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At least 631 records · Page 35Linked to original sources
PubMed1994

A photochemical model of the martian atmosphere.

The factors governing the amounts of CO, O2, and O3 in the martian atmosphere are investigated using a minimally constrained, one-dimensional photochemical model. We find that the incorporation of temperature-dependent CO2 absorption cross sections leads to an enhancement in the water photolysis rate, increasing the abundance of OH radicals to the point where the model CO abundance is smaller than observed. Good agreement between models and observations of CO, O2, O3, and the escape flux of atomic hydrogen can be achieved, using only gas-phase chemistry, by varying the recommended rate constants for the reactions CO + OH and OH + HO2 within their specified uncertainties. Similar revisions have been suggested to resolve discrepancies between models and observations of the terrestrial mesosphere. The oxygen escape flux plays a key role in the oxygen budget on Mars; as inferred from the observed atomic hydrogen escape, it is much larger than recent calculations of the exospheric escape rate for oxygen. Weathering of the surface may account for the imbalance. Quantification of the escape rates of oxygen and hydrogen from Mars is a worthwhile objective for an upcoming martian upper atmospheric mission. We also consider the possibility that HOx radicals may be catalytically destroyed on dust grains suspended in the atmosphere. Good agreement with the observed CO mixing ratio can be achieved via this mechanism, but the resulting ozone column is much higher than the observed quantity. We feel that there is no need at this time to invoke heterogeneous processes to reconcile models and observations.

Atmosphere↗
PubMed2000

Simulated navigation based on observed gradients of atmospheric trace gases (Models on pigeon homing, part 3).

An earlier developed model, simulating pigeon homing based on fictitious gradients of atmospheric odours, was applied to actually observed spatial distributions of volatile hydrocarbons. The model calculations demonstrate that sufficient information on a bird's current position with respect to home can be derived from the ratios among three or more chemical compounds which gradually vary over distances of several hundreds of kilometres, differently in different directions. Flight directions computed by model birds from such observed ratios are roughly but not perfectly homeward-oriented from most positions within the investigated radius of 200 km around home. Performances of model birds are at least as good as those of real pigeons in the field. According to calculations using atmospheric data collected under different wind directions, the birds might, but possibly need not, take the current weather conditions into account when evaluating olfactory signals. It is necessary, however, that the birds acquire, during their long-term stay at the home site, some knowledge of the directions of relevant gradients. Homing experiments with pigeons as well as measurements of atmospheric trace substances are consistent with the hypothesis that this knowledge is gained by correlating wind directions with specific changes of ratios among a number of compounds. This assumed process requires further elucidation.

Animals↗
PubMed1996

Video observations, atmospheric path, orbit and fragmentation record of the fall of the Peekskill meteorite.

Large Near-Earth-Asteroids have played a role in modifying the character of the surface geology of the Earth over long time scales through impacts. Recent modeling of the disruption of large meteoroids during atmospheric flight has emphasized the dramatic effects that smaller objects may also have on the Earth's surface. However, comparison of these models with observations has not been possible until now. Peekskill is only the fourth meteorite to have been recovered for which detailed and precise data exist on the meteoroid atmospheric trajectory and orbit. Consequently, there are few constraints on the position of meteorites in the solar system before impact on Earth. In this paper, the preliminary analysis based on 4 from all 15 video recordings of the fireball of October 9, 1992 which resulted in the fall of a 12.4 kg ordinary chondrite (H6 monomict breccia) in Peekskill, New York, will be given. Preliminary computations revealed that the Peekskill fireball was an Earth-grazing event, the third such case with precise data available. The body with an initial mass of the order of 10(4) kg was in a pre-collision orbit with a = 1.5 AU, an aphelion of slightly over 2 AU and an inclination of 5 degrees. The no-atmosphere geocentric trajectory would have lead to a perigee of 22 km above the Earth's surface, but the body never reached this point due to tremendous fragmentation and other forms of ablation. The dark flight of the recovered meteorite started from a height of 30 km, when the velocity dropped below 3 km/s, and the body continued 50 km more without ablation, until it hit a parked car in Peekskill, New York with a velocity of about 80 m/s. Our observations are the first video records of a bright fireball and the first motion pictures of a fireball with an associated meteorite fall.

Astronomical Phenomena↗
PubMed1981

Rates of fixation by lightning of carbon and nitrogen in possible primitive atmospheres.

A thermochemical-hydrodynamic model of the production of trace species by electrical discharges has been used to estimate the rates of fixation of C and N by lightning in the primitive atmosphere. Calculations for various possible mixtures of CH4, CO2, CO, N2, H2, and H2O reveal that the prime species produced were probably HCN and NO and that the key parameter determining the rates of fixation was the ratio of C atoms to O atoms in the atmosphere. Atmospheres with C more abundant than O have large HCN fixation rates, in excess of 10(17) molecules J-1, but small NO yields. However, when O is more abundant than C, the NO fixation rate approaches 10(17) molecules J-1 while the HCN yield is small. The implications for the evolution of life are discussed.

Atmosphere↗
PubMed1984

The evolution of the prebiotic atmosphere.

One-dimensional radiative convective and photochemical models are used to estimate the vertical temperature structure and composition of the earth's prebiotic atmosphere. Greatly enhanced CO2 levels (100-1000 times present) are required to keep the mean surface temperature above freezing in the face of decreased solar luminosity during the earth's early history. Such high CO2 partial pressures would have affected the atmospheric oxidation state by facilitating the photochemical production of soluble species including H2O2 and H2CO. Oxidation of ferrous iron in the oceans by H2O2 dissolved in rainwater should have kept the atmospheric H2 mixing ratio above 2x10(-4) and the ground-level O2 mixing ratio below 10(-11), regardless of the magnitude of the rate of volcanic release of reduced gases.

Atmosphere↗
PubMed1983

Prebiotic synthesis in atmospheres containing CH4, CO, and CO2. I. Amino acids.

The prebiotic synthesis of organic compounds using a spark discharge on various simulated primitive earth atmospheres at 25 degrees C has been studied. Methane mixtures contained H2 + CH4 + H2O + N2 + NH3 with H2/CH4 molar ratios from 0 to 4 and pNH3 = 0.1 torr. A similar set of experiments without added NH3 was performed. The yields of amino acids (1.2 to 4.7% based on the carbon) are approximately independent of the H2/CH4 ratio and whether NH3 was present, and a wide variety of amino acids are obtained. Mixtures of H2 + CO + H2O + N2 and H2 + CO2 + H2O + N2, with and without added NH3, all gave about 2% yields of amino acids at H2/CO and H2/CO2 ratios of 2 to 4. For a H2/CO2 ratio of 0, the yield of amino acids is extremely low (10(-3)%). Glycine is almost the only amino acid produced from CO and CO2 model atmospheres. These results show that the maximum yield is about the same for the three carbon sources at high H2/carbon ratios, but that CH4 is superior at low H2/carbon ratios. In addition, CH4 gives a much greater variety of amino acids than either CO or CO2. If it is assumed that an abundance of amino acids more complex than glycine was required for the origin of life, then these results indicate the requirement for CH4 in the primitive atmosphere.

Amino Acids↗
PubMed1983

Prebiotic synthesis in atmospheres containing CH4, CO, and CO2. II. Hydrogen cyanide, formaldehyde and ammonia.

The electric discharge synthesis of HCN, H2CO, NH3 and urea has been investigated using various mixtures of CH4, CO, CO2, N2, NH3, H2O, and H2. HCN and H2CO were each synthesized in yields as high as 10% from CH4 as a carbon source. Similar yields were obtained from CO when H2/CO greater than 1.0 and from CO2 when H2/CO2 greater than 2.0. At H2/CO2 less than 1.0 the yields fall off drastically. Good yields of NH3 (0.7 to 5%) and fair yields of urea (0.02 to 0.63%) based on nitrogen were also obtained. The directly synthesized NH3 together with the NH3 obtained from the hydrolysis of HCN, nitriles and urea could have been a major source of ammonia in the atmosphere and oceans of the primitive earth. These results show that prebiotic syntheses from HCN and H2CO to give products such as purines and sugars and some amino acids could have occurred in primitive atmospheres containing CO and CO2 provided the H2/CO and H2/CO2 ratios were greater than about 1.0. Methane containing atmospheres give comparable quantities of HCN and H2CO, and are superior in the synthesis of amino acids.

Ammonia↗
PubMed2002

Effect of atmospheric factors on the incidence of Bell's palsy.

To assess the possible influence of atmospheric factors on the incidence of Bell's palsy, a retrospective case review of patients seen between 1 January 1992 and 30 June 1996, was designed. The population included all Bell's palsy patients in whom the exact date of onset of paralysis (day, month, year) was known. The following parameters were registered daily by the Spanish National Service of Meteorology throughout the period of survey: temperature, atmospheric pressure and air pollutants (total number of particles and levels of SO2, CO, O3, NO2, NO, CH4 and total organic carbon). The only factor significantly related to Bell's palsy was temperature (P = 0.0164). Lower temperatures were associated with a higher incidence of Bell's palsy. A relationship between atmospheric pressure and/or air pollutants and Bell's palsy was not found.

Adolescent↗
PubMed2000

Microwave assisted extraction of polycyclic aromatic hydrocarbons from atmospheric particulate samples.

For several years, microwave assisted extraction (MAE) was applied to extract organic compounds such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls, etc., from soils, sediments and standard reference materials. Very few authors applied this methodology for the extraction of PAHs from atmospheric particulate matter. In the present study, MAE of polycyclic aromatic hydrocarbons with hexane/acetone (1:1) from real atmospheric particulate samples was investigated and the effect of microwave energy and irradiation time studied. The yields of extracted compounds obtained by microwave irradiation were compared with those obtained using traditional Soxhlet extraction. MAE was evaluated using spiked real atmospheric particulate samples and two standard reference materials. Analytical determinations of PAHs were carried out by high performance liquid chromatography (HPLC) with ultraviolet and fluorescence detection. The best recoveries were achieved with a microwave energy of 400 W and an irradiation time of 20 min.

Air Pollutants↗
PubMed2002

Chemolithoautotrophic nitrifiers in the phyllosphere of a spruce ecosystem receiving high atmospheric nitrogen input.

Evidence is presented for the first time that chemolithoautotrophic ammonia oxidizers (CAO) and chemolithoautotrophic nitrite oxidizers (CNO) colonize in appreciable cell numbers the phyllosphere of spruce trees in a forest ecosystem exposed for decades to high levels of atmospheric nitrogen (The Höglwald Forest, Bavaria, Germany). The results strongly indicate that both, CAO and CNO are predominantly located inside the spruce needles, most likely within the stomatal cavity. These results are further supported by field experiments of NH3 uptake into twigs on intact spruce trees in the presence and absence of 10 Pa acetylene, an inhibitor of the ammonia monooxygenase of CAO. It is clearly demonstrated for the first time that in situ uptake of NH3 from the atmosphere into spruce needles exposed to high levels of atmospheric N is not catalyzed exclusively by the tree, but is the result of combined activities of both, the spruce trees and the chemolithoautotrophic nitrifiers colonizing the needles.

Animals↗
PubMed2001

A short-term exposure of cucumber plants to rising atmospheric CO2 increases leaf carbohydrate content and enhances nitrate reductase expression and activity.

Nitrate reductase (NR; EC 1.6.6.1) is the first enzyme of the nitrate-assimilatory pathway and is regulated transcriptionally and post-translationally by several metabolic and environmental signals. To investigate whether NR is controlled by the rate of photosynthetic CO2 assimilation in cucumber (Cucumis sastivus L.), intact plants were exposed, after the dark period, to light under different atmospheric CO2 concentrations (100, 400 and 2,000 microL x L(-1)) for 2 h. The in-vivo rates of net CO2 assimilation correlated with atmospheric CO2 concentrations. The CO2-fixation rate under 2,000 microL x L(-1) CO2 was 2.4- and 5.4-fold higher than under 400 and 100 microL x L(-1), respectively. Stomatal conductances and transpiration rates were almost identical after the 2-h light period under the various CO2 concentrations tested. Increasing atmospheric CO2 concentrations caused concomitant increases in the contents of starch and soluble sugars in the leaves and a decrease in the nitrate content. The activity and activation state of NR were both higher under elevated CO2 than under low CO2. High CO2 also enhanced NR-gene expression in the leaves. Sugars were supplied via roots to intact carbohydrate-starved plants and NR mRNA levels were analysed after 7 h. Fructose markedly stimulated NR-gene transcription in both leaves and roots. It is concluded that, in cucumber plants, the rate of CO2 assimilation controls the rate of nitrate assimilation by modulation of NR expression and activity, and that sugars are presumably involved as regulatory metabolites.

Atmosphere↗
PubMed2004

Correlations of life-span variation parameters in 128 successive generations of Drosophila melanogaster with changes in atmospheric pressure and geomagnetic activity.

Correlations between the parameters of life-span (LS) distribution of Drosophila melanogaster, including mean LS (MLS) and the time of 10 and 90% population mortality, and some geophysical parameters that are usually beyond the control of researchers dealing with laboratory cultures, including atmospheric pressure, solar activity indices (Wolf's sunspot numbers and 2,800-MHz radio flux), and geomagnetic activity (planetary index, K(p)), were studied. Geophysical data were obtained from free-access official web sites of the National Oceanic & Atmospheric Administration of the US Department of Commerce and the Institute of Terrestrial Magnetism and Radiowave Propagation of the Russian Academy of Sciences. The geophysical parameters were calculated only for the period corresponding to 10 days of preimaginal development of the flies from egg to imago. Canonical correlation analysis, calculation of the non-parametric Spearman rank-order correlation coefficients, and graphical data analysis were used. Highly significant correlations between parameters of LS distribution in males and females and environmental factors, such as the atmospheric pressure on the 4th and 5th day of development and geomagnetic activity indices (K(p)) on the 6th and 10th day of development were found, with correlation coefficients varying from 0.31 to 0.37 (P<0.02). Assuming a causal relationship between geophysical factors and LS, it may be hypothesized that energetically weak environmental factors determine the formation of LS oscillatory dynamics in laboratory populations. The possible mechanisms underlying the contribution of these environmental factors to the LS variation in successive generations are discussed.

Animals↗
PubMed2005

Survival of deep-sea shrimp (Alvinocaris sp.) during decompression and larval hatching at atmospheric pressure.

We report successful larval hatching of deep-sea shrimp after decompression to atmospheric pressure. Three specimens of deep-sea shrimp were collected from an ocean depth of 1157 m at cold-seep sites off Hatsushima Island in Sagami Bay, Japan, using a pressure-stat aquarium system. Phylogenetic analysis of Alvinocaris sp. based on cytochrome c oxidase subunit gene sequences confirmed that these species were a member of the genus Alvinocaris. All 3 specimens survived to reach atmospheric pressure conditions after stepwise 63-day decompression. Two of the specimens contained eggs, which hatched after 10 and 16 days, respectively, of full decompression. Although no molting of the shrimp larvae was observed during 74 days of rearing under atmospheric pressure, the larvae developed conventional dark-adapted eyes after 15 days.

Animals↗
PubMed2005

Biomonitoring of lead in atmospheric environment of an urban center of the Ganga Plain, India.

Monitoring of atmospheric lead from the Dalbergia sissoo tree was undertaken at Lucknow urban centre of the Ganga Plain, India. A total of 26 leaf samples were collected in spring, monsoon and winter seasons from 16 sampling sites and was analysed by Atomic Absorption Spectrophotometry method. Lead concentrations were low in spring season, increased in monsoon to winter seasons and range from 2.1 to 28.2 microg/g (dry wt.). This accumulative response of lead in the tree leaves is directly linked with the exposure time of automobile emission that is considered to be the predominant source for it. Highway localities show higher lead concentrations by a factor of 2 as compared to urban localities. Highest concentration was recorded at Sitapur Road (National Highway No. 24) in winter season. A linear quantitative relationship between urban air-lead levels and lead-in-the Dalbergia sissoo leaves is used to infer the qualitative assessment of present day atmospheric lead pollution. Reported results suggest a drastic reduction in mean lead concentration in Lucknow urban air from 1.32 microg/m3 in 1994 to 0.19 microg/m3 in 2002. Similarly, mean lead concentration in the tree leaves during winter season also dropped from 17.9 microg/g in 1994 to 8.1 microg/g in 2004. Despite of increasing urban population, urban area, vehicle population and traffic density, the introduction of unleaded-petrol (vehicular fuel) keeps lead level in the urban environment of Lucknow much lower than the past. Like Lucknow, other urban centres of the Ganga Plain are also on way to the exponential increase in pressure of urbanization. An appropriate urban public transport planning is required to provide healthy atmospheric environment for millions of people especially future young generation.

Air Pollutants↗
PubMed2006

Retrieval and monitoring of atmospheric trace gas concentrations in nadir and limb geometry using the space-borne SCIAMACHY instrument.

The Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) onboard the European Envisat spacecraft performs continuous spectral observations of reflected, scattered and transmitted sunlight in various observation geometries. A unique feature of SCIAMACHY is the capability of probing the atmosphere in three different observation geometries:The nadir, limb, and occultation measurement modes. In nadir mode, column densities of trace gases are retrieved with a spatial resolution of typically 30 x 60 km using the Differential Optical Absorption Spectroscopy (DOAS) technique (Platt and Perner, 1983). Alternating with the nadir measurement, vertical profiles of absorber concentration in the stratosphere are derived in limb and occultation. In this paper we present an overview over some applications of SCIAMACHY data in space-based monitoring of atmospheric pollution. The DOAS algorithms for the retrieval of total column amounts from nadir spectra are briefly described and case studies of pollution events are presented. We also illustrate the technique used to derive stratospheric concentration profiles from limb observations and show comparisons with other remote sensing systems. Special emphasis will be given to techniques, which take advantage of SCIAMACHY's different viewing geometries. In particular, we will discuss the potential and limits of strategies to infer tropospheric abundances of O3 and NO2.

Air Pollutants↗
PubMed1987

Atmospheric H2O2 measurement: comparison of cold trap method with impinger bubbling method.

Collection of atmospheric H2O2 was performed by a cold trap method using dry ice-acetone as the refrigerant. The air was drawn by a pump into a glass gas trap immersed in the dry ice-acetone slush in a dewar flask at a flow rate of 2.5 l min-1 for approximately 2 h. Collection efficiency was > 99% and negligible interferences by O3, SO2 or organic matter with the collected H2O2 in the trap were observed. This method was compared with the air impinger bubbling method which has been previously described (Kok et al., 1978a, b, Envir. Sci. Technol. 12, 1072-1080). The measured total peroxide (H2O2 + organic peroxide) values in a series of aim samples collected by the impinger bubbling method (0.06-3.7 ppb) were always higher than those obtained by the cold trap method (0.02-1.2 ppb). Laboratory experiments suggest that the difference in values between the two methods probably results from the aqueous phase generation of H2O2 and organic peroxide in the impinger solution by a reaction of atmospheric O3 with olefinic and aromatic compounds. If these O3-organic compound reactions which occur in the impinger also occur in aqueous droplets in the atmosphere, the process could be very important for aqueous phase generation of H2O2 in clouds and rainwater.

Acetone↗
PubMed1985

Effect of atmospheric ions on hippocampal pyramidal neuron responsiveness to serotonin.

The effect of long-term exposure to positive or negative atmospheric ions on the responsiveness of rat forebrain neurons to serotonin (5-HT) was studied. Male Sprague-Dawley rats were exposed to positive or negative ions (1.5 X 10(6) ions/ml) for 21 days, and a third group of rats served as controls. Unitary extracellular recordings from pyramidal neurons of the CA1 and CA3 regions of the dorsal hippocampus were obtained under urethane anesthesia, and their responsiveness to microiontophoretically applied acetylcholine (ACh), norepinephrine (NE) and 5-HT was assessed. Spontaneous rate of discharge and sensitivity to NE and ACh of hippocampal neurons were not affected by exposure to atmospheric ions. Exposure to negative ions increased and that to positive ions decreased the responsiveness of these neurons to 5-HT. During the winter, a circadian rhythm of responsiveness to 5-HT was observed in the control group, sensitivity being lowest in the morning and highest in the evening. Exposure to ions disrupted this circadian rhythm; in rats exposed to negative ions, responsiveness throughout the day was similar to that observed in the evening in the controls, whereas in rats exposed to positive ions, the circadian rhythm of responsiveness to 5-HT was inverted. Brain concentrations of 5-HT, tryptophan, and 5-hydroxyindoleacetic acid were unchanged by exposure to atmospheric ions.

Acetylcholine↗
PubMed1988

HDO in the Martian atmosphere: implications for the abundance of crustal water.

The physical and chemical processes that lead to the preferential escape of hydrogen over deuterium in the Martian atmosphere are studied in detail using a one-dimensional photochemical model. Comparison of our theory with recent observations of HDO suggests that, averaged over the planet, Mars contains 0.2 m of crustal water that is exchangeable with the atmosphere. Our estimate is considerably lower than recent estimates of subsurface water on Mars based on geomorphological analysis of Viking images. The estimate can be reconciled if only a small fraction of crustal water can exchange with the atmosphere.

Atmosphere↗