The three-hour PSI initially climbed steadily as it hit 215 as of 2pm but fell to 157 at 4pm.

The National Environment Agency has forecast that the overall 24-hour Pollutant Standards Index (PSI) reading over the next 12 hours is likely to remain in the high end of the “moderate” range.

The one-hour PM2.5 reading was highest in western Singapore at 1pm, at 188. It then dropped to 167 at 2pm, 111 at 3pm and 104 at 4pm.

NEA introduced new bandings and descriptors for the one-hour concentration readings of fine particles called PM2.5 -- a major pollutant in smoke haze in July this year.

This is to help the public better plan activities in real-time.

PM2.5 particles are one of six pollutants measured by the PSI but health advisories are still based on the 24-hour PSI reading, rather than shorter-term measures that can fluctuate over the course of the day.

The hourly PM2.5 reading for finer pollutants is also expected to remain in the “elevated” and “high” ranges over the next six to 12 hours.

NEA’s health advisory said that “everyone can continue with normal activities”.

The elderly and children, or those who are feeling unwell or suffering from chronic conditions, should seek medical attention.

According to the National Environment Agency, a value of 201-300 for 24-hour PSI falls in the very unhealthy range.

This latest bout of haze comes after Indonesia warned last Friday, Aug. 19, that haze from forest fires was floating over the Malacca Strait towards its neighbours.

The rising number of blazes is a result of the dry weather in the coming weeks that could make fire-fighting efforts more challenging.

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Realistic hourly PSI readings that reflect the haze level you see available at this website

Bad haze conditions bring the best out of S’poreans’ Photoshop skills

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