Clearer skies as F1 kicks off but hazy conditions to stay

The Formula 1 weekend revved off yesterday under relatively clear skies, although hazy conditions could persist at the weekend, said the weatherman.

At 10pm yesterday, the 24-hour Pollutant Standards Index (PSI), a measure of air quality, was in the moderate range across Singapore.

Favourable winds kept the pollution from fires in Indonesia at bay.

This is an improvement from the unhealthy air quality experienced here over the past week.

At a media briefing yesterday, the National Environment Agency (NEA) said it expects the 24-hour PSI at the weekend to be between the high end of the moderate range and low end of the unhealthy range.

The one-hour PM2.5 reading is forecast to fluctuate between the normal and elevated bands.

But in the coming days, the agency said, dry weather is expected to persist over south Sumatra - the origin of most of the haze that Singapore is experiencing.

If winds blow from that direction, the PSI could creep into the middle of the unhealthy range.

However, NEA said showers are expected in south Sumatra at the end of the month, and this could provide some respite.

After years of clear skies, Singapore and the rest of South-east Asia are once again plagued by haze.

Still, the situation is not yet as bad as it was in 2015, when the region suffered its worst haze episode on record.

That year, a climate phenomenon known as El Nino caused hotter and drier weather in South-east Asia, worsening the forest fires in In-donesia and causing them to spiral out of control.

El Nino conditions are not present this year in this part of the world, although the region is experiencing hotter and drier weather than usual.

This is due to a persistent cooling of sea surface temperatures in the eastern Indian Ocean, off the west coast of Sumatra, which hinders the formation of rain clouds.

However, it is not clear yet if this year's haze episode would be as bad as the 2015 crisis, NEA said.

The fire season started earlier that year, and there were more hot spots detected then, compared with current observations.

However, this year's fire season is not over yet. Determining whether the haze this year could be as bad as 2015 depends on multiple factors, including weather and the persistence of forest fires, NEA said.

During yesterday's briefing, NEA also cleared up some misconceptions over how it tabulates the 24-hour PSI.

Many had questioned whether the figures on NEA's website have downplayed the severity of the haze, and turned to other air quality readings, such as the World Air Quality Index, which is compiled by a non-profit organisation headquartered in Beijing.

NEA has since clarified that there are no international guidelines on how air quality indexes should be computed. "Countries adopt different index systems based on their local needs and circumstances," said a spokesman.

These include considerations such as how urban the setting is and what the surrounding industries are like. This is important as it takes into consideration the baseline air quality - or air quality during periods with no haze.

As this baseline differs from city to city, no two air quality indexes are alike, NEA clarified.

The NEA provides two air quality readings - the 24-hour PSI and the one-hour PM2.5 readings. Both serve different functions.

The one-hour PM2.5 measures the average hourly concentration of PM2.5 particles - the dominant pollutant during haze episodes - and is meant to help people gauge immediate activities, such as whether to go for a jog.

However, forecasts of the 24-hour PSI should be relied on when planning future activities, such as whether one should go for a picnic the next day. NEA said this forecast is made based on the current haze situation as well as its predictions of weather variables, such as wind direction or if rain is expected.

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