1997 Southeast Asian haze
The 1997 Southeast Asian haze was a large-scale air quality disaster that occurred during the second half of 1997, its after-effects causing widespread atmospheric visibility and health problems within Southeast Asia. The total costs of the Southeast Asian haze are estimated at US$9 billion, due mainly to health care and disruption of air travel and business activities.
The influence of the 1997 fires in Kalimantan and Sumatra on ambient air quality was evident by July and peaked in September/October before weakening by November, when the delayed monsoonal rain extinguished the fires and improved air quality within the region. During the peak episode, satellite imagery (NASA/TOMS aerosol index maps) showed a haze layer that expanded over an area of more than 3,000,000 km2 (1,200,000 sq mi), covering large parts of Sumatra and Kalimantan. Its northward extension partially reached Malaysia, Singapore, Brunei and Thailand. During this period, particulate matter concentrations frequently exceeded national ambient air quality standards. Monthly mean horizontal visibility at most locations in Sumatra and Kalimantan in September was below 1 km (0.62 mi) and daily maximum visibility was frequently below 100 metres (330 ft).
The 1997 Southeast Asian haze was caused mainly by slash-and-burn techniques adopted by farmers in Indonesia. Slash and burn has been extensively used for many years as the cheapest and easiest means to clear the lands for traditional agriculture. Fire is also used during the long fallow rotation of the so-called jungle rubber in Sumatra and Kalimantan to remove most of the biomass, including the woody parts before new plantations are re-established.
Fire may also be deliberately used as a weapon to claim property on the islands and provinces where land ownership is not clear, an action taken by both smallholders and large operators alike. After burning out its previous owner, the smallholder or large operator plants their own crops there, gaining de facto control over the disputed land.
...
Wikipedia