Singapore is scheduled to incorporate PM2.5 into the current Pollutant Standards Index (PSI) as its sixth pollutant parameter since April 1, the city-state's Ministry of the Environment and Water Resources and the National Environment Agency (NEA) jointly said on Thursday.

The new index was firstly announced earlier this month when it was planned to come into force by May. The government then decided to bring forward the implementation of the new air quality reporting system "in view of the earlier onset of hazy conditions this year."

Environment and Water Resources Minister Vivian Balakrishnan said in a briefing on Thursday that the country may encounter worse haze than last June, when Singapore experienced its worst haze in history, with PSI recorded over 400.

Singapore experienced relatively high level of haze earlier this month as the region suffered a prolonged dry spell. Although the condition has been improved by the rain these days, Balakrishnan viewed the improvement as a temporary relief.

The authority said northeast monsoon has so far kept haze from Indonesia's Riau away from Singapore. However, during the coming inter-monsoon season, winds are light and may carry haze to Singapore if hotspots persist in central Sumatra.

Then the southwest monsoon will begin around June and could blow haze in Singapore's direction.

The authority also added that most climate models are projecting that an El Nino will develop in the second half of 2014.

A dry, El Nino year in the region "is usually associated with aggravated haze", local paper the Straits Times quoted Balakrishnan as saying.

Singapore now uses old PSI system with five parameters including PM10. Separately, the level of PM2.5 was firstly published by the government since 2012.