Showing papers on "Haze published in 1993"

Dust emission and transport in Mali, West Africa

Abstract: Vertical dust fluxes were measured in the Inland Delta region of the Niger River, Mali, West Africa, during April-June, 1989 and 1990. Measurements of dust flux represent, for the most part, non-dust storm conditions or ‘dust haze’ periods. The observed concentration versus height relationships are similar to data presented by other investigators. The relationship between wind shear velocity (u*, m s−1) and vertical dust flux (F, μg m−2 s−1) can be described by a relationship in which F is proportional to u*4. However, there is considerable scatter within the data set which is attributable to textural controls and surface conditions. The vertical dust fluxes measured in Mali are compared to dust fluxes measured in Texas, USA, and Yukon Territories, Canada. The significantly different values for the constant of proportionality (a) in the F α a u*4 relationship for these geographically diverse areas is a function of surficial controls on the release of sediments to the air stream. Dust concentrations measured in Mali were found to be uniformly high and in general exceed WHO health standards for acceptable total suspended particulate loadings. As a result background dust may be considered a long term stress on health for the people of this region of Mali.

The occultation of 28 Sgr by Titan

Abstract: We present a comprehensive analysis of data obtained during the 1989 July 3 occultation of 28 Sgr by Titan. The data set includes 23 lightcurves from 15 separate stations, spanning wavelengths from 0.36 to 0.89 micron. A detailed model of the structure of Titan's atmosphere in the altitude range 250 to 450 km is developed, giving the distribution of temperature, pressure, haze optical depth, and zonal wind velocity as a function of altitude and latitude. Haze layers detected in Titan's stratosphere are about one scale height higher than inferred from Voyager data, and show a wavelength dependence indicative of particle sizes on the order of 0.1 micron. A marked north-south dichotomy in haze density is observed with a transition to lower density south of about -20 deg latitude. Zonal wind speeds are inferred from global distortions from spherical symmetry and are of the order of 100 m/s with significant increase toward higher latitudes. Titan's high atmosphere shows substantial axial symmetry; the position angle of the symmetry axis is equal to the position angle of Saturn's spin axis to within about 1 deg.

Recent changes in the North American Arctic boundary layer in winter

Abstract: Analysis of significant level radiosonde data from a network of Arctic stations reveals a systematic reduction in midwinter surface-based inversion depths over the past few decades, accompanied by a rise in surface temperature. Similar trends are observed over a wide sector, from 62°W to 162°W and from 70°N to 83°N. Possible causes for these changes include increases in warm air advection, cloud cover, ice crystals, aerosols, and greenhouse gases, but the specific reasons are difficult to identify, due to strong interactions between many potentially important factors. Nevertheless, the changes are significant for studies of Arctic haze, since the midwinter stable boundary layer has been decreasing in depth over time.

A long‐term decrease in Arctic haze at Barrow, Alaska

Abstract: Surface aerosol scattering measurements have been conducted at Barrow, Alaska, from May 1976 to the present using a four-wavelength nephelometer. Total column aerosol optical depth measurements have been obtained over the same time period. Both data sets show a maximum in 1982 and then a decreasing trend to the present. This decreasing trend is apparent, and statistically significant, only in March–April. Arctic haze, caused by long-range transport from midlatitude industrial regions, is most evident in the vicinity of Barrow during this time of year. We suggest that the decrease in Arctic haze at Barrow, as observed in the aerosol light scattering and optical depth records, is due to decreased anthropogenic pollution emissions in Europe and the former Soviet Union, the primary source regions for the springtime aerosol at Barrow. Volcanic effects in the stratosphere have been subtracted from the optical depth data, and are not believed to be significant in the surface-based data.

Empirical Studies of Tropospheric Transmission in the Ultraviolet: Broadband Measurements

Abstract: This work examines the effects of absorption and scattering in the troposphere on solar ultraviolet radiation reaching the ground. A site was established in the city of Chicago for monitoring broadband ultraviolet irradiance, total sunlight, and the ground-level mixing ratios of ozone and nitrogen dioxide. The radiation sensors were a Robertson-Berger meter and an Eppley pyranometer. Interpretation of the measurements leads to the following conclusions. During the time period studied, the attenuation provided by clouds and haze underwent an annual cycle. The monthly mean ultraviolet irradiance measured by the Robertson-Berger meter ranged from 84.0% of the clear-sky value for June 1991 to 49.1% for January 1992. Average ultraviolet irradiances for June and July of 1992 were 10.6% and 21.7% lower than in corresponding months of 1991, owing to differences in local cloudiness. The attenuation of total sunlight provided by local clouds and haze was the same as their attenuation of ultraviolet radiati...

Haze and sulfur emission trends in the eastern United States

Abstract: The paper presents the regional and seasonal trends of haziness in the Eastern U.S. from 1948 to 1982. Haze or haziness, measured quantitatively at the extinction coefficient, is derived via the Koschmeider relationship from human observer visibility observations made at airport stations of the National Weather Service. The trend analysis shows significant changes in haziness, particularly in the southeastern part of the U.S. The haze trends are compared to the emission trends of sulfur dioxide. These two parameters exhibit similar regional and seasonal trends.

Arctic haze: Perturbation to the radiation field

Abstract: A model of the polluted arctic troposphere is constructed to estimate the magnitude and seasonal variation of the climate forcing function of arctic haze. Using a pill-box “bathtub model” for the Arctic and envisioning it to be filled with pollution from industrial sources in Eurasia, we estimate that maximum climate perturbation from arctic contamination occurs in the spring months. The major perturbation to the radiation budget is a lowering of the albedo (heating) of the earth-atmosphere system around the vernal equinox and is due to a trace amount (about 5% by mass) of black carbon associated with the removal-resistant submicron mode of aerosols. The black carbon over the reflecting polar ice/snow introduces a heating of about 1.5 degree per day into the haze layer.

Dust in the Martian atmosphere: Polarimetric sensing

Abstract: Telescopic optical polarimetry over the planet Mars enables us to detect and localize scatterers in the Martian atmosphere Polarization discriminates between crystal clouds and dust particles For dust grains, sizes can be derived There is an increase in size from very small grains forming the permanent dust haze to sub-micrometer size grains for the local dust veils and the several micrometer size pieces found in the dust storm clouds From all these polarimetric results, an overview emerges about the behavior of dust particles in the Martian atmosphere

Course of subepithelial corneal haze over 18 months after photorefractive keratectomy for myopia [corrected].

Abstract: This study of 285 myopic eyes treated with photorefractive keratectomy (PRK), with a maximum follow up of 18 months, was designed to analyze the clinical subepithelial significance of corneal haze after excimer laser PRK. The treatment parameters included an ablation zone diameter from 3.6 to 5 mm, ablation rate from 0.22 to 0.25 micron pulse, fluence of 180 mJ/cm2, and frequency of 10 Hz. All patients used a standard topical corticosteroid regimen. A statistical analysis of the subjective haze grading showed a maximum at 3 months (mean grading, 1.03) and a decrease to 0.38 at 18 months. Haze is statistically greater with higher amounts of treatment (p = .003 between 2.00 D and 3.00 D groups, p = .0002 between 2.00 D and 6.00 D groups). In males (p = .0004), and in ablations less than 4.5 mm diameter (p = .0002) but no difference was found related to age. The overall frequency of clinically significant haze was 11.5% with a mean age of 35.1 years and a mean attempted correction of -5.71 D. This frequency increased to 24% in the 6.20 D to 9.90 D group and 38.6% in the 4.4 mm and less group, and it decreased to 8.6% in the 1.00 D to 6.00 D group and 6.6% in the 4.5 and 5 mm group. All patients with significant haze gave a history of discontinued use of corticosteroids. We suggest there exists a significant haze risk group in which the absence of steroid or discontinuation of corticosteroids will lead to significant haze.

The detectability of Arctic leads using thermal imagery under varying atmospheric conditions

Abstract: The way in which thermal contrast between leads of varying widths and thickness can be distinguished from the background multiyear ice surface under varying atmospheric conditions is examined. The normalized brightness temperature difference between image pixels that include lead fractions and of the background ice is employed to determine thresholds of detection accounting for sensor FOV and various atmospheric phenomena that influence the Arctic radiation balance during winter. Surface temperatures are prescribed as a function of ice thickness, and the effects of the intervening atmosphere are simulated by varying the optical depths of hypothetic cloud or haze layers varying in microphysical characteristics. It is found that the limits of lead detection may be determined as a function of pixel lead fraction and atmospheric optical depth if suitable values of normalized contrast are used as detection criteria.

On the haze model for Triton

Abstract: Some improvements are introduced into the haze model by Krasnopolsky et al. (1992), which describes growth and precipitation of particles formed by methane photolysis. These improvements take into account a possible termination of the Voyager Ultraviolet Spectrometer (UVS) occultation observations by clouds and a more accurate presentation of the surface reflection by a modified Hapke function. All changes are within the uncertainties of the previous model, though not negligible. The particle mean radius and number density for global mean conditions vary from 0.1±0.01 μm and 2.4 cm−3 at 30 km to 0.135±0.015 pm and 10.4 cm−3 near the surface. The scale height of the volume extinction coefficient in the visible varies from 7 km at h=25 km to 15 km at h=5 km. The vertical optical thickness of haze is equal to (5±1) × 10−3 at 0.47 μm.

Optical properties of continental haze and cumulus and orographic clouds based on Space Shuttle polarimetric observations

Abstract: Digitized Space Shuttle imagery in the red, green, and blue spectral regions (0.600, 0.540, and 0.435 µm, respectively) is used to characterize the mean radius and the index of refraction of droplets in cumulus and orographic clouds. The clouds are shown to consist concurrently of submicrometer and supermicrometer droplets, with the percent polarization indicative of the dominant sizes. Cloud development from haze as well as inhomogeneities in the cloud decks can be traced remotely. The absorption properties of clouds can also be determined remotely. An optical depth of continental haze in the same three spectral regions as the clouds is computed from the polarimetric and photometric contributions. Both Mie and Rayleigh scattering are included in the model.

Control of time-dependent haze in the manufacture of integrated circuits

Abstract: The onset of haze on silicon wafers is controlled by treating the wafers with a chemical selected from the group consisting of hot water and isopropyl alcohol and then storing the treated wafers in an inert atmosphere such as nitrogen or argon.

System for three-dimensional map display of foreign matter on wafer

Abstract: PURPOSE:To execute three-dimensional map display which allows a haze density distribution and its gradient state to be observed by a short-time processing and fine particles discriminated by extracting signal components to fine particles and haze from received signals and by preparing a display element with a height proportional to an intensity of received signals at the bottom of a length of a unit cell. CONSTITUTION:Upon entry of a received signal of a photomultiplier tube (PMT) 32 into a fine particle detector 4 and a haze detector 5, a signal of detected fine particles p is outputted by a fine particle detector 42, and a signal of detected haze H by a haze detector 52. Further, the signal is sampled/digitized by timing signal St corresponding to a wafer unit cell, so that a display element is prepared by a three-dimensional display processor 8 and displayed by three- dimensional map on a displayer 7. Hereupon, the bottom width DELTAx of a bar-type display element is the same as the length of a unit cell, and height. DELTAy is made proportional to the magnitude of each sampled signal. This process can apply a display element for wafer inspection of flow work.

Arctic haze: Patterns and relationships to regional signatures of trace gases

Abstract: We took measurements of up to 30 gases in Arctic haze and in clean Arctic air. These data were obtained from some 500 flask samples taken on three expeditions of the Arctic Gas and Aerosol Sampling Program (AGASP 1, 2, and 3) during the spring of 1983, 1986, and 1989. Concentrations of many gases are significantly higher in the haze layers compared to outside the haze. To look for the possible origins of the haze, we used cluster analysis to derive regional signatures of trace gases at ground-based sites in middle and high northern latitudes. Comparison of the regional signatures with concentrations observed in Arctic haze suggest that there are no significant contributions from North America but possible influences from Russia and eastern Europe. These conclusions complement results derived from the analysis of the Arctic aerosol chemistry. It is possible, however, that Arctic haze originates from the military, industrial, and mining activities within the Arctic circle, particularly from the Russian Koala peninsula.