SINGAPORE - Is the haze back? The thought crossed the minds of many people in Singapore when the skies turned grey and a burning smell lingered in the air on Tuesday (March 29) afternoon.

The three-hour Pollutant Standards Index (PSI) reading hit 87 from 8pm. It fell to 83 at 10pm.

The reading had been rising steadily throughout the day, and ranged from 67 to 87.

As of 9pm, the 24-hour PSI reading was 65 to 79, which is in the moderate range.

A 24-hour PSI reading of 0 to 50 means air quality is in the good range, while a reading of 51 to 100 means it is in the moderate range.

The PSI has hovered nearer 40 to 60 in recent months, and this is the first noticeable spike this year.

People in Singapore have, however, noticed a burning smell in the air on some days in recent months.

Experts have told The Straits Times it is unlikely to have been caused by transboundary haze. There are few hot spots in Malaysia and Riau, Indonesia for now, the report on March 17 said.

The weather forecast said that prevailing winds are expected to be from the north or north-west, and become light and variable.

Haze is generally blown in by south-westerly winds.

Singapore suffered from one of its worst bouts of haze last year with the extended El Nino season.

Primary and secondary schools in Singapore were closed last September, as PSI readings reached hazardous levels.