SINGAPORE - The skies were grey on Tuesday as slight hazy conditions persisted through the day.

The three-hour Pollutant Standards Index (PSI) reading hit 91 at 10am, according to the National Environment Agency's (NEA) website.

It dipped to 79 at noon and 77 at 2pm. It was between 71 and 88 from 3am to 11am.

The 24-hour PSI reading was at 63 to 79, with the highest reading of 79 recorded in the west of Singapore.

Air quality remains in the moderate zone, and normal activities can go on as usual.

"Slightly hazy conditions can be expected on a few days, in particular in the early morning, due to accumulation of particulate matter under light wind conditions", according to NEA's weather forecast for April 16-30.