The three-hour Pollutant Standards Index (PSI) at 6pm on Saturday remains at 73, the lowest reading since last Sunday morning.

The 24 hour average PSI at 6pm also dipped to a 162-184 range from 165-185.

Air in the 51-100 reading is considered "moderate", while the 101 to 200 PSI range is considered "unhealthy". Anything above 300 is hazardous, while readings between 201 and 300 are very unhealthy.

However it may still be too soon to put away the face masks.

The National Environment Agency (NEA) said during a technical briefing on Saturday evening that they expect the 24-hour PSI for Sunday to remain in the "Very Unhealthy" band of 201-300. Healthy people are advised to avoid prolonged outdoor physical exertion, and to wear an N95 mask when outdoors. Elderly, pregnant women, children and those with chronic respiratory or heart ailments should avoid all outdoor activity and wear a N95 mask when outside.

In addition, while the PSI is in the "moderate" range, readings of PM2.5, particles which are 2.5 microns or smaller, remain high at 211 - 249. According to the NEA, once PM2.5 readings cross 40, the public should limit prolonged or heavy exertion outdoors. When readings are more than 150, everyone should avoid all physical activity outdoors.

Due to their small size, PM2.5 particles easily bypass the nasal system and can penetrate deep into the lungs, making them more toxic. PM2.5 readings are not accounted for in the PSI, but measured separately.