Showing papers on "Haze published in 1996"

Detection of biomass burning smoke from TOMS measurements

Abstract: A 145 year gridded data set of tropospheric absorbing aerosol index was derived from the Nimbus-7 Total Ozone Mapping Spectrometer (TOMS) reflectivity difference between 340 and 380 nm channels Based upon radiative transfer calculations, the reflectivity anomaly between these two UV wavelength channels is very sensitive to smoke and soot aerosols from biomass burning and forest fires, volcanic ash clouds as well as desert mineral dust We demonstrate the ability of the TOMS instrument to detect and track smoke and soot aerosols generated by biomass burning in South America TOMS data can clearly distinguish between absorbing particles (smoke and dust) and non-absorbing aerosols (clouds and haze) For South American fires, comparisons of TOMS data are consistent with the limited amount of ground-based observations (Porto Nacional, Brazil) and show generally good agreement with other satellite imagery TOMS data shows large-scale transport of smoke particulates generated by the burning fires in the South America, which subsequentially advects smoke aerosols as far as the Atlantic Ocean east of Uruguay

Effects of clouds and haze on UV‐B radiation

Abstract: An experiment was conducted over a 6-month period in Research Triangle Park, North Carolina, to investigate the effects of clouds and haze on ultraviolet (UV) radiation. Data were collected using a Yankee Environmental Systems UVB-1 pyranometer, an Eppley Laboratory Precision Spectral Pyranometer, and a SCI-TEC Brewer spectrophotometer. Hourly reports of total cloud cover and surface observations of air temperature, dew point temperature, barometric pressure, and visibility from the National Weather Service located at the nearby Raleigh-Durham International Airport were also used in this study. An empirical relationship has been formulated for UV-B attenuation as a function of total solar transmissivity and cloud cover. Cumulus-type clouds were found to attenuate up to 99% of the incoming UV-B radiation during overcast conditions. However, these same clouds were found to produce localized increases of UV-B radiation of up to 27% over timescales less than 1 hour under partly cloudy skies when the direct solar beam was unobstructed. Summer haze was found to attenuate UV-B radiation in the range of 5% to 23% when compared to a clear day in the autumn. In general, total radiation was attenuated more than UV-B radiation under cloudy conditions.

The great dry fog of 1783

Abstract: A persistent dry haze hung over Europe during the second half of 1783. Spawned by the Laki basalt fissure eruption in southern Iceland, this fog evoked much contemporary written commentary, from which the course of events is here reconstructed in a quantitative way. It was the densest European dry fog since the late Middle Ages, and it lay primarily in the troposphere. Spreading broadly toward the south and east, it nevertheless remained mostly confined to the North Atlantic, western Eurasia, and the Arctic. Previously it was believed by many to have risen to the middle stratosphere and to have blanketed much of North America. Composed of sulfuric-acid aerosols, its total mass reached about 200 megatons, as determined from its observed optical thickness. Several authors have pointed out that it may have been responsible for the cold winter of 1783–84, which caused much economic and social distress in many parts of the Northern Hemisphere. As the earliest dry fog to be studied scientifically, it remains the paradigm even today and poses an interesting challenge to climate modelers.

Vertical profiles, aerosol microphysics, and optical closure during the Atlantic Stratocumulus Transition Experiment: Measured and modeled column optical properties

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 a 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 sootlike core. The soot core increased the calculated extinction by about 10% in the most polluted drier layer relative to a pure sulfate aerosol but had significantly less effect at higher humidities. A 3-km descent through a boundary layer air mass dominated by pollutant aerosol with relative humidities (RH) 10–77% yielded a close agreement between the measured and calculated aerosol optical depths (550 nm) of 0.160 (±0.07) and 0.157 (±0.034), respectively. During descent the aerosol mass scattering coefficient per unit sulfate mass (inferred) varied from about 5 to 16 m2 g−1 and was primarily dependent upon ambient RH. However, the total scattering coefficient per total fine mass was far less variable at about 4 ± 0.7 m2 g−1. A subsequent descent through a Saharan dust layer located above the pollution aerosol layer revealed that both layers contributed similarly to aerosol optical depth. The scattering per unit mass of the coarse aged dust was estimated at 1.1 ± 0.2 m2 g−1. The large difference (50%) in measured and calculated optical depth for the dust layer exceeded estimated measurement uncertainty (12%). This is attributed to inadequate data on the spatial variability of the aerosol field within the descent region, a critical factor in any validation of this type. Both cases demonstrate that surface measurements may be a poor indicator of the characteristics and concentration of the aerosol column.

Acidic Gases (HCl, HF, HN03, HCOOH, and CH3COOH): A Review of Ice Core Data and Some Preliminary Discussions on their Air-Snow Relationships

Abstract: In spite of their relative remoteness, the atmosphere of the poloar region is already disturbed by human activities. The development of the so called ″ozone hole″ over Antarctica in spring and the Arctic haze in winter represent good examples of the fragility of these remote atmospheres. One interesting characteristic of these high latitute regions lies in solid precipitation which has been accumulating over polar ice caps for the last several hundred thousands years. Assuming a sufficient knowledge of the relation lingking the composition of the snow and that of the atmosphere at the deposition, ice cores extented from Grrenland and Antractica offer a unique possibility to reconstruct the chemical composition of our pre-industrial atmosphere. They can also help to investigate the variability of our natural atmosphere over time periods as long as several thousands of years.

Method and apparatus for determining ambient conditions from an image sequence, such as fog, haze or shadows

Abstract: A method and apparatus for determining certain ambient conditions in a scene by analyzing a sequence of images that represent the scene. The apparatus uses only image information to determine scene illumination, or the presence of shadows, fog, smoke, or haze by comparing properties of detected objects, averaged over a finite video sequence, against properties of the reference image of the scene as that scene would appear without any objects present. Such a reference image is constructed in a manner similar to time-averaging successive camera images.

The impacts of SO2 oxidation in cloud drops and in haze particles on aerosol light scattering and CCN activity

Abstract: Calculations with an explicit microphysical model show significant sulfate production in both clouds and unactivated haze but significant impact on particle light scattering and CCN production only for the cloud scenarios.

The chemical mass balance method for estimating atmospheric particle sources in southern california

Abstract: The greater Los Angeles metropolitan area (the South Coast Air Basin) historically has had a severe air pollution problem whose visible symptom is a dense smoke-like haze mixed with fog (smog). More than 25 years ago, Friedlander and his associates began attempts to characterize the detailed chemistry of smog particles, and to interpret these results in terms of source emissions. Source apportionment was formalized using a “model”, called the chemical mass balance (CMB). The method has been applied periodically since 1968, with major attempts reported in 1975 and 1994, based on large field studies. Despite improvements in particulate sampling and chemical characterization, data availability and major emissions changes, the CMB results qualitatively remain similar. Only broad source categories are identifiable, but they generally make up more than 75% of the total mass concentration. These include primary motor vehicle emissions, suspended (earth) crustal material, and secondary species of ammonium nitrate...

Development of a physical haze and microroughness standard

Abstract: Microroughness, or haze, on wafer surfaces can mask the detection of particles by scanning surface inspection systems (SSIS). The ability of silicon dioxide or other films to function efficiently as insulators depends partially on the underlying microroughness of the silicon surface. For thin oxides, breakdown voltages are reduced commensurately with increased levels of microroughness. There are similar effects on film layers deposited in later processing steps, and an effect on bonding for silicon-on- insulator applications. The disk drive industry depends on a steady transfer rate of data from the recording medium. Imparted surface texture must be carefully controlled since it is in conflict with the desire to have the head in close proximity to the recording surface; however, too fine of a polish can lead to stick-slip or blocking. Additionally, the surface texture must be very uniform across the face of the recording media. The flat panel display industry, with their ubiquitous screens now so common in laptop computers, relies on an orientation layer with a precise amount of microroughness on the substrates. In these and numerous other applications, a well characterized surface is paramount to high production yields. And yet, the most often used of these measurements, rms microroughness, is grossly misunderstood. Surface roughness is not a unique number nor is it an intrinsic surface property. Roughness measurements depend on the parameters of the instrument used for measurement--whether that be an optical or mechanical profiler, a SSIS used for haze detection, or an atomic force microscope. Each of these instruments may give very different values from exactly the same surface. A novel approach to developing a practical haze standard has been employed by photolithographically etching features to as little as 1 nm deep into the surface of 150 mm silicon wafers. To prevent a wafer scanner from detecting these features as particles or other light scattering events, a high surface density (4 X 106 features/cm2) is produced such that the distance between features is much less than the spatial resolution of current instruments (typically 50 micrometers - 100 micrometers ). Once the wafers have been fabricated, the haze or microroughness level detected by a given scanning instrument may then be calculated from the Power Spectral Density function plots generated for each wafer by various techniques (such as angle resolved light scattering or atomic force microscopy). The amount of simulated haze produced by this method is a function of the depth of etch into the silicon surface.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Corneal haze after photorefractive keratectomy. A review of etiological mechanisms and treatment options

Abstract: Purpose. The aim of this paper was to review the literature describing haze subsequent to photorefractive keratectomy (PRK). In particular, it addresses three main areas. Firstly, the time course of cellular and extracellular activity in the generation of haze and variations with species. Secondly, to identify of the omissions in the current database and, thirdly, to indicate of those aspects of the etiology of haze that may have implications for its control or treatment. Methods. Articles concerning haze were identified from a number of databases and information was collated in a systematic fashion. Results. Tables were composed identifying risk factors in clinical and laboratory studies, together with underlying cellular and extracellular changes. Early loss of corneal transparency was predominantly related to changes in numbers, size and density of keratocytes, while late stage changes were shown to be residual keratocyte problems, together with subepithelial deposition of glycosaminoglycans and unstructured collagen. Conclusions. The literature survey showed that, to date, pharmacological manipulation of haze has, for the most part, been unsuccessful. The major contribution to reduction in haze has been the trend towards larger beam sizes. Manufacturers who have adopted 6.00-mm beams, have universally demonstrated a reduction in the number of patients with significant haze.

Quantitative measurement of corneal haze after myopic PRK

Abstract: Objective To design and evaluate an instrument for the objective measurement of haze in rabbits after myopic PRK. Methods A circular fluorescent lamp bulb projected light onto the cornea through a circular collimating aperture covered with an orange filter. The image was collected on a centrally mounted CCD camera and the profile of the haze circle along its horizontal diameter determined. Results Haze circles were observed and quantitated. In the first weeks, they were donut-shaped, frequently with a central bright area, but later they became square-topped. The instrument reproduced measurements with an error of a few percentage points and showed good long-term stability.

Haze Development in Aerobically or Anaerobically Produced Clarified Apple Juices

Abstract: Haze production in aerobically or anaerobically produced Red Delicious apple juice was assessed following heating, aeration, and protein addition. Stored aerobic juice produced haze in 6 wk, but anaerobic juice was haze-free unless oxygen was introduced. Phenolic material was incorporated into haze in both systems. HPLC (detection at 420 nm) of concentrated juice and addition of 100 mg/L BSA suggested the presence in both juices of ‘reactive’ material which could complex and precipitate during storage. Phenolic compounds, heating, and especially oxidation during processing (and storage) appear to be major determinants of ‘haze potential’ in clarified apple juice.

Haze and transmissivity measurements

Abstract: A portable and potentially computer-controlled aircraft windscreen or the like test arrangement for quantitative determination of haze and energy transmissivity characteristics in the windscreen material. The test arrangement includes two portable transducer enclosures which lend to convenient use in tested aircraft environments and provides optical assistance in achieving a desired alignment of these transducer enclosures prior to testing. Improved sensitivity over prior haze evaluation arrangements is achieved through use of this accurate alignment and through capture of a large fraction of a haze generated optical signal with an efficient transducer configuration. The testing arrangement also includes optical filtering capability and laser signal modulation assistance in excluding ambient illumination interference with measurement-related optical signals. A plurality of use environments are contemplated including military and non-military uses.

patterns of dust transport to the Grand Canyon

Abstract: Dust particles in the 2.5 µm to 15 µm diameter range contribute to regional haze that sometimes impairs visibility at the Grand Canyon and other National Parks in the southwestern U.S. The proportion of airborne dust that is attributable to land modification is unknown, but can be expected to increase as a consequence of the region's rapid population growth. This note examines the upwind histories of air masses bringing high coarse-particle concentrations to the Grand Canyon over a five-year monitoring period. Although arid and semi-arid lands extend in all directions, and the fastest airflows generally have a northerly component, high dust concentrations are most common in air arriving from the southwest, where development has been concentrated. This empirical association suggests that the expansion of suburban and agricultural lands is raising dust levels at the Grand Canyon.

Nonlinear mean-square estimation with applications in remote sensing

Abstract: An approach to image modeling based on nonlinear mean-square estimation that does not assume a functional form for the model is described. The relationship between input and output images is represented in the form of a lookup table that can be efficiently computed from, and applied to images. Three applications are presented to illustrate the utility of the technique in remote sensing. The first illustrates how the method can be used to estimate the values of physical parameters from imagery. Specifically we estimate the topographic component (i.e., the variation in brightness caused by the shape of the surface) from multispectral imagery. The second application is a nonlinear change detection algorithm which predicts one image as a nonlinear function of another. In cases where the frequency of change is large (e.g., due to atmospheric and environmental differences), the algorithm is shown to be superior in performance to linear change detection. In the last application, a technique for removing wavelength- dependent space-varying haze from multispectral imagery is presented. The technique uses the IR bands, which are not affected significantly by haze, to predict the visible bands. Results show a significant reduction in haze over the area considered. Additional application areas are also discussed.

Estimation of aerosol microphysical parameters from visible and infrared extinction measurements

Abstract: We show that an effective scattering radius r s and aerosol extinction coefficient at a wavelength of 3.8 micrometer (alpha) e (3.8 micrometer) can be estimated from the simultaneous measurement of visible and 10.6 micrometer extinction in haze and fog. For fog, functions relating r s and (alpha) e (3.8 micrometer) to the ratio of 10.6 micrometer to 0.55 micrometer extinction were derived based on accepted size distribution models for clouds and fog. For haze, functions for r s and (alpha) e (3.8 micrometer) were based on an analysis of measured aerosol size distributions. We compare values of r s and (alpha) e (3.8 micrometer) derived from measurements of local visible and 10.6 micrometer aerosol extinction to values obtained from aerosol size spectra. We conclude that measurements of visible and 10.6 micrometer aerosol extinction provide useful additional information about the aerosol.

Polyester film for transparent gas-barrier film

Abstract: PURPOSE: To obtain a polyester film which has excellent adhesion to a thin transparent vapor-deposited oxide film and is useful for producing a transparent gas-barrier film by regulating the surface roughness, surface haze, and total haze of the film to specific values. CONSTITUTION: This polyester film has a surface roughness (Ra) of 0.02-0.04μm, a surface haze of 1.5% or lower, and a total haze at a thickness of 12μm of 4.0% or lower. An oxide such as SiO2 or Al2 O3 is vapor-deposited as a thin transparent film on the polyester film to produce a transparent gas-barrier film, which is significantly reduced in permeability to gases such as oxygen and water vapor. By adjusting the surface roughness and the surface haze to such values, the polyester film has improved adhesion to the vapor-deposited film, and the gas-barrier film hence withstands, in particular, retorting.