The United States National Aeronautics and Space Administration (NASA) recently released satellite images of the smoke produced by forest fires in Sumatra and Borneo on September 24.

24-hour PSI levels in Singapore exceeded the hazardous range (above 300) at 4am on Friday September 25, a day after the above image was taken.

In the article, NASA also shared an image pin-pointing the hot spots in Sumatra:

In its report, NASA said "scientists monitoring the fires are concerned that the problem will get worse before it gets better," due to the El Niño, which lengthened periods of dry weather and reduced rainfall.

According to air particle data collected, particle levels are similar to the peaks recorded in 2006. This time, though, it is happening several weeks earlier in the dry season. If the forecasts for a longer dry season hold, 2015 may rank among the most severe haze events on record.

To make things worse, the forest fires in Sumatra and Borneo are unlike conventional ones and are difficult to put out, said NASA. The flames smoulder under the surface for long periods, "often for months".

The root cause? NASA believes it is large deposits of peat — a soil-like mixture of partly decayed plant material formed in wetlands — lining the coast of Borneo and Sumatra. According to David Gaveau, from the Center for International Forestry Research, "most burning starts on idle, already-cleared peatlands and escapes underground into an endless source of fuel."

If you'd like to see how this compares with two years ago, take a look at this satellite image of forest fires in Sumatra in June 2013, which saw PSI levels crossing 400 in Singapore:

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Realistic hourly PSI readings that reflect the haze level you see available at this website

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