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PubMed2006

Atmospheric field measurements of the hydroxyl radical using laser-induced fluorescence spectroscopy.

The hydroxyl radical, OH, is the most important cleansing agent in the Earth's atmosphere, removing the majority of trace gases by oxidation, including greenhouse gases and CFC replacements. It is intimately involved in the chemistry that generates photochemical smog, which includes many substances harmful to health, such as ozone and particulate matter. In this review, the technique of laser-induced fluorescence for the detection of OH in the atmosphere is described, using as an example the fluorescence assay by gas expansion (FAGE) instrument developed at the University of Leeds. The comparison of measured OH concentrations at a given field site with those calculated by an atmospheric model, which is a mathematical representation of the underlying chemistry, provides one of the best methods to test whether the key chemical and physical processes are understood. Examples are given for field measurements made in clean and polluted environments.

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PubMedDate not supplied

A method for the in vitro exposure of human cells to environmental and complex gaseous mixtures: application to various types of atmosphere.

The application of in vitro methods to the analysis of the effects of airborne materials is still limited, because there are no generally accepted concepts and technologies for efficiently exposing adherent growing cells to test atmospheres, especially those comprising complex mixtures of gaseous and particulate phases. The introduction of in vitro research into the field of inhalation toxicology offers a unique possibility for using human cells and tissues for pre-screening studies, thus reducing the necessity for animal experiments, and cutting the numbers of animals used in toxicological testing. We therefore developed a novel experimental concept that uses an exposure device based on the cell cultivation system CULTEX (Patent No. DE 198011763; PCT/EP99/00295). This allowed us to investigate environmental atmospheres, which were chemically and physically unmodified, in an in vitro system, by exposing the target cells directly at the air/liquid interface. The exposure device itself is small and flexible enough to be connected to a variety of aerosol-generating systems without the need for an incubator, as it fulfils all the requirements for maintaining cell viability over a defined period. The general applicability and the sensitivity of this in vitro approach for testing various generated atmospheres under the same cell-exposure conditions were demonstrated by studying dose-dependent cytotoxic effects in human lung epithelial cells exposed to air contaminated with single gases or complex mixtures, such as diesel exhaust fumes and side-stream cigarette smoke.

Adenosine↗

PubMed2006

Atmosphere, tolerance, and cultural competence in a baccalaureate nursing program: outcomes of a nursing workforce diversity grant.

The purpose of this article is to report the results of a comparison between the educational climate of a baccalaureate nursing program and that of a Nursing Workforce Diversity Grant. Fifteen Hispanic/Latino and American Indian upper-division baccalaureate nursing students completed 37 questionnaires. A 76-item questionnaire was designed to measure the effectiveness of grant services. There was a difference (t [34] = 3.174, p = .003) in satisfaction across the two climates on "caring and respect" and "atmosphere" (t [33] = 3.267, p = .003), with the grant climate rated higher. Although there was overall satisfaction with both the nursing program and grant services, students requested improvements in atmosphere, tolerance, and cultural competency. There is a need to create an atmosphere of trust, caring, and cultural congruity to recruit and to retain diverse students.

Adult↗

PubMed1998

The importance of atmospheric odours for the homing performance of pigeons in the sonoran desert of the southwestern united states

The importance of atmospheric odours for homing pigeon navigation in a desert environment was tested using birds from two lofts located in the Sonoran desert near Tucson, Arizona, USA. When released from a familiar training site, experienced control pigeons and pigeons given intranasal injections of zinc sulphate to produce anosmia both displayed good homeward orientation and homed rapidly. When released from two unfamiliar locations, in contrast, the controls continued to display good homing performance while the zinc-sulphate-treated pigeons homed poorly. Significant differences in vanishing bearings, homing time and homing success were recorded. When a group of control and a group of zinc-sulphate-treated inexperienced pigeons were released from two unfamiliar locations, both groups homed poorly. Nonetheless, the controls still outperformed the zinc-sulphate-treated birds, the most notable result being a significant difference in homing success. Taken together, these results highlight the importance of atmospheric odours for the operation of the navigational map of the homing pigeon in a desert environment and, together with previous experiments, demonstrate that the role of atmospheric odours in homing does not seem to vary in any salient way with ambient climatic conditions.

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PubMed1976

Measurement of some potentially hazardous materials in the atmosphere of rubber factories.

Two separate topics of work are outlined: methods for the measurement of chlorinated monomers in PVC and polychloroprene, and also methods for the measurement of these materials in factory air. Typical results which have been obtained in supplies of raw materials, in finished products, and in the working atmosphere at manufacturing operations are given. The second topic concerns the measurement of benzo[a]pyrene in the atmosphere of a tire manufacturing plant. This material is present in trace quantities in the mineral oils and carbon blacks used by the industry. The atmospheric concentrations present at various processes in this plant were measured on a daily basis over a period of two years, and the results obtained compared with results taken concurrently from an outside air station. It is shown that no significant quantities of benzo[a]pyrene are produced by tire manufacturing operations.

Air Pollutants↗

PubMed1978

Plants as bioassay systems for monitoring atmospheric pollutants.

Plant species act as natural bioindicators of atmospheric pollutants. Plants can be used as bioassay systems for monitoring atmospheric pollutants. Plant injury symptoms, altered growth and reproductive pattern, changes in yield and/or productivity, and changes in species distribution can be used singly or in combination as monitoring devices. The results must be accepted as semiquantitative, but within that constraint, air quality can be sufficiently well defined to enable the setting of air quality standards. Genetic variability of higher plant species has yielded cultivars which display a range of tolerance to gaseous and particulate atmospheric pollutants. Asexual propagation of these cultivars provides pollutant-sensitive and pollutant-tolerant plant material which can be grown on selected sites for observation. Gymnosperm and Angiosperm species as well as species of lichens and mosses have been used to establish field monitoring networks in Europe, Canada, and the United States. White pine, shade tobacco, mosses, and lichens have proven particularly useful as bioassay tools. Pollen from pollutant-sensitive and pollutant-tolerant plant cultivars has also been used as a sensitive laboratory bioassay tool for studying air quality. Epiphytic mosses are particularly efficient as monitors of particulate pollutants, especially heavy metals, some of which may act as chemical mutagens. The cost, complexity, and lack of reliability of instrumented systems for air quality monitoring make imperative the need to develop successful plant bioassay systems for monitoring air quality.

Air Pollutants↗

PubMed1983

Formation and fate of gaseous and particulate mutagens and carcinogens in real and simulated atmospheres.

The growing use of coal for heating and electric power generation and diesel engines in light duty motor vehicles will increase not only the existing atmospheric concentrations of criteria pollutants such as NO2, SO2, O3 and fine particulates, but also the concentrations of a number of highly reactive gaseous copollutants such as HONO, HONO2, PAN and the nitrate radical, NO3. These gaseous noncriteria pollutants are of interest not only because of their roles in the chemistry of the "clean" and polluted troposphere, including "acid rain," but also because they may pose health risks disproportionate to their relatively low ambient concentrations, and through complex heterogeneous reactions, they may serve as precursors or catalysts in the formation of "nonclassical" particulate mutagens and carcinogens such as certain nitroarenes associated with combustion generated particulate polycyclic organic matter (POM). Results of research efforts to establish current ambient levels of these noncriteria pollutants and to develop an understanding of their sources, formation and sinks are reported here. First, long pathlength (greater than or equal to 1 km) infrared and UV-visible spectroscopic studies of ambient levels of gaseous HONO, NO3, HONO2, PAN, HCHO and HCOOH in southern California atmospheres are described, and data given on their ambient concentrations. Second, an integrated chemical/microbiological investigation is described. It is directed toward identifying the nature of direct-acting mutagens found in extracts of diesel and ambient POM, as well as those formed upon exposure of environmentally relevant PAH to simulated natural and polluted atmospheres. The identification of certain of these mutagens, including a newly identified class of mutagenic PAH-lactones is discussed, along with the mechanisms of their formation and fate in the natural and polluted troposphere.

Air Pollutants↗

PubMed2002

Piffalls in atmospheric correction of ocean color imagery: how should aerosol optical properties be computed?

Current methods for the atmospheric correction of ocean-color imagery rely on the computation of optical properties of a mixture of chemically different aerosol particles through combination of the mixture with it into an effective, single-particle component that has an average refractive index. However, a multi-component approach in which each particle type independently grows and changes its refractive index with increasing humidity is more realistic. Computations based on Mie theory and radiative transfer are used to show that the two approaches result in top-of-the-atmosphere radiances that differ more than the water-leaving radiance. Thus, proper atmospheric correction requires a multicomponent approach for the computation of realistic aerosol optical properties.

Journal Article↗

PubMed2002

Comment on "Heterodyne lidar returns in the turbulent atmosphere: performance evaluation of simulated systems".

The explanation proposed by Belmonte and Rye [Appl. Opt. 39, 2401 (2000)] for the difference between simulation and the zero-order theory for heterodyne lidar returns in a turbulent atmosphere is incorrect. The theoretical expansion the authors considered is not developed under a square-law structure-function approximation (random-wedge atmosphere). Agreement between the simulations and the zero-order term of the theoretical expansion is produced for the limit of statistically independent paths (bistatic operation with large transmitter-receiver separation) when the simulations correctly include the large-scale gradients of the turbulent atmosphere.

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PubMed2002

Balloonborne calibrated spectroradiometer for atmospheric nadir sounding.

Laboratoire de Physique Moléculaire et Applications (LPMA)/Infrared Atmospheric Sounding interferometer (IASI) balloon is a calibrated infrared Fourier transform spectrometer that is used to measure the Earth's atmospheric emission (650-3000 cm(-1)). Operating under a stratospheric balloon, this spectroradiometer provides radiometrically calibrated spectra with an apodized spectral resolution of 0.1 cm(-1), which can be used to retrieve the concentration of atmospheric trace gases such as H2O, CO2, CO, O3, N2O, and CH4. The radiometric calibration is performed by use of two reference blackbodies. A reference cavity (LPMA blackbody) has been developed to validate the radiometric calibration procedure and to characterize the instrument performances. One goal of the LPMA/IASI balloon is the preparation of the IASI mission, which is a satellite instrument dedicated primarily to operational meteorology. A description of the LPMA/IASI balloon, its performances, and the results obtained during the first flight of the instrument are presented.

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PubMed2003

Ray tracing and refraction in the modified US1976 atmosphere.

A new and flexible ray-tracing procedure for calculating astronomical refraction is outlined and applied to the US1976 standard atmosphere. This atmosphere is generalized to allow for a free choice of the temperature and pressure at sea level, and in this form it has been named the modified US1976 (MUSA76) atmosphere. Analytical expressions and numerical procedures are presented for calculating dry-air refractions and for the water-vapor correction. Results for all apparent altitudes are presented and compared with The Star Almanac for Land Surveyors (1951), The Nautical Almanac (1958), and the Pulkovo tables (Refraction Tables of the Pulkovo Observatory, 1985). Dependences on sea-level pressure, temperature, and temperature gradient and on humidity are discussed.

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PubMed2003

Atmospheric correction of SeaWiFS imagery for turbid coastal and inland waters: comment.

Ruddick et al. [Appl. Opt. 39, 897 (2000)] extended the standard SeaWiFS atmospheric-correction algorithm for use over turbid coastal and inland waters. However, Ruddick's method is based on the assumption of a spatially homogeneous constant ratio for the water-leaving reflectances normalized by the sun-sea atmospheric transmittance at 765 and 865 nm. Such first-order b(b)/a model-based assumption can result in an inaccuracy for highly turbid water. Using the first- and second-order b(b)/(a + b(b)) models as well as the second-order b(b)/a model (which, more realistically, do not assume spatial homogeneity ratio), we suggest using the modified assumption, R(8)(-1) = alpha0 R(7)(-1) + (l1Q)(-1) (1 - alpha0), instead of Ruddick's assumption, in SeaWiFS atmospheric-correction algorithms for highly turbid waters.

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PubMed2003

Spaceborne estimate of atmospheric CO2 column by use of the differential absorption method: error analysis.

For better knowledge of the carbon cycle, there is a need for spaceborne measurements of atmospheric CO2 concentration. Because the gradients are relatively small, the accuracy requirements are better than 1%. We analyze the feasibility of a CO2-weighted-column estimate, using the differential absorption technique, from high-resolution spectroscopic measurements in the 1.6- and 2-microm CO2 absorption bands. Several sources of uncertainty that can be neglected for other gases with less stringent accuracy requirements need to be assessed. We attempt a quantification of errors due to the radiometric noise, uncertainties in the temperature, humidity and surface pressure uncertainty, spectroscopic coefficients, and atmospheric scattering. Atmospheric scattering is the major source of error [5 parts per 10 (ppm) for a subvisual cirrus cloud with an assumed optical thickness of 0.03], and additional research is needed to properly assess the accuracy of correction methods. Spectroscopic data are currently a major source of uncertainty but can be improved with specific ground-based sunphotometry measurements. The other sources of error amount to several ppm, which is less than, but close to, the accuracy requirements. Fortunately, these errors are mostly random and will therefore be reduced by proper averaging.

Journal Article↗

PubMed2003

Atmospheric turbulence characterization with the Keck adaptive optics systems. I. Open-loop data.

We present a detailed investigation of different methods of the characterization of atmospheric turbulence with the adaptive optics systems of the W. M. Keck Observatory. The main problems of such a characterization are the separation of instrumental and atmospheric effects and the accurate calibration of the devices involved. Therefore we mostly describe the practical issues of the analysis. We show that two methods, the analysis of differential image motion structure functions and the Zernike decomposition of the wave-front phase, produce values of the atmospheric coherence length r0 that are in excellent agreement with results from long-exposure images. The main error source is the calibration of the wave-front sensor. Values determined for the outer scale L0 are consistent between the methods and with typical L0 values found at other sites, that is, of the order of tens of meters.

Journal Article↗

PubMed2003

Long-path measurement of atmospheric NO2 with an obstruction flashlight and a charge-coupled-device spectrometer.

A novel method of differential optical absorption spectroscopy (DOAS) is proposed and demonstrated to monitor the concentration of atmospheric pollutant gas. In contrast to conventional DOAS measurements with continuous light sources, the present method relies on white flashlights such as aviation obstruction lights that are generally installed on tall constructions. A simple detection system is devised by means of a telescope and a compact CCD spectrometer. A path length of 5.5 km allows us to measure atmospheric NO2 concentration with a detection limit of approximately 1 part per billion. We also discuss the possibility of deriving the aerosol optical thickness through the horizontal atmosphere from this pulsed DOAS measurement.

Journal Article↗

PubMed2005

Directional variation of visual range due to anisotropic atmospheric brightness.

The meteorological optical range (MOR) is the greatest distance at which a nonluminous object is barely discernible. Koschmieder related the optical atmospheric extinction coefficient to the contrast between the object and its background. His law assumes a uniform atmosphere and yields an isotropic value of the MOR. The model presented here incorporates the effect of anisotropic atmospheric brightness on contrast (and thus on the MOR). The Koschmieder MOR is then decreased by a factor according to the brightness prevailing in the direction of assessment. Manual assessments of the MOR made in arbitrary directions are shown to agree satisfactorily with the derated MOR. Minor modifications to existing instruments at airports would enable the instruments to register true values of the MOR and the runway visual range in directions relevant to the pilot, i.e., along the runway.

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PubMed2005

Retrieval of vertical constituents and temperature profiles from passive submillimeter wave limb observations of the Martian atmosphere: a feasibility study.

The investigation of the Martian atmosphere is of key importance for an understanding of the planets present and past. Passive limb observations of thermal radiation at submillimeter wavelengths in the 320-350-GHz range by use of a state-of-the-art satellite receiver on a low Mars orbit allow important parameters such as the mixing ratios of H2O, HDO, 12CO, 13CO, O3, and H2O2 as well as the thermal profile to be retrieved with high precision and unprecedented vertical range and resolution, providing valuable information for better understanding of the planet's water cycle, atmospheric dynamics, and photochemistry. The feasibility of these kinds of measurement is demonstrated by means of model simulations based on realistic atmospheric, spectroscopic, and instrumental parameters. Temperature can be retrieved to approximately 90 km with half-scale height vertical resolution from single-scan measurements of emission lines of the long-lived species 12CO and 13CO. The global water-vapor distribution can be measured even under dry or wet conditions with good vertical resolution from the surface to approximately 45 km, and simultaneous observations of HDO allow useful information on the D/H ratio up to an altitude of approximately 30 km to be derived. The sensitivity of the limb-sounding technique also permits information on the photochemically important minor species O3, and H2O2 to be obtained. It is shown that spectral averaging may improve precision, altitude range, and resolution of the retrieved profiles. Other frequency bands are explored, and the 435-465-GHz range is suggested as a possible alternative to the 320-350-GHz range.

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PubMed2005

Atmospheric refraction: a history.

We trace the history of atmospheric refraction from the ancient Greeks up to the time of Kepler. The concept that the atmosphere could refract light entered Western science in the second century B.C. Ptolemy, 300 years later, produced the first clearly defined atmospheric model, containing air of uniform density up to a sharp upper transition to the ether, at which the refraction occurred. Alhazen and Witelo transmitted his knowledge to medieval Europe. The first accurate measurements were made by Tycho Brahe in the 16th century. Finally, Kepler, who was aware of unusually strong refractions, used the Ptolemaic model to explain the first documented and recognized mirage (the Novaya Zemlya effect).

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