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Motorists ply along Singapore's central expressway blanketed by smog from agricultural fires in neighbouring Sumatra island in Indonesia on September 29, 2015. The Pollutant Standards Index, which measures air quality, climbed to 'very unhealthy' levels in Singapore, according to the National Environment Agency. AFP PHOTO / ROSLAN RAHMAN (Photo credit should read ROSLAN RAHMAN/AFP/Getty Images)

Motorists ply along Singapore's central expressway blanketed by smog from agricultural fires in neighbouring Sumatra island in Indonesia on September 29, 2015.  The Pollutant Standards Index, which measures air quality, climbed to 'very unhealthy' levels in Singapore,  according to the National Environment Agency.      AFP PHOTO / ROSLAN RAHMAN        (Photo credit should read ROSLAN RAHMAN/AFP/Getty Images)