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Haze often occurs when dust and smoke particles accumulate in relatively dry air. When weather conditions block the dispersal of smoke and other pollutants they concentrate and form a usually low-hanging shroud that impairs visibility and may become a respiratory health threat. Industrial pollution can result in dense haze, which is known as smog. Since 1 991, haze has been a particularly acute problem in Southeast Asia, Indonesian forest fires burnt to clear land being the reason. In response to the 1997 Southeast Asian haze, the SEAN countries agreed on a Regional Haze Action Plan (1997).
In 2002, all SEAN countries except Indonesia signed the Agreement on Turnarounds Haze Pollution, but the pollution is still a problem today. Under the agreement the SEAN secretariat hosts a co-ordination and support unit. CA] In the United States, the Interagency Monitoring of Protected Visual Environments (IMPROVE) program was developed as a collaborative effort between the US EPA and the National Park Service in order to establish he chemical composition of haze in National Parks and establish air pollution control measures in order to restore the visibility to pre-industrial levels. 3] Additionally, the Clean Air Act requires that any current visibility problems be remedied, and future visibility problems be prevented, in 156 Class I Federal areas located throughout the United States. A full list of these areas is available on Pea’s website. CA] Obscuration[edit] Haze causes issues in the area of terrestrial photography, where the integration of large amounts of dense atmosphere may be necessary to image distant subjects. This results in the visual effect of a loss of contrast in the subject, due to the effect of light scattering through the haze particles.
For these reasons, sunrise and sunset colors appear subdued on hazy days, and stars may be obscured at night. In some cases, attenuation by haze is so great that, toward sunset, the sun disappears altogether before reaching the horizon. CA] Haze can be defined as an aerial form of the Tyndale effect Hereford unlike other atmospheric effects such as cloud and fog, haze is spectrally selective: shorter (blue) wavelengths are scattered more, and longer (red/infrared) wavelengths are scattered less.