The PSI dropped down to 143 at 17:00 (09:00 GMT), although this is still classed as "unhealthy".
Before this week's episode, the previous air pollution record was from September 1997 during the 1997-1998 South East Asian Haze, when the PSI peaked at 226.
Singapore resident Nicole Wu told the BBC that she had stayed indoors for the past two days.
"It's terrible. In my flat the windows are all closed with the air conditioning on," she said. "My mother has to wear a mask to go shopping.