Showing papers on "Haze published in 2003"
TL;DR: An approach for easily removing the effects of haze from passively acquired images based on the fact that usually the natural illuminating light scattered by atmospheric particles (airlight) is partially polarized, which yields a range map of the scene which enables scene rendering as if imaged from different viewpoints.
Abstract: We present an approach for easily removing the effects of haze from passively acquired images. Our approach is based on the fact that usually the natural illuminating light scattered by atmospheric particles (airlight) is partially polarized. Optical filtering alone cannot remove the haze effects, except in restricted situations. Our method, however, stems from physics-based analysis that works under a wide range of atmospheric and viewing conditions, even if the polarization is low. The approach does not rely on specific scattering models such as Rayleigh scattering and does not rely on the knowledge of illumination directions. It can be used with as few as two images taken through a polarizer at different orientations. As a byproduct, the method yields a range map of the scene, which enables scene rendering as if imaged from different viewpoints. It also yields information about the atmospheric particles. We present experimental results of complete dehazing of outdoor scenes, in far-from-ideal conditions for polarization filtering. We obtain a great improvement of scene contrast and correction of color.
519 citations
TL;DR: In this article, individual aerosol particles in smoke plumes from biomass fires and in regional hazes in southern Africa were studied using analytical transmission electron microscopy (TEM), which allowed detailed characterization of carbonaceous particle types in smoke and determination of changes in particle properties and concentrations during smoke aging.
Abstract: [1] Individual aerosol particles in smoke plumes from biomass fires and in regional hazes in southern Africa were studied using analytical transmission electron microscopy (TEM), which allowed detailed characterization of carbonaceous particle types in smoke and determination of changes in particle properties and concentrations during smoke aging. Based on composition, morphology, and microstructure, three distinct types of carbonaceous particles were present in the smoke: organic particles with inorganic (K-salt) inclusions, ‘‘tar ball’’ particles, and soot. The relative number concentrations of organic particles were largest in young smoke, whereas tar balls were dominant in a slightly aged (1 hour) smoke from a smoldering fire. Flaming fires emitted relatively more soot particles than smoldering fires, but soot was a minor constituent of all studied plumes. Further aging caused the accumulation of sulfate on organic and soot particles, as indicated by the large number of internally mixed organic/sulfate and soot/sulfate particles in the regional haze. Externally mixed ammonium sulfate particles dominated in the boundary layer hazes, whereas organic/sulfate particles were the most abundant type in the upper hazes. Apparently, elevated haze layers were more strongly affected by biomass smoke than those within the boundary layer. Based on size distributions and the observed patterns of internal mixing, we hypothesize that organic and soot particles are the cloudnucleating constituents of biomass smoke aerosols. Sea-salt particles dominated in the samples taken in stratus clouds over the Atlantic Ocean, off the coast of Namibia, whereas a distinct haze layer above the clouds consisted of aged biomass smoke particles. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions; 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry; KEYWORDS: biomass burning, carbonaceous aerosol, individual particles, TEM
408 citations
Journal Article•
TL;DR: In this paper, individual aerosol particles in smoke plumes from biomass fires and in regional hazes in southern Africa were studied using analytical transmission electron microscopy (TEM), which allowed detailed characterization of carbonaceous particle types in smoke and determination of changes in particle properties and concentrations during smoke aging.
Abstract: Individual aerosol particles in smoke plumes from biomass fires and in regional hazes in southern Africa were studied using analytical transmission electron microscopy (TEM), which allowed detailed characterization of carbonaceous particle types in smoke and determination of changes in particle properties and concentrations during smoke aging. Based on composition, morphology, and microstructure, three distinct types of carbonaceous particles were present in the smoke: organic particles with inorganic (K-salt) inclusions, tar ball particles, and soot. The relative number concentrations of organic particles were largest in young smoke, whereas tar balls were dominant in a slightly aged (1 hour) smoke from a smoldering fire. Flaming fires emitted relatively more soot particles than smoldering fires, but soot was a minor constituent of all studied plumes. Further aging caused the accumulation of sulfate on organic and soot particles, as indicated by the large number of internally mixed organic/sulfate and soot/sulfate particles in the regional haze. Externally mixed ammonium sulfate particles dominated in the boundary layer hazes, whereas organic/sulfate particles were the most abundant type in the upper hazes. Apparently, elevated haze layers were more strongly affected by biomass smoke than those within the boundary layer. Based on size distributions and the observed patterns of internal mixing, we hypothesize that organic and soot particles are the cloud-nucleating constituents of biomass smoke aerosols. Sea-salt particles dominated in the samples taken in stratus clouds over the Atlantic Ocean, off the coast of Namibia, whereas a distinct haze layer above the clouds consisted of aged biomass smoke particles.
401 citations
TL;DR: In this article, the authors presented a method to detect the presence of a single particle in the UHRA data set of the Earth's magnetic field using a single-dimensional model.
Abstract: Original article can be found at: http://www.agu.org/journals/jd/ Copyright American Geophysical Union DOI: 10.1029/2002JD002226 [Full text of this article is not available in the UHRA]
262 citations
TL;DR: Using a one-dimensional photochemical model, an investigation into the chemical mechanisms responsible for the formation of Titan's haze region is conducted in this article, which demonstrates that the growth of polycyclic aromatic hydrocarbons throughout the lower stratosphere plays an important role in furnishing the main haze layer with nitriles playing a secondary role.
189 citations
TL;DR: This article showed that the change in black carbon morphology, from a chain to a clump-like structure, does not significantly affect the bulk aerosol single scattering albedo, and that scattering material from the gas phase appears to be the dominant mechanism.
Abstract: [1] Measurements on the UK Met Office C-130 within a distinct biomass burning plume during the Southern AFricAn Regional science Initiative (SAFARI 2000) show an increase in the single scattering albedo as the aerosol ages, from 0.84 at source to 0.90 in the aged regional haze in 5 hours. Condensation of scattering material from the gas phase appears to be the dominant mechanism; the change in black carbon morphology, from a chain to clump like structure, does not significantly affect the bulk aerosol single scattering albedo.
173 citations
TL;DR: In this article, the authors collected filter samples of the atmospheric aerosol during the Southern African Regional Science Initiative (SAFARI 2000) experiment onboard the UK Met Office C-130 aircraft.
Abstract: [1] We collected filter samples of the atmospheric aerosol during the Southern African Regional Science Initiative (SAFARI 2000) experiment onboard the UK Met Office C-130 aircraft. The main operational area was the Atlantic Ocean offshore of Namibia and Angola, where biomass-smoke haze at least 1–2 days old was widespread. The size-fractionated aerosol samples were analyzed for the major inorganic ions, carbonaceous material (elemental and organic carbon), and elements with atomic numbers between 11 (Na) and 82 (Pb). The regional haze aerosol was composed mostly of carbonaceous aerosols (on the average, 81% of the submicron mass), with secondary inorganic aerosols (sulfate, ammonium, and nitrate) accounting for another 14%. K+ and Cl−, typical pyrogenic species, constituted only 2% of the mass. The aerosol chemical data were used to estimate mass emission fluxes for various aerosol components. For African savanna/grassland burning, the estimated emission flux of carbonaceous particles (particulate organic matter plus elemental carbon) is 14 ± 1 Tg yr−1, and that of the nitrogen species (nitrate and ammonium) is 2 ± 2 Tg yr−1. For the flight segments in regional haze, the mean particle scattering coefficient at 550 nm was σs = 101 ± 56 Mm−1 and the mean particle absorption coefficient σa at 565 nm averaged 8 ± 5 Mm−1 (mean single scattering albedo of 0.93 ± 0.06 at 550 nm). The dry mass scattering efficiency αs, calculated from the linear regression of the mean scattering versus the estimated submicron mass, is estimated to be between 4.2 ± and 4.6 ± 0.6 m2 g−1, depending on the assumptions made in calculating the aerosol mass. The dependence of the scattering enhancement ratios Δσs/ΔCO on the distance from the burning regions suggests that the evolution of particle size with time influences the light scattering efficiency. Fresh smoke was sampled during a dedicated flight in the proximity and within the plume of an active biomass burning fire. Here the enhancement ratio with respect to CO of particles in the Aitken-size range (5–100 nm diameter) was ΔNAitken/ΔCO ∼25 cm−3 (STP) ppb−1. These particles were removed rapidly after emission, and they were not detectable in the regional haze. The enhancement ratio for accumulation mode particles (0.1–1 μm diameter) ΔNAcc/ΔCO was ∼26–30 cm−3 (STP) ppb−1 in young smoke, and 16 ± 3 cm−3 (STP) ppb−1 in aged haze, suggesting that the number concentration of accumulation mode particles was reduced by about 41% during aging.
172 citations
TL;DR: In this article, the authors measured the net solar spectral irradiance at flight levels throughout biomass burning haze layers and derived the flux divergence, fractional absorption, instantaneous heating rate, and absorption efficiency.
Abstract: During the dry season component of the Southern African Regional Science Initiative (SAFARI) in late winter 2000, the net solar spectral irradiance was measured at flight levels throughout biomass burning haze layers. From these measurements, the flux divergence, fractional absorption, instantaneous heating rate, and absorption efficiency were derived. Two cases are examined: on 24 August 2000 off the coast of Mozambique in the vicinity of Inhaca Island and on 6 September 2000 in a very thick continental haze layer over Mongu, Zambia. The measured absolute absorption was substantially higher for the case over Mongu where the measured midvisible optical depth exceeded unity. Instantaneous heating from aerosol absorption was 4 K d(sup -1) over Mongu, Zambia and 1.5 K d(sup -1) near Inhaca Island, Mozambique. However, the spectral absorption efficiency was nearly identical for both cases. Although the observations over Inhaca Island preceded the river of smoke from the southern African continent by nearly 2 weeks, the evidence here suggests a continental influence in the lower tropospheric aerosol far from source regions of burning.
130 citations
TL;DR: In this article, a unique aerosol Raman lidar at Hulhule (4� N, 73� E), Maldives, was used to determine the volume extinction coefficient of the particles at 355 and 532 nm at ambient conditions.
Abstract: [1] Multiwavelength backscatter and extinction profiling was performed with a unique aerosol Raman lidar at Hulhule (4� N, 73� E), Maldives, as part of the Indian Ocean Experiment (INDOEX) between February 1999 and March 2000. The Raman lidar allowed a direct determination of the volume extinction coefficient of the particles at 355 and 532 nm at ambient conditions. Heavily polluted air masses from the Asian continent passed over the Maldives during the northeast monsoon seasons. The mean 532-nm particle optical depth was about 0.3; maximum values of 0.7 were measured. Above the polluted marine boundary layer, lofted plumes were found up to 4000-m height. On average, the freetropospheric aerosol layers contributed 30–60% to the particle optical depth. The volume extinction coefficient at 532 nm typically ranged from 25 to 175 Mm � 1 in the elevated layers. The pollution plumes are characterized separately for the air masses from Southeast Asia, North India, and South India. The analysis includes backward trajectories and emission inventory data for India. The extinction-to-backscatter ratio (lidar ratio) at 532 nm was mostly between 30 and 100 sr, and accumulated at 50–80 sr for highly absorbing particles from northern India. The shift of the lidar-ratio distribution for northern Indian aerosols by about 20 sr toward larger values compared to European values is consistent
130 citations
TL;DR: Comparisons of data with the Interagency Monitoring of Protected Visual Environments network suggest that SO4 2− is more regional than carbonaceous material and originates in part from upwind source regions, and the light extinction coefficient is well correlated to PM2.5.
Abstract: Observations of the mass and chemical composition of particles less than 2.5 m in aerodynamic diameter (PM2.5), light extinction, and meteorology in the urban Baltimore-Washington corridor during July 1999 and July 2000 are presented and analyzed to study summertime haze formation in the mid-Atlantic region. The mass fraction of ammoniated sulfate (SO4 2 ) and carbonaceous material in PM2.5 were each 50% for cleaner air (PM2.5 10 g/m 3 ) but changed to 60% and 20%, respectively, for more polluted air (PM2.5 30 g/m 3 ). This signifies the role of SO4 2 in haze formation. Comparisons of data from this study with the Interagency Monitoring of Protected Visual Environments network suggest that SO4 2 is more regional than carbonaceous material and originates in part from upwind source regions. The light extinction coefficient is well correlated to PM2.5 mass plus water associated with inorganic salt, leading to a mass extinction efficiency of 7.6 1.7 m 2 /g for hydrated aerosol. The most serious haze episode occurring between July 15 and
88 citations
TL;DR: The current state of knowledge regarding the chemistry of forest fires and regional haze is reviewed in this article, where more than 100 compounds have been identified in wood smoke and many of these have also been observed in field studies.
Abstract: The current state of knowledge regarding the chemistry of forest fires and regional haze is reviewed. More than 100 compounds have been identified in wood smoke and many of these have also been observed in field studies. Products of biomass combustion can have different environmental effects: CO2and CH4may contribute to global warming, NOx and SO2could contribute to rainwater acidity, whereas smoke particles and polynuclear aromatic hydrocarbons (PAHs) could affect human health. Also, photochemical reactions of primary emissions from biomass fires can lead to the production of secondary pollutants such as 03. Regional haze episodes caused by forest fires have occurred in SE Asia on several occasions during the 1990s and the reported studies of these episodes are reviewed. Only total suspended particles (TSP) were determined in the earlier studies, and more comprehensive chemical investigations have only emerged during the more recent episodes, notably those of 1997 and 1998. To date, most of the measurements have centred on criteria pollutants (SO2, NO2, CO, O3 and PM10), however, other pollutants (e.g., VOCs, PAHs) have also been determined in certain studies. Rainwater analyses suggest that forest fires do not have a major acidifying effect because dissolved acidic gases (e.g., SO2) are neutralised by alkaline substances (e.g., Ca, Mg, K) that are also emitted by forest fires. There is a need for further laboratory and field studies in order to investigate important pollutant transformation mechanisms.
Journal Article•
TL;DR: In this article, the authors used the mist chamber/ion chromatography technique to quantify fine aerosol sulfate in the Arctic during the Tropospheric Ozone Production about the Spring Equinox Experiment (TOPSE) with about 2.5 min time resolution.
Abstract: We used the mist chamber/ion chromatography technique to quantify fine aerosol SO = 4 (<2.7 μm) in the Arctic during the Tropospheric Ozone Production about the Spring Equinox Experiment (TOPSE) with about 2.5 min time resolution. Our effective sample area ranged from 50° to 86°N and 53° to 100°W. The seasonal evolution of fine aerosol sulfate in the Arctic troposphere during TOPSE was consistent with the phenomenon of Arctic haze. Arctic haze has been attributed to pollution from sources in the Arctic and pollution transported meridionally along stable isentropes into the Arctic in geographically broad but vertically narrow bands. These layers became more prevalent at higher altitudes as the season progressed toward summer, and the relevant isentropes are not held so close to the surface. Mean fine particle SO 4 = mixing ratios during TOPSE in February below 1000 m were elevated (112 pptv) and highly variable (between 28 and 290 pptv) but were significantly lower at higher altitudes (about 40 pptv). As the season progressed, elevated mixing ratios and higher variability were observed at higher altitudes, up to 7 km. In May, mixing ratios at the lowest altitudes declined but still remained higher than in February at all altitudes. The high variability in our measurements likely reflects the vertical heterogeneity of the wintertime Arctic atmosphere as the airborne sampling platform passed in and out of these layers. It is presumed that mixing ratios and variability will continue to decline at all altitudes into the summer as wet deposition processes become important in removing aerosol SO = 4 from the troposphere.
TL;DR: In this article, the authors used the geometric albedo and several results and constraints from other works to better constrain the vertical haze extinction profile, especially in the low stratosphere.
TL;DR: The results indicate that PM10 and CO levels during the haze period have a significant bearing on the incidence of respiratory diseases (Asthma, Acute Respiratory Infections and Influenza (ARII)).
Abstract: Air pollution episodes as a result of forest fires in Brunei Darussalam and neighbouring regions have reached hazardous levels in recent years Such episodes are generally associated with poor visibility and air quality conditions In the present study, data on PM10(particulate matter of size less than 10 microns) and CO in Brunei Darussalam have been considered to study the incidence of respiratory diseases whereas data on relative humidity (RH) in addition to PM10 have been used to explain the visibility with a particular emphasis on haze episode during 1998
TL;DR: In this article, the authors demonstrate that the U.S. pollution plume can be as intense (in terms of aerosol mass concentration, aerosol optical depth, and ozone mixing ratio) as those downwind of India and Asia affecting regional climate along the United States East Coast.
Abstract: [1] Pollution plumes recur seasonally downwind of the Indian subcontinent and Asian continent due to industrial and vehicular emissions, biomass burning, and wind-blown dust. These plumes have been well documented by field campaigns and satellite observations and the environmental implications of the “Asian Brown Cloud” have been widely publicized in a recently released UNEP report [UNEP and C4, 2002]. Recent field experiments, however, demonstrate that the U.S. pollution plume can be as intense (in terms of aerosol mass concentration, aerosol optical depth, and ozone mixing ratio) as those downwind of India and Asia affecting regional climate along the U.S. East Coast. The use of identical sampling protocols in these experiments has been key in eliminating sampling biases and making the data directly comparable.
TL;DR: In this paper, the evidence for smoke being a significant contributor to aerosol during periods of excessive haze is discussed and includes features of the aerosol chemistry, the diurnal cycle of Bsp, and the coincidence of forest fires on Sumatra during the southwest (SW) monsoon period, as well as transport modelling for one week of the southwest Monsoon of 2000.
Abstract: Continuous measurements of dry aerosol light scattering (Bsp) were made at two sites in the Klang Valley of Malaysia between December 1998 and December 2000. In addition 24-h PM2.5 samples were collected on a one-day-in-six cycle and the chemical composition of the aerosol was determined. Periods of excessive haze were defined as 24-h average Bsp values greater than 150 Mm-1 and these occurred on a number of occasions, between May and September 1999, during May 2000, and between July and September 2000. The evidence for smoke being a significant contributor to aerosol during periods of excessive haze is discussed and includes features of the aerosol chemistry, the diurnal cycle of Bsp, and the coincidence of forest fires on Sumatra during the southwest (SW) monsoon period, as well as transport modelling for one week of the southwest Monsoon of 2000. The study highlights that whilst transboundary smoke is a major contributor to poor visibility in the Klang Valley, smoke from fires on Peninsular Malaysia is also a contributor, and at all times, the domestic source of secondary particle production is present.
TL;DR: In this paper, the estimates of the radiative forcing during the 1997 Indonesia's forest fire have been obtained by integrating satellite derived aerosol optical depths and cloud cover with in-situ observations of single scattering albedo and a Monte-Carlo Aerosol-Cloud radiation model.
Abstract: [1] During the last decade, the feedback between El Nino and biomass burning caused the Indonesia's forest fire aerosols to be the second most significant source of anthropogenic aerosol over the tropical Indian Ocean after the South Asian Haze. In this paper, the estimates of the radiative forcing during the 1997 Indonesia's forest fire have been obtained by integrating satellite derived aerosol optical depths and cloud cover with in-situ observations of single scattering albedo and a Monte-Carlo Aerosol-Cloud radiation model. The haze reduced the seasonal average solar radiation absorbed by the equatorial Indian ocean by as much as 30 to 60 W m−2 during September to November 1997, and increased the atmospheric solar heating by as much as 50% to 100% within the first 3 kilometers. The radiative forcing at the top of the atmosphere (TOA) was in the range of 5 to 15 W m−2 under cloudy skies. The significance of such large radiative flux changes to the tropical ocean-atmosphere heat budget and climate needs to be examined with climate models.
TL;DR: Yamanouchi et al. as mentioned in this paper focused on the mixing states of aerosol constituents and their vertical distribution in spring Arctic troposphere during the ASTAR 2000 campaign and identified sulfate and soot as major aerosols under both Arctic haze and background conditions, and sea-salts are major only in lower troposphere (<3 km above sea level.
Abstract: [1] The present study mainly focuses on the mixing states of aerosol constituents and their vertical distribution in spring Arctic troposphere during the ASTAR 2000 campaign (T. Yamanouchi et al., Arctic Study of Tropospheric Aerosol and Radiation (ASTAR) campaign: An overview and first results, submitted to Bulletin of the American Meteorological Society, 2002) (hereinafter referred to as Yamanouchi et al., submitted manuscript, 2002). Sulfate and soot were identified as major aerosol under both Arctic haze and background conditions, and sea-salts are major only in lower troposphere (<3 km above sea level). Mineral/dusts and unknown species were obtained as minor constituents during the ASTAR 2000 campaign. Airborne aerosol measurements were carried out under the Arctic haze (23 March), and aerosol-enriched (20 March and 12 April) conditions. The highest relative abundance of soot (∼94.7%) was observed in free troposphere on 23 March, when the heaviest Arctic haze condition during the ASTAR 2000 campaign (Yamanouchi et al., submitted manuscript, 2002) was transported directly from Russian industrial regions to the measuring area for several days. Moreover, whereas the external mixing of soot and sulfate dominated under the Arctic haze and aerosol enriched conditions, in the background conditions the internal mixing is dominant. On the other hand, most of aerosol particles containing sulfate had the external mixing states with soot and other aerosol constituents in the free troposphere under both the Arctic haze and background conditions. Sea-salts are dominant only in the lower troposphere (<3 km asl), although a few sea-salt particles were observed in the middle-upper troposphere (3–7 km). Some sea-salt particles were modified (Cl− depleted) in the lower troposphere (<3 km) during the ASTAR 2000 campaign.
TL;DR: In this paper, in situ measurements of vertical profiles of aerosol light scattering, light absorption, and single scattering albedo (omega (sub 0)) are presented for a number of locations in southern Africa during the dry, biomass burning season.
Abstract: Airborne in situ measurements of vertical profiles of aerosol light scattering, light absorption, and single scattering albedo (omega (sub 0)) are presented for a number of locations in southern Africa during the dry, biomass burning season. Features of the profiles include haze layers, clean air slots, and marked decreases in light scattering in passing from the boundary layer into the free troposphere. Frequency distributions of omega (sub 0) reflect the strong influence of smoke from biomass burning. For example, during a period when heavy smoke was advected into the region from the north, the mean value of omega (sub 0) in the boundary layer was 0.81 +/- 0.02 compared to 0.89 +/- 0.03 prior to this intrusion. Comparisons of layer aerosol optical depths derived from the in situ measurements with those measured by a Sun photometer aboard the aircraft show excellent agreement.
TL;DR: In this article, the authors used thermal and optical methods to analyze the total carbon, organic carbon, and black carbon contents of smoke plumes of burning savanna and in regional haze.
Abstract: Particulate matter collected aboard the University of Washington's Convair-580 research aircraft over southern Africa during the dry, biomass burning season was analyzed for total carbon, organic carbon, and black carbon contents using thermal and optical methods. Samples were collected in smoke plumes of burning savanna and in regional haze. A known artifact, produced by the adsorption of organic gases on the quartz filter substrates used to collect the particulate matter samples, comprised a significant portion of the total carbon collected. Consequently, conclusions derived from the data are greatly dependent on whether or not organic carbon concentrations are corrected for this artifact. For example, the estimated aerosol co-albedo (1 - single scattering albedo), which is a measure of aerosol absorption, of the biomass smoke samples is 60 percent larger using corrected organic carbon concentrations. Thus, the corrected data imply that the biomass smoke is 60 percent more absorbing than do the uncorrected data. The black carbon to (corrected) organic carbon mass ratio (BC/OC) of smoke plume samples (0.18/2610.06) is lower than that of samples collected in the regional haze (0.25/2610.08). The difference may be due to mixing of biomass smoke with background air characterized by a higher BC/OC ratio. A simple source apportionment indicates that biomass smoke contributes about three-quarters of the aerosol burden in the regional haze, while other sources (e.g., fossil fuel burning) contribute the remainder.
TL;DR: This retrospective nonrandomized clinical study suggests that oral ascorbic acid supplementation may have a prophylactic effect against haze development after PRK, however, routine proPHylactic use of ascorBate can be recommended only after a randomized, prospective clinical trial substantiates its efficacy.
Abstract: PURPOSE: To evaluate whether prophylactic systemic ascorbic acid influences the average level of haze and the incidence of late onset corneal haze after photorefractive keratectomy (PRK). METHODS: Two consecutive groups of eyes treated with PRK for myopia with or without astigmatism were retrospectively compared. The patients had been treated similarly, with the exception that systemic ascorbate had been supplied orally in one of the groups. Haze intensity was quantified on a scale from 0 (clear cornea) to 4 (anterior chamber not visible). The diagnostic criterion for late onset corneal haze was a haze grade 2 or higher, occurring 4 to 12 months after surgery. RESULTS: One week, 1, 3, 6, and 12 months after surgery, the group without ascorbate (314 eyes) showed haze of average levels 0.61, 0.51, 0.50, 0.32, 0.10, respectively, and the group with ascorbate (201 eyes) showed haze of average levels 0.38, 0.18, 0.16, 0.09, 0.06, respectively. Comparison of the respective values showed a statistically significant difference between the two groups (P<.01) at 1 week, 1, 3, and 6 months. Late onset corneal haze was observed in 11 eyes in the group without ascorbate, and none was observed in the group with ascorbate (P<.02).
TL;DR: In this article, the real ( n) and imaginary (k) parts of the complex refractive index of haze analogs formed from four different gas mixtures were calculated from the spectral properties of the solid polymer in UV-visible, near infrared and infrared wavelength spectral regions.
TL;DR: In this paper, a new scientific payload is introduced for fine-scale measurements of meteorological (wind vector, static air temperature, humidity, and air pressure) and microphysical properties, suspended below a tethered balloon.
Abstract: A new scientific payload is introduced for fine-scale measurements of meteorological (wind vector, static air temperature, humidity, and air pressure) and microphysical (aerosol particles and cloud droplets) properties, suspended below a tethered balloon. The high resolution sensors and the tethered balloon are described. Measurements in a lifted fog layer from a first field campaign are presented.The detailed investigation of the fog/haze and the temperature inversion layer demonstrates the damping influence of the fog on temperature fluctuations, while thewind fluctuations are significantly decreased by theevolving temperature inversion, whichwas about 30 m above the fog layer.From spectral analysis the noise floors of the high-resolution sensors are determined to10-6 kg m-3 for the LWC (liquid water content) and 4 mK for the fast temperature sensor (UFT-B). The correlation betweentemperature and LWC structures in shallow haze layers is investigated. The release of latent heat and the corresponding warming in the haze of about 0.1 K could be quantified.
TL;DR: Radiometric analyses of pseudoinvariant features (dense forest stands) indicate that effective haze reduction can be realized for differential HOT response levels of up to 20 for Landsat Thematic Mapper scenes, and its impact on classification performance is evaluated.
Abstract: A number of haze removal methods for satellite imagery have been described in the literature, but few papers have quantified their effectiveness within the context of a postprocessing applications scenario. The haze optimized transform (HOT) approach for visible-band correction is described, and its impact on classification performance is evaluated. Assessment is conducted at three levels: radiometric level of accuracy, improvement in interclass separability, and classification accuracy. Results obtained from hazy scenes and their dehazed counterparts are compared with those from reference or "benchmark" clear scenes. Radiometric analyses of pseudoinvariant features (dense forest stands) indicate that effective haze reduction can be realized for differential HOT response levels of up to 20 for Landsat Thematic Mapper scenes. This level of atmospheric contamination is severe enough to result in significant thematic class confusion, wherein visible-band radiances of vegetated areas are at levels normally associated with urban features under clear sky conditions.
04 Mar 2003
TL;DR: In this paper, the authors defined the fire-related policy problems as smoke haze pollution, forest degradation and deforestation, and impacts on the rural sector and identified some of the apparent major causes of the problems.
Abstract: Fires are considered a potential threat to sustainable development for their direct impacts on ecosystems, their contribution to carbon emissions, and impacts on biodiversity. In 1997/98, Indonesia had the most severe fires worldwide, and smoke haze pollution recurs yearly. The fire-related policy problems are defined as smoke haze pollution, forest degradation and deforestation, and impacts on the rural sector. Some of the apparent major causes of the problems are identified. The estimate of area affected by fires in 1997/98 is revised from 9.7 million hectares to 11.7 million hectares. The fires that resulted in forest degradation and deforestation caused economic costs in the range of $1.62-2.7 billion. The costs of smoke haze pollution were in the range of $674-799 million, and probably higher because estimates for the economic impacts on Indonesian business activities were not available. The valuation of costs associated with carbon emissions indicates that these may amount to as much as $2.8 billion. The revised estimates of economic costs from fires and smoke haze are still substantial and point to significant problems to be addressed to avoid similar impacts. Detailed policy recommendations are presented.
TL;DR: In this article, the authors used a gas-only, simple reflecting layer radiative transfer model to estimate the best fit altitudes of 18 bright features seen on the disk of Neptune and set a constraint on the fraction of hydrogen in ortho/para equilibrium.
TL;DR: In this article, the authors studied the impact of the South Asian haze on global climate variability and used a general circulation model to study the impacts of the SA haze on the global climate.
Abstract: Aerosols are regionally concentrated and are subject to large temporal variations, even on interannual timescales. In this study, the focus is on the observed large interannual variability of the South Asian (SA) haze, estimating the corresponding variations in its radiative forcing, and using a general circulation model to study their impacts on global climate variability. The SA haze is a widespread haze, covering most of South Asia and the northern Indian Ocean during December–April. The southernmost extent of the haze varies year to year from about 10°S to about 5°N. In order to understand the impact of this interannual variation in the haze forcing, two numerical studies were conducted with two extreme locations of the forcing: 1) extended haze forcing (EHF) and 2) shrunk haze forcing (SHF). The former has the forcing extending to 10°S, while the latter is confined to regions north of the equator. Each of the two haze forcing simulations was implemented into a 3D global climate model (NCAR C...
TL;DR: In situ observations of aerosols and trace gases and their physical and chemical characteristics were collected on board South African Weather Service Aerocommander research aircraft in this paper, showing a surprising degree of consistency in the observed vertical structure of the lower troposphere.
Abstract: [1] Episodes of regionally extensive haze were observed over southern African during the dry season intensive of the Southern African Regional Science Initiative (SAFARI 2000). Several case studies of southern African haze layers were examined and characterized in terms of physical structure as they exited off of the eastern coastal region of southern Africa. In situ observations of aerosols and trace gases and their physical and chemical characteristics were collected on board South African Weather Service Aerocommander research aircraft. Haze structure, based on these measurements, is examined as it varies with synoptic type. Despite strong differences in the observed ENSO regime between SAFARI 2000 and that observed during the Southern African Fire-Atmosphere Research Initiative (SAFARI-92) and their respective aerosol accumulation mechanisms (col Rrgions/weak anticyclones versus strong anticyclones), a surprising degree of consistency in the observed vertical structure of the lower troposphere was found in southern Africa. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry; 0368 Atmospheric Composition and Structure: Troposphere—constituent transport and chemistry; KEYWORDS: haze layers, synoptic circulations, ENSO
Journal Article•
TL;DR: In this article, a detailed characterization of carbonaceous particle types in smoke plumes from biomass fires and in regional hazes in southern Africa were studied using analytical transmission electron microscopy (TEM).
Abstract: Individual aerosol particles in smoke plumes from biomass fires and in regional hazes in southern Africa were studied using analytical transmission electron microscopy (TEM), which allowed detailed characterization of carbonaceous particle types in smoke and determination of changes in particle properties and concentrations during smoke aging. Based on composition, morphology, and microstructure, three distinct types of carbonaceous particles were present in the smoke: organic particles with inorganic (K-salt) inclusions, tar ball particles, and soot. The relative number concentrations of organic particles were largest in young smoke, whereas tar balls were dominant in a slightly aged (∼1 hour) smoke from a smoldering fire. Flaming fires emitted relatively more soot particles than smoldering fires, but soot was a minor constituent of all studied plumes. Further aging caused the accumulation of sulfate on organic and soot particles, as indicated by the large number of internally mixed organic/sulfate and soot/sulfate particles in the regional haze. Externally mixed ammonium sulfate particles dominated in the boundary layer hazes, whereas organic/sulfate particles were the most abundant type in the upper hazes. Apparently, elevated haze layers were more strongly affected by biomass smoke than those within the boundary layer. Based on size distributions and the observed patterns of internal mixing, we hypothesize that organic and soot particles are the cloud-nucleating constituents of biomass smoke aerosols. Sea-salt particles dominated in the samples taken in stratus clouds over the Atlantic Ocean, off the coast of Namibia, whereas a distinct haze layer above the clouds consisted of aged biomass smoke particles.