will continue to improve GC sensitivity, minimize analysis time, and develop interfaces with suitable sample collectors for analysis of atmospheres by future spacecraft.

Aerosols↗
PubMed1989

Photochemistry of CO and H2O: analysis of laboratory experiments and applications to the prebiotic Earth's atmosphere.

The role photochemical reactions in the early Earth's atmosphere played in the prebiotic synthesis of simple organic molecules was examined. We have extended an earlier calculation of formaldehyde production rates to more reduced carbon species, such as methanol, methane, and acetaldehyde. We have simulated the experimental results of Bar-Nun and Chang (1983) as an acid in the construction of our photochemical scheme and as a way of validating our model. Our results indicate that some fraction of CO2 and H2 present in the primitive atmosphere could have been converted to simple organic molecules. The exact amount is dependent on the partial pressure of CO2 and H2 in the atmosphere and on what assumptions are made concerning the shape of the absorption spectra of CO2 and H2O. In particular, the results are most sensitive to the presence or absence of absorption at wavelengths longward of 2000 angstroms. We also find that small quantities of CH4 could have been present in the prebiotic Earth's atmosphere as the result of the photoreduction of CO.

Atmosphere↗
PubMed1986

Chemical effects of large impacts on the Earth's primitive atmosphere.

Intense bombardment of the moon and terrestrial planets approximately 3.9-4.0 x 10(9) years ago could have caused the chemical reprocessing of the Earth's primitive atmosphere. In particular, the shock heating and rapid quenching caused by the impact of large bodies into the atmosphere could produce molecules such as HCN and H2CO4 which are important precursors for the abiotic synthesis of complex organic molecules. Here we model the production of HCN and H2CO by thermochemical equilibrium and chemical kinetic calculations of the composition of shocked air parcels for a wide range of temperatures, pressures and initial compositions. For atmospheres with C/O > or = 1, our results suggest that bolide impacts cause HCN volume mixing ratios of approximately 10(-3) to 10(-5) in the impact region and global average ratios of 10(-5) to 10(-12). The corresponding H2CO mixing ratios in the impact region are 10(-7) to 10(-9); no-global mixing can occur, however, as H2CO is rapidly destroyed or rained out of the atmosphere within days to hours. Rainout to the oceans of 3-15% of the HCN produced can provide approximately (3-14) x 10(11) mol HCN per year. This is somewhat larger than other predicted sources of HCN and H2CO on the primitive Earth.

Atmosphere↗
PubMed2000

Atmospheric carbon dioxide concentrations over the past 60 million years.

Knowledge of the evolution of atmospheric carbon dioxide concentrations throughout the Earth's history is important for a reconstruction of the links between climate and radiative forcing of the Earth's surface temperatures. Although atmospheric carbon dioxide concentrations in the early Cenozoic era (about 60 Myr ago) are widely believed to have been higher than at present, there is disagreement regarding the exact carbon dioxide levels, the timing of the decline and the mechanisms that are most important for the control of CO2 concentrations over geological timescales. Here we use the boron-isotope ratios of ancient planktonic foraminifer shells to estimate the pH of surface-layer sea water throughout the past 60 million years, which can be used to reconstruct atmospheric CO2 concentrations. We estimate CO2 concentrations of more than 2,000 p.p.m. for the late Palaeocene and earliest Eocene periods (from about 60 to 52 Myr ago), and find an erratic decline between 55 and 40 Myr ago that may have been caused by reduced CO2 outgassing from ocean ridges, volcanoes and metamorphic belts and increased carbon burial. Since the early Miocene (about 24 Myr ago), atmospheric CO2 concentrations appear to have remained below 500 p.p.m. and were more stable than before, although transient intervals of CO2 reduction may have occurred during periods of rapid cooling approximately 15 and 3 Myr ago.

Animals↗
PubMed2005

Indication of drier periods on Mars from the chemistry and mineralogy of atmospheric dust.

The ubiquitous atmospheric dust on Mars is well mixed by periodic global dust storms, and such dust carries information about the environment in which it once formed and hence about the history of water on Mars. The Mars Exploration Rovers have permanent magnets to collect atmospheric dust for investigation by instruments on the rovers. Here we report results from Mössbauer spectroscopy and X-ray fluorescence of dust particles captured from the martian atmosphere by the magnets. The dust on the magnets contains magnetite and olivine; this indicates a basaltic origin of the dust and shows that magnetite, not maghemite, is the mineral mainly responsible for the magnetic properties of the dust. Furthermore, the dust on the magnets contains some ferric oxides, probably including nanocrystalline phases, so some alteration or oxidation of the basaltic dust seems to have occurred. The presence of olivine indicates that liquid water did not play a dominant role in the processes that formed the atmospheric dust.

Atmosphere↗
PubMed2001

Effect of oregano essential oil on microbiological and physico-chemical attributes of minced meat stored in air and modified atmospheres.

AIMS: This study aimed to determine the combined effect of packaging (air, modified atmosphere) with or without the addition of essential oil not only on the selection of microbial association of meat but also to determine any significant difference in microbial metabolites produced from the prevailing bacteria. METHODS AND RESULTS: Samples of minced meat were mixed with different concentration of oregano essential oil (0, 0.05, 0.5 and 1% v/w) and packed under aerobic or with modified atmosphere (Mixed Gas Modified Atmosphere--MGMA, 40% CO2/30% N2/30% O2; or CO2 Modified Atmosphere--COMA, 100% CO2) and stored at 5 degrees C. In all packaging conditions, only concentrations of 0.5% and 1% oregano oil were effective. Inhibition was evident in the order air < MGMA < COMA. Oregano essential oil delayed glucose and lactate consumption aerobically as well as under MGMA. pH changes were also evident. Furthermore, proteolysis was significantly inhibited in aerobically stored samples, and so was the production of acetate under MAP. Similar results were obtained for the other organic acids eluted from HPLC column. CONCLUSIONS: Oregano essential oil delayed microbial growth and suppressed the final counts of the spoilage micro-organisms. It also caused a pronounced alteration in the physico-chemical properties of the minced meat. SIGNIFICANCE AND IMPACT OF THE STUDY: Microbial analysis alone as spoilage index may misrepresent the effect of a hurdle such as essential oils on spoilage.

Aerobiosis↗
PubMed2002

High-oxygen and high-carbon dioxide containing atmospheres inhibit growth of food associated moulds.

AIMS: The objective of this study was to determine the relationship between the growth of three foodborne fungi and high-oxygen modified atmosphere. METHODS AND RESULTS: Petri dishes were incubated in a series of connected flasks, which were placed in a climatized room and flushed continuously with the desired gas atmosphere. A combination of 80% oxygen and 20% carbon dioxide resulted in reduced growth of Rhizopus stolonifer, Botrytis cinerea and Penicillium discolor compared with ambient atmosphere conditions. Combining 80% oxygen and 20% carbon dioxide at 10 degrees C arrested growth of B. cinerea for 17 d while an elevated carbon dioxide concentration only inhibited growth up to 11 d. In addition, the peroxidase activity was doubled at 80% oxygen and decreased when 10% carbon dioxide was present. IMPACT OF THE STUDY: This study demonstrates the potential use of elevated oxygen levels in a modified atmosphere to inhibit food-associated mould growth.

Atmosphere↗
PubMed2000

Atmospheric energy for subsurface life on Mars?

The location and density of biologically useful energy sources on Mars will limit the biomass, spatial distribution, and organism size of any biota. Subsurface Martian organisms could be supplied with a large energy flux from the oxidation of photochemically produced atmospheric H(2) and CO diffusing into the regolith. However, surface abundance measurements of these gases demonstrate that no more than a few percent of this available flux is actually being consumed, suggesting that biological activity driven by atmospheric H(2) and CO is limited in the top few hundred meters of the subsurface. This is significant because the available but unused energy is extremely large: for organisms at 30-m depth, it is 2,000 times previous estimates of hydrothermal and chemical weathering energy and far exceeds the energy derivable from other atmospheric gases. This also implies that the apparent scarcity of life on Mars is not attributable to lack of energy. Instead, the availability of liquid water may be a more important factor limiting biological activity because the photochemical energy flux can only penetrate to 100- to 1,000-m depth, where most H(2)O is probably frozen. Because both atmospheric and Viking lander soil data provide little evidence for biological activity, the detection of short-lived trace gases will probably be a better indicator of any extant Martian life.

Atmosphere↗
PubMed2006

Atmospheric nitrogen deposition promotes carbon loss from peat bogs.

Peat bogs have historically represented exceptional carbon (C) sinks because of their extremely low decomposition rates and consequent accumulation of plant remnants as peat. Among the factors favoring that peat accumulation, a major role is played by the chemical quality of plant litter itself, which is poor in nutrients and characterized by polyphenols with a strong inhibitory effect on microbial breakdown. Because bogs receive their nutrient supply solely from atmospheric deposition, the global increase of atmospheric nitrogen (N) inputs as a consequence of human activities could potentially alter the litter chemistry with important, but still unknown, effects on their C balance. Here we present data showing the decomposition rates of recently formed litter peat samples collected in nine European countries under a natural gradient of atmospheric N deposition from approximately 0.2 to 2 g.m(-2).yr(-1). We found that enhanced decomposition rates for material accumulated under higher atmospheric N supplies resulted in higher carbon dioxide (CO2) emissions and dissolved organic carbon release. The increased N availability favored microbial decomposition (i) by removing N constraints on microbial metabolism and (ii) through a chemical amelioration of litter peat quality with a positive feedback on microbial enzymatic activity. Although some uncertainty remains about whether decay-resistant Sphagnum will continue to dominate litter peat, our data indicate that, even without such changes, increased N deposition poses a serious risk to our valuable peatland C sinks.

Atmosphere↗
PubMed2003

Fate and potential environmental effects of methylenediphenyl diisocyanate and toluene diisocyanate released into the atmosphere.

Information from a variety of sources has been collected and summarized to facilitate an overview of the atmospheric fate and potential environmental effects of emissions of methylenediphenyl diisocyanate (MDI) or toluene diisocyanate (TDI) to the atmosphere. Atmospheric emissions of both MDI and TDI are low, both in terms of concentration and mass, because of their low volatility and the need for careful control over all aspects of their lifecycle from manufacture through disposal. Typical emission losses for TDI are 25 g/t of TDI used in slabstock foam production. MDI emission losses are lower, often less than 1 g/t of MDI used. Dispersion modeling predicts that concentrations at the fenceline or beyond are very low for typical releases. Laboratory studies show that TDI (and by analogy MDI) does not react with water in the gas phase at a significant rate. The primary degradation reaction of these aromatic diisocyanates in the atmosphere is expected to be oxidation by OH radicals with an estimated half-life of one day. Laboratory studies also show that this reaction is not expected to result in increased ground-level ozone accumulation.

Aerosols↗
PubMed2005

Modeling mercury fluxes and concentrations in a Georgia watershed receiving atmospheric deposition load from direct and indirect sources.

This paper presents a modeling analysis of airborne mercury (Hg) deposited on the Ochlockonee River watershed located in Georgia. Atmospheric deposition monitoring and source attribution data were used along with simulation models to calculate Hg buildup in the subwatershed soils, its subsequent runoff loading and delivery through the tributaries, and its ultimate fate in the mainstem river. The terrestrial model calculated annual watershed yields for total Hg ranging from 0.7 to 1.1 microg/m2. Results suggest that approximately two-thirds of the atmospherically deposited Hg to the watershed is returned to the atmosphere, 10% is delivered to the river, and the rest is retained in the watershed. A check of the aquatic model results against survey data showed a reasonable agreement. Comparing observed and simulated total and methylmercury concentrations gave root mean square error values of 0.26 and 0.10 ng/L, respectively, in the water column, and 5.9 and 1 ng/g, respectively, in the upper sediment layer. Sensitivity analysis results imply that mercury in the Ochlockonee River is dominated by watershed runoff inputs and not by direct atmospheric deposition, and that methylmercury concentrations in the river are determined mainly by net methylation rates in the watershed, presumably in wetted soils and in the wetlands feeding the river.

Air Pollutants↗