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At least 667 records · Page 37Linked to original sources
PubMed2005

Atmospheric polycyclic aromatic hydrocarbons: size distribution, estimation of their risk and their depositions to the human respiratory tract.

Polycyclic aromatic hydrocarbons (PAHs) in the atmosphere may be one of the causes of lung cancer. However, in many countries including Japan, only benzo[a]pyrene is regulated, though more toxic PAHs than benzo[a]pyrene have been reported. Therefore, it is necessary to characterize the risk of atmospheric PAHs and to find major contributing compounds that can act as suitable indicators for estimating and monitoring the risk of PAHs as a whole. The primary objectives of this study are to investigate the risk of 22 combined atmospheric PAHs and to find major contributing compounds that can act as adequate indicators for estimating the risk. The average lifetime cancer risk for all 22 PAHs in winter was 1.7 x 10(-4) in the Yokohama residential area. Although benzo[a]pyrene has been considered to be a useful indicator in many countries, the present study also showed that benzo[a]pyrene contributed only ca. 40% of the total cancer risk for all 22 PAHs, as calculated by unit risk. Six PAHs (dibenzo[a,h]anthracene, benzo[b]fluoranthene, indeno[1,2,3-cd]perylene, dibenzo[a,h]pyrene, dibenzo[a,e]pyrene, and benzo[a]pyrene) contributed 93% of the overall risk. Therefore, these six PAHs, including the high molecular ones, would be better indicators of the risk than benzo[a]pyrene alone. The secondary objective of this study is to reveal the PAHs that are major contributors to the deposition that contribute to the total deposition of PAHs in the human respiratory tract. The results revealed that the same six PAHs identified using unit risk evaluation were large contributors in all five parts of the respiratory tracts in adult males in spite of deposition process. It was concluded that the reason for this was that these six PAHs had the same size distributions, of which the 0.43-1.1 microm fraction was the most largest, about 57-70% of the whole concentration.

Adult↗
PubMed2005

On the variations in the electrical state under specific meteorological conditions in the ground atmospheric layer in semi-arid areas.

The object of this study is to evaluate the role of synoptic situations or the combination of several environmental parameters typical for regions close to big deserts, as possible exterior pathogenic factors, which give rise to a number of sometimes medically unexplained symptoms and disorders of human well-being. We suppose that one of the most important causes might be atmospheric electricity, whose role in human life, health and feelings can scarcely be exaggerated; in particular, our research is concentrated on the influence of electromagnetic fields on some subsystems of the human organism. Discussed below are the results of one of the initial stages of our research into the problem of the variations in the electrical state in connection with meteorological conditions in the surface atmospheric layer. The environmental electrical state is determined by either global electrical effects or local factors, as the content of the air column and the meteorological conditions in this volume are tightly connected with air streams. Especially in our region, located between the Mediterranean Sea and the huge African and Asian deserts, the direction, duration and speed of the winds must play the dominant role, due to their control over the content and concentration of air-suspended particles N(T). Desert winds bring increased N(T) of enlarged solid grains, mostly charged, hotter temperature T(0), dryness and other perturbations in the usual weather state and, finally, in the atmospheric electric field intensity E. Within limited intervals of wind speed V(w) (2-5 m x s(-1)) and concentration of enlarged solid grains N(T) (500-4500 grains cm(-3)), the correlation coefficients between E and N(T) and V(w) can reach more than 0.90. Outside these ranges, considerably increased N(T) or several combinations of wind direction with V(w) (not necessarily strong winds) lead to the principal change in the values of E and the form of its diurnal distribution from what is usual for stable weather. For moderately polluted air, the dependence of E on N(T) can be approximated well enough by a polynomial of the second degree; in a dust storm, this function is very close to the log-normal distribution.

Air Pollution↗
PubMed2005

Contribution of trace metals from atmospheric deposition to stormwater runoff in a small impervious urban catchment.

The contribution of atmospheric deposition to emissions of trace metals in stormwater runoff was investigated by quantifying wet and dry deposition fluxes and stormwater discharges within a small, highly impervious urban catchment in Los Angeles. At the beginning of the dry season in spring 2003, dry deposition measurements of chromium, copper, lead, nickel, and zinc were made monthly for 1 year. Stormwater runoff and wet deposition samples also were collected, and loading estimates of total annual deposition (wet+dry) were compared with annual stormwater loads. Wet deposition contributed 1-10% of the total deposition inside the catchment, indicating the dominance of dry deposition in semi-arid regions such as Los Angeles. Based on the ratio of total deposition to stormwater, atmospheric deposition potentially accounted for as much as 57-100% of the total trace metal loads in stormwater within the study area. Despite potential bias attributable to processes that were not quantified in this study (e.g., resuspension out of the catchment or sequestration within the catchment), these results demonstrate atmospheric deposition represents an important source of trace metals in stormwater to waterbodies near urban centers.

Air Pollutants↗
PubMed1998

Evolution of the atmosphere.

Planetary atmospheres depend fundamentally upon their geochemical inventory, temperature and the ability of their gravitational field to retain gases. In the case of Earth and other inner planets, early outgassing released mainly carbon dioxide and water vapour. The secondary veneer of comets and meteorites added further volatiles. Photodissociation caused secondary changes, including the production of traces of oxygen from water. Earth's gravity cannot retain light gases, including hydrogen. but retains oxygen. Water vapour generally does not pass the cold trap at the stratopause. In the archaean, early evolution of life, probably in hydrothermal vents, and the subsequent development of photosynthesis in surface waters, produced oxygen, at 3500 Ma or even earlier, becoming a significant component of the atmosphere from about 2000 Ma. Thereafter banded iron formations became rare, and iron was deposited in oxidized red beds. Atmospheric levels of carbon dioxide and oxygen have varied during the Phanerozoic: major changes may have caused extinctions. particularly the Permian/Triassic. The declining greenhouse effect due to the long-term decrease in carbon dioxide has largely offset increasing solar luminosity, and changes in carbon dioxide levels relate strongly to cycles of glaciation.

Atmosphere↗
PubMed2002

C2-C8 hydrocarbon measurement and quality control procedures at the Global Atmosphere Watch Observatory Hohenpeissenberg.

A new automated on-line GC-flame ionization detection system for long-term stationary measurements of atmospheric C2-C8 hydrocarbons in the lower ppt range is described. The system is operated at the Global Atmosphere Watch Observatory Hohenpeissenberg (47 degrees 48'N, 11 degrees 01'E) in rural south Germany. Atmospheric mixing ratios of more than 40 different hydrocarbons can be continuously measured in 80 min time intervals. Corresponding detection limits are below 3 ppt, except for propene, butenes and benzene (about 10 ppt). Detailed quality assurance and quality control protocols are described which are applied to routine operation and data analysis. The various error contributions, overall precision, and accuracy for all measured compounds are discussed in detail. Typical ambient air mixing ratios are in the range of a few ppt to a few ppb, and corresponding measurement accuracies are below 10% or 10 ppt. For less than 20% of the analyzed compounds measurement accuracies are worse, mainly because of insufficient peak separation, blank values or reduced reproducibilities. The present system was tested in international intercomparison experiments (NOMHICE, AMOHA). For most of the C2-C8 hydrocarbons analyzed, our results agreed better than +/- 10% (20% NOMHICE phase 5) or +/- 10 ppt with the corresponding reference values.

Atmosphere↗
PubMed2003

Stability studies of propoxur herbicide in environmental water samples by liquid chromatography-atmospheric pressure chemical ionization ion-trap mass spectrometry.

Liquid chromatography-atmospheric pressure ionization ion-trap mass spectrometry has been investigated for the analysis of polar pesticides in water. The degradation behavior of propoxur, selected as a model pesticide belonging to the N-methylcarbamate group, in various aqueous matrices (Milli-Q water, drinking water, rain water, seawater and river water) was investigated. Two interfaces of atmospheric pressure ionization, atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI), were compared during the study. Propoxur and its transformation product (N-methylformamide) were best ionized as positive ions with both APCI and ESI, while another transformation product (2-isopropoxyphenol) yielded stronger signals as negative ions only with APCI. In addition, the effects of various pH, matrix type and irradiation sources (sunlight, darkness, indoor lighting and artificial UV lamp) on the chemical degradation (hydrolysis) were also assessed. From the kinetic studies of degradation, it was found that the half-life of propoxur was reduced from 327 to 161 h in Milli-Q water with variation of irradiation conditions from dark to sunlight exposure. Degradation rates largely increased with increasing pH. The half-life of the target compound dissolved in Milli-Q water under darkness decreased from 407 to 3 h when the pH of Milli-Q water was increased from 5 to 8.5. These suggest that hydrolysis of propoxur is light-intensity and pH-dependent. In order to mimic contaminated natural environmental waters, propoxur was spiked into real water samples at 30 microg/l. The degradation of propoxur in such water samples under various conditions were studied in detail and compared. With the ion trap run in a time-scheduled single ion monitoring mode, typical limits of detection of the instrument were in the range of 1-10 microg/l.

Atmospheric Pressure↗
PubMed2001

Detecting organic tracers from biomass burning in the atmosphere.

This is a brief review key to the literature on the determination of organic tracers from biomass burning which are detectable even after long-range global transport in total extracts of atmospheric particles. The major tracers are thermal degradation products from the biopolymer cellulose, namely the didehydromonosaccharide derivatives levoglucosan, galactosan and mannosan and the resin acid derivative dehydroabietic acid, with minor beta-sitosterol. Dehydroabietic acid is emitted primarily from burning of conifer fuel and these tracers are found in most aerosol samples from the North American continent. Particulate matter from the atmosphere over oceanic areas contains organic tracers from both natural and biomass burning emissions. The major biomarker compounds characterized are natural products from continental vegetation consisting primarily of epicuticular wax components and trace components from biomass burning emissions. The presence of these tracers in atmospheric particulate matter over the ocean confirms the long-range transport of smoke from biomass burning off the continents.

Abietanes↗
PubMedDate not supplied

On the origin of Titan's atmosphere.

The present atmosphere of Titan exhibits evidence of extensive evolution, in the form of rapid photochemical destruction of methane and a large fractionation of the nitrogen and oxygen isotopes. Attempts to recover the initial inventory of volatiles lead toward a model in which nitrogen was originally supplied as NH3, essentially unmodified from its relative abundance in the outer solar nebula. Titan's atmospheric methane, in contrast, appears to have been formed from carbon and other carbon compounds, either by gas phase reactions in the subnebula or by accretional heating during the formation of Titan. These conclusions can be tested by further studies of abundances and isotope ratios in Titan's atmosphere, augmented by studies of comets. The possible similarity of carbon and nitrogen inventories on Titan to those on the inner planets makes this investigation particularly intriguing.

Ammonia↗
PubMed2003

Analysis of atmospheric behavior of PCDDs/PCDFs by a one-compartment box model.

The overall atmospheric behavior of PCDDs/PCDFs in the Kanto region, Japan, was simulated by a one-compartment box model. For each homologue the relative significance and temperature dependences of dry deposition, wet deposition, degradation, and advection in both gas and particulate phases were examined and compared. The results of the model calculation suggested that the rates for dry deposition are comparable to those for wet deposition, and the rates for advection are comparable to those for bulk (dry+wet) depositions in the Kanto region. On the other hand, the rates of degradation for PCDDs/PCDFs in the atmosphere in the Kanto region would be negligible. The emission rates and the bulk deposition fluxes in the entire Kanto region estimated by the model calculation based on observed air concentrations were 0.084-0.90 kg-TEQ/month and 0.045-0.43 kg-TEQ/month, respectively. These estimated emission rates and bulk deposition fluxes were slightly higher than the estimated emission rate based on observed emission concentrations and the estimated bulk deposition fluxes based on observed deposition fluxes collected on water deposition surface, respectively. This study showed the model calculation can be available for understanding of the overall atmospheric behavior, verification of the source inventory, and estimation of deposition flux on the actual environment including various deposition surfaces.

Air Movements↗
PubMed2003

Degradation mechanism of t-butyl methyl ether (MTBE) in atmospheric droplets.

The aim of this study was to obtain information about the degradation of t-butyl methyl ether (MTBE; (CH(3))(3)C-O-CH(3)) in atmospheric water droplets (rain, clouds, fog). These water droplets contain hydrogen peroxide and iron ions, which are a source of the powerful oxidising radical OH degrees, particularly under solar irradiation (photo-Fenton reaction). MTBE was chosen for this work because of its current use as an oxygenated additive in gasoline. In this study we found that MTBE is not stable in the atmosphere. More than 15 intermediate products were identified, five of which were quantified (t-butyl formate (TBF), methyl acetate (MA), t-butyl alcohol (TBA), acetone (AC), formaldehyde). The evaluation of the disappearance kinetic of the main intermediate compounds shows the following activity pattern k((TBA))>k((MTBE))>k((TBF)),k>((AC)). Acetone was found to be about 15 times more stable than MTBE in atmospheric conditions. The degradation pathways are discussed on the basis of these identifications and on the degradation of the main intermediate products in similar conditions to MTBE.

Air Pollutants↗
PubMed1996

Atmospheric cosmic rays and solar energetic particles at aircraft altitudes.

Galactic cosmic rays, which are thought to be produced and accelerated by a variety of mechanisms in the Milky Way galaxy, interact with the solar wind, the earth's magnetic field, and its atmosphere to produce hadron, lepton, and photon fields at aircraft altitudes that are quite unlike anything produced in the laboratory. The energy spectra of these secondary particles extend from the lowest possible energy to energies over an EeV. In addition to cosmic rays, energetic particles, generated on the sun by solar flares or coronal mass ejections, bombard the earth from time to time. These particles, while less energetic than cosmic rays, also produce radiation fields at aircraft altitudes which have qualitatively the same properties as cosmic rays. The authors have calculated atmospheric cosmic-ray angular fluxes, spectra, scalar fluxes, and ionization, and compared them with experimental data. Agreement with these data is seen to be good. These data have been used to calculate equivalent doses in a simplified human phantom at aircraft altitudes and the estimated health risks to aircraft crews. The authors have also calculated the radiation doses from several large solar energetic particle events (known as GLEs, or Ground Level Events), which took place in 1989, including the very large event known as GLE 42, which took place on September 29th and 30th of that year. The spectra incident on the atmosphere were determined assuming diffusive shock theory. Unfortunately, there are essentially no experimental data with which to compare these calculations.

Aerospace Medicine↗
PubMed2001

Formation of bioorganic compounds in simulated planetary atmospheres by high energy particles or photons.

Various types of organic compounds have been detected in Jupiter, Titan, and cometary coma. It is probable that organic compounds were formed in primitive Earth and Mars atmospheres. Cosmic rays and solar UV are believed to be two major energy sources for organic formation in space. We examined energetics of organic formation in simulated planetary atmospheres. Gas mixtures including a C-source (carbon monoxide or methane) and a N-source (nitrogen or ammonia) was irradiated with the followings: High energy protons or electrons from accelerators, gamma-rays from 60Co, UV light from a deuterium lamp, and soft X-rays or UV light from an electron synchrotron. Amino acids were detected in the products of particles, gamma-rays and soft X-rays irradiation from each gas mixture examined. UV light gave, however, no amino acid precursors in the gas mixture of carbon monoxide, nitrogen and nitrogen. It gave only a trace of them in the gas mixture of carbon monoxide, ammonia and water or that of methane, nitrogen and water. Yield of amino acid precursors by photons greatly depended on their wavelength. These results suggest that nitrogen-containing organic compounds like amino acid precursors were formed chiefly with high energy particles, not UV photons, in Titan or primitive Earth/Mars atmospheres where ammonia is not available as a predominant N-source.

Alanine↗
PubMed2003

Preliminary validation of computational procedures for a new atmospheric ionizing radiation (AIR) model.

A new computational procedure to determine particle fluxes in the Earth's atmosphere is presented. The primary cosmic ray spectrum has been modeled through an analysis of simultaneous proton and helium measurements made on high altitude balloon flights and spacecraft. An improved global fit to the data was achieved through applying a unique technique utilizing the Fokker-Plank equation with a non-linear rigidity-dependent diffusion coefficient. The propagation of primary particles through the Earth's atmosphere is calculated with a three-dimensional Monte Carlo transport program called FLUKA. Primary protons and helium nuclei (alphas) are generated within the rigidity range of 0.5 GV-20 TV uniform in cos2 theta. For a given location, primaries above the effective cutoff rigidity are transported through the atmosphere. Alpha particles are initially transported with a separate package called HEAVY to simulate fragmentation. This package interfaces with FLUKA to provide interaction starting points for each nucleon originating from a helium nucleus. Results from this calculation are presented and compared to measurements.

Alpha Particles↗
PubMed1997

New planetary atmosphere simulations: application to the organic aerosols of Titan.

The atmosphere of Titan partly consists of hazes and aerosol particles. Experimental simulation is one of the powerful approaches to study the processes which yield these particles, and their chemical composition. It provides laboratory analogues, sometimes called tholins. Development and optimization of experimental tools were undertaken in order to perform chemical and physical analyses of analogues under conditions free from contamination. A "Titan aerosol generator" was developed in the frame of the Cassini-Huygens mission, in order to produce Titan's aerosol analogues within conditions closer to those of the titanian atmosphere: cold plasma simulation system, low pressure and low temperature. The direct current (DC) glow discharge is produced by applying a DC voltage between two conductive electrodes inserted into the gas mixture-model of the studied atmosphere- at low pressure. A high-impedance power supply is used to provide the electrical field. All the system is installed in a glove box, which protect samples from any contamination. Finally the research program expected with this new material is presented.

Aerosols↗
PubMed1998

Neutron spectra in the atmosphere from interactions of primary cosmic rays.

Spectra of neutrons from interactions of primary cosmic rays in the earth's atmosphere are calculated with the Monte Carlo model FLUKA for various depths down to sea level. We discuss the environmental models describing the primary cosmic ray spectrum and details of the calculations. Neutron energy spectra are presented for different depths in the atmosphere and for different geographical locations. By comparing results of calculations to measurements on neutron spectra it is shown that FLUKA may serve as an important tool for the estimation of the radiation environment in the atmosphere.

Atmosphere↗
PubMed1998

The atmospheric cosmic- and solar energetic particle radiation environment at aircraft altitudes.

Galactic cosmic rays interact with the solar wind, the earth's magnetic field and hadron, lepton and photon fields at aircraft altitudes. In addition to cosmic rays, energetic particles generated by solar activity bombard the earth from time to time. These particles, while less energetic than cosmic rays, also produce radiation fields at aircraft altitudes which have qualitatively the same properties as atmospheric cosmic rays. We have used a code based on transport theory to calculate atmospheric cosmic-ray quantities and compared them with experimental data. Agreement with these data is seen to be good. We have then used this code to calculate equivalent doses to aircraft crews. We have also used the code to calculate radiation doses from several large solar energetic particle events which took place in 1989, including the very large event that occurred on September 29th and 30th of that year. The spectra incident on the atmosphere were determined assuming diffusive shock theory.

Aerospace Medicine↗
PubMed1995

Formation of bioorganic compounds in planetary atmospheres by cosmic radiation.

Simulated planetary atmospheres (mixtures of simple gases) were irradiated with high energy particles to simulate an action of cosmic rays. When a mixture of carbon monoxide, nitrogen and water was irradiated with 2.8-40 MeV protons, a wide variety of bioorganic compounds including amino acids, imidazole, and uracil were identified in the products. The amount of amino acids was proportional to the energy deposit to the system. Various kinds of simulated planetary atmospheres, such as "Titan type" and "Jovian type", were also irradiated with high energy protons, and gave amino acids in the hydrolyzed products. Since cosmic rays are a universal energy source in space, it was suggested that formation of bioorganic compounds in planetary atmospheres is inevitable in the course of cosmic evolution.

Amino Acids↗
PubMedDate not supplied

The effects of different heat treatment and atmospheres on the NMR signal and structure of TiO2-ZrO2-SiO2 sol-gel materials.

The effects of different heat treatment schemes (i.e. successively or directly heated to particular temperatures) and atmospheres (air or nitrogen) on the solid-state NMR spectra obtained from (TiO(2))(0.15)(ZrO(2))(0.05)(SiO(2))(0.80) sol-gel materials are investigated. A combination of 1H, 13C, 17O and 29Si NMR is used. 29Si MAS NMR indicates that the extent of condensation of the silica-based network strongly depends on the maximum temperature the sample has experienced, but the condensation is largely independent of the details of the heat treatment scheme and atmosphere used. For sol-gel produced silicate-based materials the results show that the equilibrium structure at each temperature is reached rapidly compared to the time (2h) spent at that temperature. The 17O NMR results confirm that a nitrogen atmosphere does significantly reduce loss of 17O from the structure but care must be taken since there could be differential loss of 17O from the regions having different local structural characteristics.

Atmosphere↗