Showing papers on "Haze published in 2001"

Indian Ocean Experiment: An integrated analysis of the climate forcing and effects of the great Indo-Asian haze

Abstract: Every year, from December to April, anthropogenic haze spreads over most of the North Indian Ocean, and South and Southeast Asia. The Indian Ocean Experiment (INDOEX) documented this Indo-Asian haze at scales ranging from individual particles to its contribution to the regional climate forcing. This study integrates the multiplatform observations (satellites, aircraft, ships, surface stations, and balloons) with one- and four-dimensional models to derive the regional aerosol forcing resulting from the direct, the semidirect and the two indirect effects. The haze particles consisted of several inorganic and carbonaceous species, including absorbing black carbon clusters, fly ash, and mineral dust. The most striking result was the large loading of aerosols over most of the South Asian region and the North Indian Ocean. The January to March 1999 visible optical depths were about 0.5 over most of the continent and reached values as large as 0.2 over the equatorial Indian ocean due to long-range transport. The aerosol layer extended as high as 3 km. Black carbon contributed about 14% to the fine particle mass and 11% to the visible optical depth. The single-scattering albedo estimated by several independent methods was consistently around 0.9 both inland and over the open ocean. Anthropogenic sources contributed as much as 80% (±10%) to the aerosol loading and the optical depth. The in situ data, which clearly support the existence of the first indirect effect (increased aerosol concentration producing more cloud drops with smaller effective radii), are used to develop a composite indirect effect scheme. The Indo-Asian aerosols impact the radiative forcing through a complex set of heating (positive forcing) and cooling (negative forcing) processes. Clouds and black carbon emerge as the major players. The dominant factor, however, is the large negative forcing (-20±4 W m^(−2)) at the surface and the comparably large atmospheric heating. Regionally, the absorbing haze decreased the surface solar radiation by an amount comparable to 50% of the total ocean heat flux and nearly doubled the lower tropospheric solar heating. We demonstrate with a general circulation model how this additional heating significantly perturbs the tropical rainfall patterns and the hydrological cycle with implications to global climate.

Comparison of laser beam propagation at 785 nm and 1550 nm in fog and haze for optical wireless communications

Abstract: 12 There is currently a misconception among designers and users of free space laser communication (lasercom) equipment that 1550 nm light suffers from less atmospheric attenuation than 785 or 850 nm light in all weather conditions. This misconception is based upon a published equation for atmospheric attenuation as a function of wavelength, which is used frequently in the free-space lasercom literature. In hazy weather (visibility > 2 km), the prediction of less atmospheric attenuation at 1550 nm is most likely true. However, in foggy weather (visibility < 500 m), it appears that the attenuation of laser light is independent of wavelength, ie. 785 nm, 850 nm, and 1550 nm are all attenuated equally by fog. This same wavelength independence is also observed in snow and rain. This observation is based on an extensive literature search, and from full Mie scattering calculations. A modification to the published equation describing the atmospheric attenuation of laser power, which more accurately describes the effects of fog, is offered. This observation of wavelength-independent attenuation in fog is important, because fog, heavy snow, and extreme rain are the only types of weather that are likely to disrupt short (< 500 m) lasercom links. Short lasercom links will be necessary to meet the high availability requirements of the telecommunications industry.

Instant dehazing of images using polarization

Abstract: We present an approach to easily remove the effects of haze from images. It is based on the fact that usually airlight scattered by atmospheric particles is partially polarized. Polarization filtering alone cannot remove the haze effects, except in restricted situations. Our method, however, works under a wide range of atmospheric and viewing conditions. We analyze the image formation process, taking into account polarization effects of atmospheric scattering. We then invert the process to enable the removal of haze from images. The method can be used with as few as two images taken through a polarizer at different orientations. This method works instantly, without relying on changes of weather conditions. We present experimental results of complete dehazing in far from ideal conditions for polarization filtering. We obtain a great improvement of scene contrast and correction of color. As a by product, the method also yields a range (depth) map of the scene, and information about properties of the atmospheric particles.

Martian dust storms: 1999 Mars Orbiter Camera observations

Abstract: The Mars Orbiter Camera on board the Mars Global Surveyor from March 9, 1999 (Ls = 107°, where Ls is the areocentric longitude of the Sun measured in degrees from Mars' northern spring equinox), to December 31, 1999 (Ls = 274°), has obtained 7.5 km pixel−1 daily global maps of the Martian surface in two wavelength bands: blue (400–450 nm) and red (575–625 nm). Visual inspection of these maps during the 1999 dust storm season has resulted in the detection of 783 dust storms, ranging in size from “local” (>102 km2) to “regional” (>1.6×106 km2). No global storms were observed. The difference in the numbers of dust storms occurring in the two hemispheres (north: 343; south: 440) was not statistically significant. Fifty percent of the regional size dust storms formed as a result of the “merger” of two or more smaller local storms. The regional storms from Ls = 207° to Ls = 223° were observed to move from the northern hemisphere into the southern hemisphere between 30°W and 50°W longitude. This cross-equatorial transport of dust suggests the location of the low-lying southward flowing branch of the Hadley circulation. Observations show that dust storms occur in several regions on Mars: at the two polar cap edges, at the base of high elevation regions in the northern hemisphere, near the polar hood during northern fall, and at mid-latitudes in both hemispheres. Specific regions such as Solis Planum and Hesperia, which were regions of significant dust activity in the past, showed almost no dust storm activity in 1999, suggesting that regional dust sources are variable over a 20-year time frame. One region of exceptional activity not noted previously was the Arcadia-Amazonis border. However, other regions, such as near Elysium Mons, Acidalia, Chryse, Hellas, Noachis, Argyre, Cimmeria, and Sirenum, again were active dust storm regions. Relative dust opacities were modeled for 117 red wavelength events and ranged from 0.54 “diffuse haze” to 2.13 “concentrated local events.” From the dust opacities we estimated the north polar sedimentation rate to be 6.0–10×10−4 g cm−2 yr−1, a factor of 40 smaller than previous estimates from the two 1977 global dust storms [Pollack et al., 1979], along with the global dust mass loading (2.6–4.0×10−4 g cm−2) and cross-equatorial dust mass loading (3.6×10−4 g cm−2). The 1999 cross-equatorial mass dust loading suggests that the southern hemisphere subtropical latitudes require at least 2–3 Martian years to replenish their dust sources before global storms can form.

UV shielding of NH3 and O2 by organic hazes in the Archean atmosphere

Abstract: The late Archean atmosphere was probably rich in biologically generated CH4 and may well have contained a hydrocarbon haze layer similar to that observed today on Saturn's moon, Titan. Here we present a detailed model of the photochemistry of haze formation in the early atmosphere, and we examine the effects of such a haze layer on climate and ultraviolet radiation. We show that the thickness of the haze layer was limited by a negative feedback loop: A haze optical depth of more than ∼0.5 in the visible would have produced a strong “antigreenhouse effect,” thereby cooling the surface and slowing the rate at which CH4 was produced. Given this climatic constraint on its visible optical depth, the amount of UV shielding provided by the haze can be estimated from knowledge of the optical properties and size distribution of the haze particles. Contrary to previous studies [Sagan and Chyba, 1997], we find that when the finite size of the particles is taken into account, the amount of UV shielding provided by the haze is small. Thus NH3 should have been rapidly photolyzed and should not have been sufficiently abundant to augment the atmospheric greenhouse effect. We also examine the question of whether photosynthetically generated O2 could have accumulated beneath the haze layer. For the model parameters considered here, the answer is “no”: The upper limit on ground level O2 concentrations is ∼10−6 atm, and a more realistic estimate for pO2 during the late Archean is 10−8 atm. The stability of both O2 and NH3 is sensitive to the size distribution and optical properties of the haze particles, neither of which is well known. Further theoretical and laboratory work is needed to address these uncertainties.

Long-range transport of Asian dust to the Lower Fraser Valley, British Columbia, Canada

Abstract: For the first time, long-range transport of “Kosa” mineral aerosol from western China to southwestern British Columbia is documented. This late April 1998 event coincided with an episode of photochemical smog and reduced dispersion in the Lower Fraser Valley (LFV). Filter samples in the region show a massive injection of crustal elements (Si, Fe, Al, and Ca) with concentrations of Si approximately double those previously recorded. Ratios of these elements to Fe are shown to be statistically similar to ratios observed in mineral aerosol events in Hawaii and China. On the basis of the difference between observed and expected elemental concentrations and reconstructed soil mass in the episode, it is estimated that Asian dust contributed 38–55% to observed PM10 in the LFV, the remainder being attributed to local sources. Comparison of the April 1998 event with two spring meteorological analogs is consistent with this estimate. Mesoscale model simulations suggest that mineral dust was incorporated into the planetary boundary layer as a result of strong subsidence over the interior of southern British Columbia and Washington State which permitted interception of lower tropospheric elevated aerosol layers by surface-based mixing processes over mountainous terrain. Surface easterly (“outflow”) winds then transported this material into the Lower Fraser Valley where it contributed significantly to total particulate loadings and an intense haze. This mechanism is consistent with the observed spatial and temporal distribution of PM10.

Dust in the Wind: Long Range Transport of Dust in the Atmosphere and Its Implications for Global Public and Ecosystem Health

Abstract: Movement of soil particles in atmospheres is a normal planetary process. Images of Martian dust devils (wind-spouts) and dust storms captured by NASA's Pathfinder have demonstrated the significant role that storm activity plays in creating the red atmospheric haze of Mars. On Earth, desert soils moving in the atmosphere are responsible for the orange hues in brilliant sunrises and sunsets. In severe dust storm events, millions of tons of soil may be moved across great expanses of land and ocean. An emerging scientific interest in the process of soil transport in the Earth's atmosphere is in the field of public and ecosystem health. This article will address the benefits and the potential hazards associated with exposure to particle fallout as clouds of desert dust traverse the globe.

Satellite detection of a continental-scale plume of nitrogen oxides from boreal forest fires.

Abstract: In previous studies it was shown that boreal forest fires in Canada caused large plumes with high CO and aerosol concentrations in August 1998. Haze and enhanced CO and O 3 were observed even over Europe. In this study we use dispersion model calculations, Total Ozone Mapping Spectrometer (TOMS) aerosol index data, and tropospheric NO 2 columns derived from Global Ozone Monitoring Experiment (GOME) data to track a NO x plume from forest fire hot spots, via the Atlantic Ocean, to the west coast of Europe.

Organic haze in Earth's early atmosphere: Source of low-13C Late Archean kerogens?

Abstract: High concentrations of greenhouse gases would have been required to offset low solar luminosity early in Earth9s history. Enhanced CO 2 levels are probably at least part of the solution, but CH 4 may have played a significant role as well, particularly during the Late Archean era, 2.5–3.0 Ga, when methanogenic bacteria were almost certainly present. Indeed, biological CH 4 production should have led to CO 2 drawdown by way of a negative feedback loop involving the carbonate-silicate geochemical cycle. We suggest here that the atmospheric CH 4 /CO 2 ratio approached the value of ∼1 needed to trigger formation of Titan-like organic haze. This haze was strongly depleted in 13 C relative to 12 C and was produced at a rate comparable to the modern rate of organic carbon burial in marine sediments. Therefore, it could provide a novel explanation for the presence of extremely low- 13 C kerogens in Late Archean sediments.

Forest fires and regional Haze in Southeast Asia

Abstract: The fires and resulting air pollution which afflicted Southeast Asia in 1997 and 1998 were a major environmental disaster affecting the livelihood and health of the people of the region, destroying forest and wildlife resources, releasing greenhouse gases and having serious implications for the rich biodiversity of the islands of Borneo and Sumatra Individual chapters have been contributed by international experts and cover a range of issues The relation of the El Nino effect to droughts and fires is discussed and the history of fires in the region is outlined Although the fires were associated with long periods of drought, in most cases they had human causes, and the land and forest management policies responsible for them are also identified Another chapter describes the important role remote sensing played in monitoring and locating the fires and haze Other contributions are concerned with the chemistry of haze, the long-range transport of pollutants and their modelling, the effects on forest ecosystems, and the implications for global climate change Health impacts of the air pollution are discussed and the costs in economic terms are analysed The inability of the Indonesian government to control the fires, the public responses to pollution problems and efforts at international co-operation are also discussed, as is the portrayal of the issues in the media

UV 380 nm reflectivity of the Earth's surface, clouds and aerosols

Abstract: The 380 nm radiance measurements of the Total Ozone Mapping Spectrometer (TOMS) have been converted into a global data set of daily (1979–1992) Lambert equivalent reflectivities R of the Earth's surface and boundary layer (clouds, aerosols, surface haze, and snow/ice) and then corrected to RPC for the presence of partly clouded scenes. Since UV surface reflectivity is between 2 and 8% for both land and water during all seasons of the year (except for ice and snow cover), reflectivities larger than the surface value indicate the presence of clouds, haze, or aerosols in the satellite field of view. A statistical analysis of 14 years of daily reflectivity data shows that most snow-/ice-free scenes observed by TOMS have a reflectivity less than 10% for the majority of days during a year. The 380 nm reflectivity data show that the true surface reflectivity is 2–3% lower than the most frequently occurring reflectivity value for each TOMS scene as seen from space. Most likely the cause is a combination of frequently occurring boundary layer water and/or aerosol haze. For most regions the observation of extremely clear conditions needed to estimate the surface reflectivity from space is a comparatively rare occurrence. Certain areas (e.g., Australia, southern Africa, portions of northern Africa) are cloud-free more than 80% of the year, which exposes these regions to larger amounts of UV radiation than at comparable latitudes in the Northern Hemisphere. Regions over rain forests, jungle areas, Europe and Russia, the bands surrounding the Arctic and Antarctic regions, and many ocean areas have significant cloud cover (R>15%) more than half of each year. In the low to middle latitudes the areas with the heaviest cloud cover (highest reflectivity for most of the year) are the forest areas of northern South America, southern Central America, the jungle areas of equatorial Africa, and high mountain regions such as the Himalayas or the Andes. The TOMS reflectivity data show both the presence of large nearly clear ocean areas and the effects of the major ocean currents on cloud production.

Process for converting waxy feeds into low haze heavy base oil

Abstract: The present invention discloses a process for producing a low haze heavy base oil including the steps of: (a) providing a heavy waxy feed stream having an initial boiling point greater than 900° F. and having a paraffin content of at least 80%; (b) separating the heavy feed stream into a heavy fraction and a light fraction by a deep cut distillation; and (c) hydroisomerizing the light fraction to produce a low haze heavy base oil.

Seasonal characteristics of haze observed by continuous visibility monitoring in the urban atmosphere of Kwangju, Korea.

Abstract: Continuous visibility monitoring has been carried out inKwangju, Korea since May 1999. The total light extinctioncoefficient bext measured by a transmissometer andreveals seasonal trends in urban visual air quality,especially under hazy conditions with a visual range of lessthan 15 km. Seasonal atmospheric visibility under lowrelative humidity during the winter was observed to be betterthan during any other seasons. Summertime visibility wasseverely degraded due to highly increased light scattering byhygroscopic particles under high humidity atmosphericconditions. Visibility during spring and fall was alsomoderate. However, yellow sand in spring caused the lowestvisibility conditions over the measurement area for a fewdays. With continuous monitoring using the transmissometer,the daily average seasonal visual range was measured to be13.1, 9.2, 11.0, and 13.9 km in spring, summer, falland winter, respectively. Under the atmospheric humiditycondition less than 60%, visual range was observed tobe 16.1, 13.9, 15.1, and 16.6 km in spring, summer,fall, and winter, respectively. The mean light extinctionbudget by sulfate and nitrate aerosols was determined to bethe highest value of 63.71% during the summer and thelowest value of 27.08% during spring. During the `yellow sand dust' period, a mean light extinction budget by soil particles was estimated to be at an unusually high value of 44.22%.

Changes to the surface level solar ultraviolet-B radiation due to haze perturbation

Abstract: The South-East Asian region experienced a haze episode in 1994 which was widely believed to be due to widespread forest fires in Sumatra and Kalimantan (Indonesia). Broadband measurements of the surface level solar ultraviolet-B, UV-A and Global radiation at Penang (Malaysia) are used to study the effect of the 1994 haze on effective UV-B irradiance. We find that during the haze episode, there is enhanced absorption of surface level UV-B radiation. The effect of haze on UV-A and Global radiation is much less. The reduction in absolute noon time UV-B irradiance (mostly cloud free) during the 1994 haze period was 23% relative to the UV-B irradiance during thecorresponding haze-free period in 1995. Even though the noon time radiation data minimizes the cloud effect in the results presented some cloud effect is still present.

Haze and Health in Brunei Darussalam: The Case of the 1997‐98 Episodes

Abstract: A study of the impacts of the 1997-98 haze episodes in Brunei Darussalam was carried out in two districts between September 1997 and September 1998 through random surveys of households. The aim of the study was to understand health problems caused by haze; whether such health impacts differed amongst different groups in the population; and the nature of the differences that might exist. The study also sought to understand whether health impacts of haze varied between urban and rural areas. Furthermore, the study aimed to understand respondents' perception of the haze problem. Some hypotheses formulated to establish the existence or otherwise of significant difference between health conditions during haze (September 1997 and January-June 1998) and haze-free periods (January-June 1997 and September 1998) were verified through the p-value statistical approach. The conclusions from the verifications are that adverse health effects of the haze were statistically significant and were not uniform with respect to different groups in the population. For example, the deleterious effects of haze appeared skewed towards the young (age 1-5 years) and the aged (≥60 years). A higher proportion of urban population was more adversely affected than in rural areas and, other things being equal, a higher proportion of outdoor workers was more adversely affected by haze than their indoor counterparts. The paper suggests cooperative efforts amongst ASEAN governments to reduce poverty in communities that burn forests; improve their socioeconomic opportunities; lessen their dependence on land; and share information related to haze to prevent or mitigate its adverse effects. There is a need to intervene especially in the private sector with respect to work schedules of those who work outdoors (e.g. construction workers) and the housing of immigrant workers occupying makeshift structures to escape rents in proper accommodation. There is also a need for greater and sustained programme of educating the public on environmental hazards to mitigate their adverse impacts on society.