SINGAPORE - Air quality has worsened with the three-hour Pollutant Standards Index (PSI) climbing to the unhealthy level of 147 as of 6pm on Monday.

The latest PSI reading at 6am on Tuesday, Oct 7, is at 89.

It has been hazy in Singapore since the late morning on Monday, the National Environment Agency (NEA) said in an advisory.

Source: National Environment Agency

When it is in the unhealthy range of above 100, people should cut down and avoid prolonged or strenuous outdoor physical activity, especially the elderly, pregnant women, children and people with chronic lung or heart diseases. At moderate levels of between 50 to 100, normal activities can still be carried out.

The NEA also said in its advisory that there are elevated levels of PM2.5 (small, toxic particles) in all parts of Singapore, with an especially high one-hour concentration in the southern part of Singapore. Southwesterly winds have blown in smoke haze from a nearby source in central Sumatra. The hazy conditions are expected to continue on Tuesday and overall air quality for the next 24 hours is expected to be in the high end of the moderate and unhealthy range.

The PSI measures soot, dust particles, sulphur dioxide, carbon monoxide, nitrogen dioxide and ground level ozone in the air.