HAZE

Haze is an atmospheric phenomenon where dust, smoke and other pollutant particles obscure the normal clarity of the sky. It 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.
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 is brownish, while mist is bluish-grey. While haze formation takes place in relatively dryish air, mist formation is in humid air. However, one complication is that haze particles can act as condensation nuclei for mist droplets.

Haze In Southeast Asia

Haze is a regular problem in Southeast Asia caused by land and forest fires in Indonesia, especially Sumatra and Kalimantan. Farmers and plantation owners are usually responsible for the fires, which they use to clear tracts of land for further plantings. Those fires mainly affect Brunei, Indonesia, Philippines, Malaysia, Singapore and Thailand, and occasionally Guam and Saipan[1] [2] The economic losses of the fires in 1997 have been estimated at US$9.3 billion [3]. This includes damages in agriculture production, destruction of forest lands, health, transportation, tourism, and other economic endeavours. Not included are social, environmental, and psychological problems and long-term health effects. The latest bout of haze to occur in Malaysia, Singapore and the Malacca Straits is in October 2006, and was caused by smoke from fires in Indonesia being blown across the Straits of Malacca by south-westerly winds.

Singapore's Downtown Core on 7 October 2006, when it was affected by forest fires in Sumatra, Indonesia.
The Association of Southeast Asian Nations (ASEAN) reacted and signed Agreement on Transboundary Haze Pollution, formed a Regional Haze Action Plan (RHAP) and established a co-ordination and support unit (CSU). RHAP, with the help of Canada, established a monitoring and warning system for forest/vegetation fires and implemented a Fire Danger Rating System (FDRS). The Malaysian Meteorological Service (MMS) [4] has issued a daily rating since September 2003. The Indonesians have been ineffective at enforcing legal policies on errant farmers.

Pollution Index

The severity of haze is often measured using automated optical instruments such as Nephelometers, as haze is associated with visibility and traffic control in ports. Haze however can also be an indication of poor air quality though this is often better reflected using accurate purpose built air indexes such as the American Air Quality Index, the Malaysian API (Air Pollution Index) and the Singaporean Pollutant Standards Index.
In hazy conditions, it is likely that the index will report the suspended particulate level. The disclosure of the responsible pollutant is mandated in some jurisdictions.
The American AQI is divided into six color coded categories. Technically AQI runs only from 0 to 500. The 301 to 500 range is categorised as hazardous and colored maroon. [5]
The Malaysian API does not have a capped value; hence its most hazardous readings can go above 500. Above 500, a state of emergency is declared in the affected area. Usually, this means that non-essential government services are suspended, and all ports in the affected area are closed. There may also be prohibitions on private sector commercial and industrial activities in the affected area excluding the food sector. So far, state of emergency rulings due to hazardous API levels were applied to the Malaysian towns of Port Klang, Kuala Selangor and the state of Sarawak during the 2005 Malaysian haze and the 1997 Southeast Asian haze.