There is also a link to El Niño.[3] 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.[4]