2006 Southeast Asian haze

The 2006 Southeast Asian haze event was caused by continued uncontrolled burning from "slash and burn" cultivation in Indonesia, and affected several countries in the Southeast Asian region and beyond, such as Malaysia, Singapore, southern Thailand, and as far as Saipan; the effects of the haze may have spread to South Korea. Local sources of pollution partly contributed to the increased toxicity, particularly in high-pollution areas such as ports, oil refineries, and dense urban areas. In the highly urbanised and industrialised Klang Valley of Malaysia in particular, the surrounding terrain acted as a natural retainer of polluted air, aggravating the situation when the haze set in.

There is also a link to El Niño. The haze was made worse than during previous occurrences by the El Niño-Southern Oscillation which delayed the year's monsoon season. Fires in Kalimantan produce great amounts of smoke, burn a long time and are difficult to extinguish because they are on peatland, and once lit the fires can burn for months and release gases that produce sulphuric acid.

Air quality across the region appeared to improve in late October as heavy rainfall doused fires in Indonesia.

Brunei, an independent sultanate that is surrounded by East Malaysia's Sarawak state on Borneo, had been affected by the haze from Kalimantan. Rains brought some relief, and on 8 October, the Pollutant Standards Index had dropped to 46, which is within the "good" range. There was a brief spell of clear skies during the first week of Hari Raya, following a spell of rainy weather. But the haze returned on 31 October, with the Department of Environment, Parks and Recreation recording a PSI of 49.

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