Haze
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225636794
2008-07-14T17:50:00Z
Bidgee
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{{Pollution}}
{{otheruses|Haze (disambiguation)}}
'''Haze''' is traditionally an [[Earth's atmosphere|atmospheric]] phenomenon where dust, smoke and other dry particles obscure the clarity of the sky. The [[WMO]] manual of codes includes a classification of horizontal obscuration into categories of [[fog]], [[ice fog]], [[steam fog]], [[mist]], haze, [[smoke]], [[vog|volcanic ash]], [[dust]], [[sand]] and [[snow]]. <ref>[http://www.wmo.ch/pages/prog/www/WMOCodes/Manual/WMO306_vol-I-2-PartB.pdf WMO Manual on Codes]</ref>
Sources for haze particles include farming (ploughing in dry weather), traffic, industry, forest fires and peat field fire.
Seen from afar (e.g. approaching airplane), haze appears brownish, while [[mist]] is bluish-grey. Whereas haze formation is a phenomenon of dry air, mist formation is a phenomenon of humid air. However, haze particles may act as condensation nuclei for later mist droplet formation.
'''Haze''' is also use to describe [[turbidity]] in clear glass or plastic as a percent value, or turbidity in [[beer]] or [[wine]].
==Air pollution==
{{main|smog}}
[[Image:32919747 ae077d271d o.jpg|thumb|left|Haze over Kuala Lumpur]]
[[Image:Adelaide River Hills.jpg|thumb|left|Smoke haze over hills near [[Adelaide River, Northern Territory]]]]
[[ Image:Getty 5 bg 081003.jpg|thumb|right|Los Angeles skyline, showing haze. ]]
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 [[Respiration (physiology)|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. In response the [[Association of Southeast Asian Nations|ASEAN countries]] agreed on a Regional Haze Action Plan (1997) and later signed the [[ASEAN Agreement on Transboundary Haze Pollution|Agreement on Transboundary Haze Pollution]] (2002). Under the agreement the ASEAN secretariat hosts a co-ordination and support unit.<ref>[http://www.haze-online.or.id/ ASEAN action hazeonline]</ref>
==Obscuration==
Haze causes issues in the area of terrestrial photography, where the penetration 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 [[particulate|particles]]. 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. For this reason many super-telephoto lenses often incorporate yellow [[filter (optics)|filters]] or coatings to enhance image contrast.
Infrared (IR) imaging may also be used to penetrate haze over long distances, with a combination of IR-pass optical filters (such as the [[Wratten number|Wratten 89B]]) and IR-sensitive detector.
==Turbidity==
With production of plastic films haze has technical significance as the percentage of light that is deflected more than 2.5° from the incoming light direction.<ref>[http://www.thermallamination.com/haze.php Haze technical definition]</ref>
==See also==
{{Commons|Haze}}
* [[Aerial perspective]]
* [[Arctic haze]]
* [[Saharan Air Layer]]
* [[Smog]]
==Notes==
{{reflist}}
==External links==
* [http://www.npi.gov.au/database/substance-info/profiles/69.html National Pollutant Inventory - Particulate matter fact sheet]
[[category:visibility]]
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[[nl:Heiig]]
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[[pt:Névoa seca]]
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[[simple:Haze]]
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