SINGAPORE - All over the island today, people basked in the clear skies in the afternoon - which appeared suddenly after the three-hour Pollutant Standards Index (PSI) reading hit 326 at 10am - and embraced the sunshine, some returning to their favourite outdoor activities after being cooped up to avoid the haze.

But the respite - which was attributed to a temporary change of wind conditions in Singapore - was to be short lived. At the daily briefing today, the National Environment Agency (NEA) said the good visibility - the quality of the air remained poor as the PM2.5 concentration was still much higher than the normal levels - would only last “a few hours”.At 4pm,the 24-hour PM2.5 concentration, or very fine particulate matter, was between 207 and 246 micrograms per cubic metre - much higher than the normal levels of between 20 and 40 micrograms per cubic metre - the authorities warned that the public should still be wearing N95 masks if prolonged or outdoor activity is unavoidable.

Ministry of the Environment and Water Resources Deputy Secretary Tan Gee Keow said: “This is yet another example of the three-hour PSI versus the 24-hour PSI readings. Within three hours, you may see blue skies but over time, these conditions will change.”

Referring to the Government’s advisories, Ms Tan said: “We’ve always given it based on 24-hour PSI, because that’s what the science and research is based on - the 24-hour exposure.”

The Singapore Metrological Service’s Patrica Ee explained that the change in wind conditions caused a “less-dense” portion of the haze plume to be blown over the Republic.

However, as dry weather conditions and winds blowing from the southwest or western direction continue to persist, hazy conditions are likely to return tomorrow.

Despite the respite, the NEA said that the 24hr PSI remained in the unhealthy range (201 to 300) today and it is expected to stay the same range tomorrow.

There were 118 hotspots detected today. There were only 19 detected yesterday but the low number was because of the thick cloud cover which affected the detection.

During the briefing, the Ministry of Health’s Group Director of Public Health Derrick Heng also allayed public concern that PM2.5 particulates would be lodged in the lungs and may lead to cancer.

He said: “It is true that some of the smaller particles may be absorbed in the lungs, and that’s where they may cause some irritation and inflammation… but I won’t go so far as to say that they will... be in (the lungs) forever.”

Ms Tan also reiterated that there are sufficient N95 masks “to go around nationally” and that there is no need for healthy persons to “go into a panic” and stockpile masks.

She said: “The reason why we are putting up the advisories and these air quality measurements is to make plain and transparent what’s going on. People should only buy masks when required as per some of the situations stated in the health advisories. If you are a healthy person, there is no need to stockpile.”

For tomorrow, the authorities advise healthy persons to avoid prolonged or strenuous outdoor physical exertion, while N95 masks are only required to be worn if strenuous activities outdoors cannot be avoided.

The elderly, pregnant women, and children as well as persons with chronic lung disease, heart disease or stroke should avoid outdoor activities and wear N95 masks if these are unavoidable.