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Haze is traditionally an atmospheric phenomenon where dust, smoke and other dry particles obscure the clarity of the sky. The World Meteorological Organization manual of codes includes a classification of horizontal obscuration into categories of fog, ice fog, steam fog, mist, haze, smoke, volcanic ash, dust, sand and snow.〔(WMO Manual on Codes )〕 Sources for haze particles include farming (ploughing in dry weather), traffic, industry, and wildfires. Seen from afar (e.g. approaching airplane) and depending upon the direction of view with respect to the sun, haze may appear brownish or bluish, while mist tends to be bluish-grey. Whereas haze often is thought of as a phenomenon of dry air, mist formation is a phenomenon of humid air. However, haze particles may act as condensation nuclei for the subsequent formation of mist droplets; such forms of haze are known as "wet haze." The term "haze", in meteorological literature, generally is used to denote visibility-reducing aerosols of the wet type. Such aerosols commonly arise from complex chemical reactions that occur as sulfur dioxide gases emitted during combustion are converted into small droplets of sulphuric acid. The reactions are enhanced in the presence of sunlight, high relative humidity, and stagnant air flow. A small component of wet haze aerosols appear to be derived from compounds released by trees, such as terpenes. For all these reasons, wet haze tends to be primarily a warm-season phenomenon. Large areas of haze covering many thousands of kilometers may be produced under favorable conditions each summer. ==Air pollution== (詳細はvisibility and may become a respiratory health threat. Industrial pollution can result in dense haze, which is known as smog. Since 1991, haze has been a particularly acute problem in Southeast Asia. The main source of the haze has been fires occurring in Sumatra and Borneo. In response to the 1997 Southeast Asian haze, the ASEAN countries agreed on a Regional Haze Action Plan (1997). In 2002, all ASEAN countries except Indonesia signed the Agreement on Transboundary Haze Pollution, but the pollution is still a problem today. Under the agreement the ASEAN secretariat hosts a co-ordination and support unit.〔(ASEAN action hazeonline )〕 During the 2013 Southeast Asian haze, Singapore experienced a record high pollution level, with the 3-hour Pollution Standards Index reaching a record high of 401.〔(【引用サイトリンク】url=http://www.bbc.co.uk/news/world-asia-22998592 )〕 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 the chemical composition of haze in National Parks and establish air pollution control measures in order to restore the visibility to pre-industrial levels.〔(IMPROVE Visibility Program )〕 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 EPA's website.〔(Federal Class 1 Areas )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Haze」の詳細全文を読む スポンサード リンク
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