Showing papers on "Haze published in 1997"

Results from the Mars Pathfinder camera.

Abstract: Images of the martian surface returned by the Imager for Mars Pathfinder (IMP) show a complex surface of ridges and troughs covered by rocks that have been transported and modified by fluvial, aeolian, and impact processes. Analysis of the spectral signatures in the scene (at 440- to 1000-nanometer wavelength) reveal three types of rock and four classes of soil. Upward-looking IMP images of the predawn sky show thin, bluish clouds that probably represent water ice forming on local atmospheric haze (opacity ∼0.5). Haze particles are about 1 micrometer in radius and the water vapor column abundance is about 10 precipitable micrometers.

Detection of volcanic ash clouds from Nimbus 7/total ozone mapping spectrometer

Abstract: Measured radiances from the Version 7 reprocessing of the Nimbus 7/total ozone mapping spectrometer (TOMS) 340- and 380-nm channels are used to detect absorbing particulates injected into the atmosphere after the El Chichon eruption on April 4, 1982. It is shown that while the single-channel reflectivity determined from the 380-nm channel is able to detect clouds and haze composed of nonabsorbing aerosols, the spectral contrast between the 340- and 380-nm channels is sensitive to absorbing particulates such as volcanic ash, desert dust, or smoke from biomass burning. In this paper the spectral contrast between these two channels is used to detect the volcanic ash injection into the atmosphere and to track its evolution for several days. The movement of the ash clouds is shown to be consistent with the motions expected from the National Centers for Environmental Prediction (NCEP)-derived balanced wind fields in the troposphere and lower stratosphere. The movement of the volcanic SO2 cloud detected from TOMS data was also in agreement with the NCEP wind at higher altitudes of up to 100–10 mbar. The vertical wind shear in the neighborhood of the eruption site resulted in a clear separation of the ash and SO2 clouds. The location and movement of the ash cloud are consistent with information obtained by the advanced very high resolution radiometer (AVHRR) instrument on board the NOAA 7 satellite and to ground reports of ash fall.

Haze and cloud in apple juices

Abstract: Turbidity in apple juice is desirable or undesirable, depending on whether the product fits within consumer expectations. Desirable opalescence is due to soluble pectin and insoluble pectin stabilized particles that show considerable stability. Blanching treatments enhance this stability by reducing particle size and character-solubilizing pectin, and possibly by the destruction of natural enzymes that may destabilize the cloud over time. Undesirable haze and sediments may arise in apple juice by several mechanisms, including starch (dextrin) retrogradation, protein phenol aggregation, phenol oxidation, crystallization of carbohydrate macromolecules extracted from cell walls, or difficulties during manufacture. The mechanisms of formation of each of these forms of haze are discussed and examples given form the literature. Where available, haze-sediment morphology by light and/or electron microscopy is documented and the possible role of recently developed "macerase" enzymes in haze/sediment formation discussed.

Constraints on using AVHRR composite index imagery to study patterns of vegetation cover in boreal forests

Abstract: A wide range of techniques are being developed to map vegetation cover types using multi-date imagery from the Advanced Very High Resolution Radiometer. To date, these techniques do not account for severe constraints which exist for the world's boreal forest. Using composite AVHRR imagery collected over Alaska, we demonstrate how several factors influence the time-series normalized vegetation difference index (NDVI) signatures developed for the boreal forests in this region, including the effects of: (1) clouds and atmospheric haze; (2) climate variations on plant phenology; (3) fire on forest succession; and (4) forest stand patch size with respect to system resolution. Based on the analysis of AVHRR composite data from Alaska, the results of this study show: (1) clouds and haze have distinct effects on the intra-seasonal NDVI signature; (2) there are significant interseasonal variations in NDVI signatures caused by variations in the length of the growing season as well as variations in precipit...

Observed Dependencies of Atmospheric UV Radiation and Trends

Abstract: The intensity of solar UV-B radiation incident on the Earth’s surface at a given wavelength is dependent on many atmospheric variables. These variables include the column amount and the vertical distribution of ozone, the thickness and distribution of cloud cover, aerosol content and pollution. Other variables include the zenith angle of the sun, the altitude above sea level and the albedo of the Earth’s surface. It is possible to distinguish between some of the different influences using a detailed analysis of the wavelength dependence of the observed radiation incident at the Earth’s surface. Consideration of the wavelength dependence of long-term changes in UV radiation identify the extent to which long-term changes in different atmospheric variables contribute to any observed trends. Examples of the behaviour of spectral UV radiation with respect to different variables such as sun angle, ozone, clouds and haze will be presented.

Droplet Concentration and Size Distribution in Haze and Fog

Abstract: Fog (haze) droplet concentrations and size distributions were measured at five sampling sites representing rural and urban regions and a highly polluted marine-urban environment. Droplet imprints in a thin gelatine layer were evaluated and compared to the measurement by light scattering instruments. This enabled conditions for the application of the logarithmic-normal size distribution and for the classification of typical fog droplet size distributions to be established. In particular, the parameters featuring the width and asymmetry of a size distribution were suggested and calculated. Advantages and drawbacks of the applied droplet sampling and evaluation technique are discussed in more detail.

The Development of a Model to Examine Source-Receptor Relationships for Visibility on the Colorado Plateau.

Abstract: This paper describes the development and application of the Visibility and Haze in the Western Atmosphere (VISHWA) model to understand the source-receptor relationships that govern chemical species relevant to visibility degradation in the western United States. The model was developed as part of a project referred to as Visibility Assessment for Regional Emission Distributions (VARED), the objective of which is to estimate the contributions of various geographical regions, compounds, and emission sources to light scattering and absorption by particles on the Colorado Plateau. The VISHWA model is a modified version of a comprehensive Eulerian model, known as the Acid Deposition and Oxidant Model.1 The modifications were designed to obtain the computational efficiency required to simulate a one-year period at about 1/25th of real time, and at the same time incorporate mechanistic features relevant to realistic modeling of the fate and transport of visibility degrading species. The modifications included use of a condensed chemical mechanism; incorporation of reactions to simulate the formation of secondary organic particles; and use of a semi-Lagrangian advection scheme to preserve concentration peaks during advection. The model was evaluated with 1992 air quality data from Project MOHAVE (Measurements of Haze and Visual Effects) intensive experiments. An important conclusion of this evaluation is that aqueous-phase oxidation of SO2 to sulfate in nonprecipitating clouds makes a significant contribution to observed sulfate levels during winter as well as summer. Model estimates of ambient sulfate for the winter intensive were within a factor of 2 of the observations for 75% of the values. The corresponding statistic for the summer intensive was 90%. Model estimates of carbon were within a factor of 2 of the limited set of observations.

A biwavelength analysis of Pioneer Venus polarization observations

Abstract: A new method for analyzing Pioneer Venus polarimetry data on a pixel-wise basis is presented. Quasi-simultaneous observations at two wavelengths (550 and 935 nm) are combined and compared with results of multiple scattering calculations. In this manner, hypotheses about particle size distributions in the upper part of the Venus atmosphere are tested. Particles composed of a sulfuric acid solution are considered, and a distinction is made between large and small particles, called cloud and haze particles, respectively. Three model atmospheres have been investigated: (1) a single layer containing cloud particles, (2) a single layer containing a mixture of cloud and haze particles, and (3) a two layer model with an upper layer composed of haze particles and a lower layer containing cloud particles. It is found that all three models agree with the observations at phase angles near 20°, but that the first model cannot be made to agree with the observations for phase angles near 90°. This confirms the presence of haze particles in the Venus atmosphere found earlier by Kawabata et al. [1980]. We find that the haze particles may be situated either above or mixed within the main cloud deck of Venus. We derived effective radii between 0.85 and 1.15 μm for the cloud particles, and effective radii of 0.2 or 0.3 μm for the haze particles. When the haze particles are situated above the cloud layer, the haze optical thickness can take values of up to 0.6 at 550 nm. When the haze particles are mixed with the cloud particles, their contribution to the total atmospheric scattering coefficient at 550 nm can become as large as 70%.

Cloud multi-phase processes and high alpine air and snow chemistry : ground-based cloud experiments and pollutant deposition in the high Alps

Abstract: I Ground-Based Cloud Experiments (GCE).- 1 GCE: an Overview.- 1.1 Introduction.- 1.2 Overview of the Three GCE Joint Field Experiments.- 2 Principal Results from GCE.- 2.1 Size Distribution, Hygroscopic Properties and Chemical Composition of Aerosol Particles.- 2.2 Nucleation Scavenging.- 2.3 Other in-Cloud Particle Scavenging Processes.- 2.4 Scavenging of Gases.- 2.5 Cloud Droplet Liquid-Phase Chemistry and its Dependence on Cloud Microphysics.- 2.6 Effect of Entrainment on Cloud Chemistry and Microphysics.- 2.7 Evaporating Clouds.- 2.8 Cloud Droplet Deposition.- 2.9 Instrument Development and Testing within GCE.- 3 GCE in Retrospective.- 3.1 Meeting the Original Goals of GCE.- 3.2 The Importance of Integrated Field Work, Instrumental Development and Modelling.- 3.3 Airborne Measurements as a Complement to Ground-Based Investigations.- 3.4 Joint Evaluation and Dissemination of GCE Results.- 4 Future Directions for Cloud Research.- 4.1 Effect of Anthropogenic Activity on Aerosol Population.- 4.2 Haze.- 4.3 The Ice Phase of Clouds.- 4.4 Oxidised Nitrogen Chemistry.- 4.5 Organic Chemistry within Clouds.- 4.6 Clouds and Oxidising Capacity of the Atmosphere.- 4.7 Radiative Properties of Clouds.- 4.8 Instrumentation Needs for the Future.- 4.9 Need for Aircraft Measurements.- 5 Individual Reports from GCE Principal Investigators.- 5.1 Field and Wind Tunnel Experiments in Clouds and Fog by ECN.- 5.2 Study of Interstitial Aerosol.- 5.3 Formation and Reactivity of Aerosols.- 5.4 Field and Modelling Studies of Cloud Chemical Processes.- 5.5 The Multiphase Chemistry of Clouds and Fog.- 5.6 A Single Particle Approach to Characterising Droplet Residues and Interstitial Particles.- 5.7 Partitioning of Aerosol Particles Between Droplets and Interstitial Air.- 5.8 Influence of the Chemical Composition of the Atmospheric Particles on Fog and Cloud Formation.- 5.9 The Dynamic Behaviour of Pollutants in Fog and Captive Clouds.- 5.10 The Role of Nitrophenols in Cloud Chemistry.- 5.11 A Droplet Aerosol Analysing System for Cloud Studies.- 5.12 Study of the Interaction of Photo-oxidants and Acidic Components between Gas and Liquid Phase.- 5.13 Input of Trace Substances to High Elevation Forests by Cloud Water Interception.- 6 GCE Publications 1990-1996.- II High Alpine Air and Snow Chemistry.- 7 An Overview of ALPTRAC Research.- 7.1 Introduction.- 7.2 Some Observations and Trends in High Alpine Pollution.- 8 Aims and Internal Structure of ALPTRAC.- 9 Principal Scientific Results.- 9.1 Pollution Levels in High Alpine areas.- 9.2 Seasonal Changes in Pollution Levels.- 9.3 Mechanisms: Chemical Transformation and Scavenging.- 9.4 Transport Processes and Source Areas.- 9.5 Long-Term Trends.- 9.6 Instrumentation Developments.- 9.7 Conclusions.- Individual Reports from ALPTRAC Principal Investigators.- 10 High Alpine Snow Pack Chemistry.- 10.1 Accumulation of Pollutants and Nutrients in the Snow Pack at High Altitudes along a North-South Transect in the Eastern Alps.- 10.2 Stable Isotope Ratio of Sulfur, Nitrogen and Carbon as Pollution Tracers for Atmospheric Constituents.- 10.3 Accumulation of Acidic Components in Two Snowfields in the Sonnblick Region.- 11 Long-Term Pollution Trends.- 11.1 Retrospective and Present State of Anthropogenic Aerosol Deposition at a High Altitude Alpine Glacier (Colle Gnifetti, 4450 m a.s.l.).- 12 High Alpine Air, Aerosol and Cloud Chemistry.- 12.1 Segregation of Hydrometeors.- 12.2 Transport, Scavenging and Deposition Studies of Air Pollutants at High-Alpine Sites.- 12.3 Alpine Aerosol and Snow Chemistry Study at the Sonnblick Observatory (Austria, 3106 m a.s.1.).- 12.4 Aerosol and Hydrometeor Concentrations and their Chemical Composition during Winter Precipitation along a Mountain Slope (Mt. Rigi, Switzerland).- 13 Meteorological Support to ALPTRAC.- 13.1 Meteorological Support Study.- 14 ALPTRAC Publications 1988-1996.- Suject Index.

Atmospheric Ultraviolet Radiation Scattering and Absorption

Abstract: Molecular scattering and absorption by atmospheric gases generally is a wavelength-dependent process. In the UV-B region of the solar spectrum the main gases of the atmosphere, composed primarily of Nitrogen, Oxygen, and some of the rare noble gases are non-absorbing. They do, however, scatter radiation in a process that is named after Lord Rayleigh. The term elastic scattering is often used to indicate that all of the incident radiation intercepted by a non-absorbing molecule is redirected into other directions i.e. there is no loss of radiation to the molecule. The process is wavelength-dependent and goes as the reciprocal of the fourth power of the wavelength. This means that the scattering becomes stronger at the shorter wavelengths. Hence, the reason for a blue sky because the visible wavelengths of the rainbow colors in the sun’s spectrum are so weakly scattered that they are obscured by the strong blue color. However, aerosols (dust) are composed of much larger particles on the order of the wavelength of light compared to the size of air molecules and these particles do not possess strong wavelength-dependent scattering characteristics. Therefore, when aerosols or clouds are present, one often sees a whitish haze or a white cloud because the rainbow colors are mixed more equally. A strongly absorbing haze, however, may take on a darker appearance and might be seen as a brown cloud.

Radiative Effects of Aerosols

Abstract: During the Atlantic Stratocumulus Transition Experiment (ASTEX) in June 1992, two descents in cloud-free regions allowed comparison of the change in aerosol optical depth as determined by an onboard total-direct-diffuse radiometer (TDDR) to the change calculated from measured size resolved aerosol microphysics and chemistry. Both profiles included pollution haze layer from Europe but the second also included the effect of a Saharan dust layer above the haze. The separate contributions of supermicrometer (coarse) and submicrometer (fine) aerosol were determined and thermal analysis of the pollution haze indicated that the fine aerosol was composed primarily of a sulfate/water mixture with a refractory soot-like core.

Method of manufacturing a color display device comprising color-filter layers

Abstract: In the manufacture of a color-display device comprising color-filter layers, phosphor haze may occur. Said phosphor haze adversely affects the picture quality. Phosphor haze can be reduced substantially, or precluded, by providing one, and only one, of the color-filter layers by means of a negative lithography process and, subsequently, providing the phosphor corresponding to this color-filter layer before the other phosphor layers.

On the representation of partial spatial information in knowledge bases

Abstract: A fundamental requirement of advanced spatial applications is the capacity to deal with partial spatial information and multiple levels of granularity. This thesis studies the problem of representing and reasoning with partial spatial information in the context of knowledge bases. The thesis proposes a representation which views space as a totality of objects surrounded by a haze area and interrelated in terms of qualitative spatial relations. The most elementary object type in this representation, is the haze point. This is a non-zero sized object that is associated with an area of haze such that the point in question may be located anywhere inside it. Haze points are related in terms of an indistinguishability (called haze) or an order relation. The notion of haze can help us model situations where information is imprecise; the size of the haze area accounts for the degree of precision. In the course of our study we present a formal axiomatization of the first-order theory of one-dimensional haze point space and develop several extensions of the theory for high dimensional space. We then define a set of topological and directional binary spatial relations in terms of the haze and order primitive relations and formalize spatial inferencing in a setting of varying degree of precision, as a constraint reasoning problem. Our reasoning algorithms make use of a data structure called haze-order graph which allows trading space for efficiency. Experimental results illustrate the efficiency of the proposed algorithms. Finally, we use these results in the development of a spatial data model which facilitates the representation of and reasoning with various forms of qualitatively and quantitatively incomplete spatial information, including indeterminate objects, multiple scales and granularity.

Haze Generation on Silicon Surface Heated in Hydrogen Ambient at Atmospheric Pressure

Abstract: The change in surface roughness of a silicon wafer with temperature is studied using a dry system composed of quartz parts, a small silicon carbide part, a lamp-heating module, and hydrogen ambient at atmospheric pressure. A large diameter silicon wafer having a large temperature gradient is heated at 850 to 1100°C. Haze appears on the silicon surface and shifts from the higher temperature region to the lower temperature region of the wafer with increasing wafer temperature and finally disappears at temperatures higher than 1000°C. The temperature range in which the haze is generated due to surface pit formation is shown to be 900 to 1000°C. The influence of moisture in the gas phase on haze generation is considered to be very small. The surface pit formation is essentially due to the difference between the etch rates of silicon and silicon dioxide by hydrogen gas.

Spatial disaggregation of spectral data for haze assessment in an arid environment

Abstract: A new approach has been introduced to measure statistically haze as generated by dust particles in the atmosphere in an arid area. By using Landsat-5 Thematic Mapper data in an optical waveband, it has been demonstrated that spatial disaggregation of the area under study is logically desirable and practically feasible. The approach essentially requires a reference data set acquired in hazefree conditions. The output is restricted to only the overall haze estimates.

Winter dust haze in tropical southern Africa

Abstract: Dust haze spreads over most of tropical southern Africa in winter, from May to October, with a maximum in July and August over the Zaire Basin. Its origin is primarily biomass burning and secondarily soil deflation, which greatly increases during the dry season. It is mobilized on the continent by the unstable atmospheric boundary layer up to the inversion in the Indian trade wind at about 2000 m altitude. Then it is stretched north-westward by the trade wind and accumulates in the mid-troposphere over the Zaire Basin and the Congo Republic. It is carried away over the Atlantic Ocean from the coast of those countries. It begins to disappear only when synoptic-scale flow patterns change in September. Measures of atmospheric pollution due to biomass burning over the African continent and of atmospheric aerosols above the Atlantic Ocean confirm these results. ©1997 by the Royal Meteorological Society Int. J. Climatol. 17: 725–744, 1997. (No. of Figures: 10. No. of Tables: 1. No. of Refs: 52.)

Malaysia backs ‘gag’ on haze scientists

Abstract: london The Malaysian government has justified a ban on scientists at public institutions talking to the press about the haze from Indonesian forest fires.