haze The haze occasionally experienced in Singapore is a form of smog (a compound word for smoke and fog). Atmospheric pollution creates solid hygroscopic particles which absorb moisture; this leads to condensation and the formation of a type of dirty, low- lying cloud. Haze is produced by the combination of a hot, humid climate and pollution from motor traffic and industry as well as the burning of vegetation in neighbouring countries. Haze is monitored by the National Environment Agency. A Pollutant Standards Index (PSI) is used to inform the public of haze pollution levels.

Haze is at its worst when El Niño occurs (every five to ten years)— the ocean currents in the Pacific reverse and Southeast Asia experiences drier than usual weather. During such periods, agricultural and forest fires in Indonesia and Malaysia can burn out of control. The most severe occurrence was in 1997, when forest fires raged on both Sumatra and Borneo. The PSI became dangerously high in Singapore and visibility was less than 2 km for 12 consecutive days.

Photo credit: Editions Didier Millet