Under the agreement, the ASEAN secretariat hosts a co-ordination and support unit. In 2002, all ASEAN countries signed the Agreement on Transboundary Haze Pollution, but the pollution is still a problem there today. ![]() In response to the 1997 Southeast Asian haze, the ASEAN countries agreed on a Regional Haze Action Plan (1997) as an attempt to reduce haze. The main source of the haze has been smoke from fires occurring in Sumatra and Borneo which dispersed over a wide area. ![]() Since 1991, haze has been a particularly acute problem in Southeast Asia. Industrial pollution can result in dense haze, which is known as smog. 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 if excessively inhaled. Haze often occurs when suspended dust and smoke particles accumulate in relatively dry air. Large areas of haze covering many thousands of kilometers may be produced under extensive favorable conditions each summer. For all these reasons, wet haze tends to be primarily a warm-season phenomenon. A small component of wet-haze aerosols appear to be derived from compounds released by trees when burning, such as terpenes. The reactions are enhanced in the presence of sunlight, high relative humidity, and an absence of air flow (wind). Such aerosols commonly arise from complex chemical reactions that occur as sulfur dioxide gases emitted during combustion are converted into small droplets of sulfuric acid when exposed. ![]() In meteorological literature, the word haze is generally used to denote visibility-reducing aerosols of the wet type suspended in the atmosphere. However, haze particles may act as condensation nuclei that leads to the subsequent vapor condensation and formation of mist droplets such forms of haze are known as "wet haze". Whereas haze often is considered a phenomenon occurring in dry air, mist formation is a phenomenon in saturated, humid air. an approaching airplane) and depending on the direction of view with respect to the Sun, haze may appear brownish or bluish, while mist tends to be bluish grey instead. Sources for particles that cause haze include farming ( ploughing in dry weather), traffic, industry, windy weather, volcanic activity and wildfires. The World Meteorological Organization manual of codes includes a classification of particulates causing horizontal obscuration into categories of fog, ice fog, steam fog, mist, haze, smoke, volcanic ash, dust, sand, and snow. Haze is traditionally an atmospheric phenomenon in which dust, smoke, and other dry particulates suspended in air obscure visibility and the clarity of the sky. Haze causing red sky, due to the scattering of light on smoke particles, also known as Rayleigh scattering during Mexico's forest fire season Haze in Monterrey, Mexico, during grassland fires ![]() Bushfire haze in Sydney, Australia Haze as smoke pollution over the Mojave from fires in the Inland Empire, June 2016, demonstrates the loss of contrast to the Sun, and the landscape in general. Haze over the Mojave Desert from a brush fire in Santa Barbara, California, seen as the Sun descends on the 2016 June solstice, allows the Sun to be photographed without a filter.
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