Wind direction key to good, bad and hazardous air

SINGAPORE - Breathing will be a breeze - if the breeze is blowing in the right direction.

With Singapore still under threat of a return to hazardous conditions, and rain still scarce over the burning fields of Sumatra, the answer, it seems, is blowing in the wind.

It was the wind that blew the haze away from our shores, resulting in the improvement you've experienced since Saturday afternoon. This, despite there being more burning in Riau.

The three-hour PSI at 11pm yesterday was 61, a far cry from the record 401 of last Friday afternoon.

"The haze was blown away from us," said weather services director Patricia Ee of the Meteorological Services at a daily technical briefing yesterday."

For the next few days, dry weather conditions and the prevailing southerly to south-easterly winds are expected to continue.

Slightly hazy conditions can be expected.

Said chairman of the Haze Inter-Ministerial Committee Ng Eng Hen at a briefing at Changi Airport: "Singapore was blessed over the weekend. Our chief meteorologist told us that the wind shifted suddenly, blowing the haze northwards. Muar and KL were hit, and we empathise with the Malaysians. But the haze could return anytime and we must be prepared when it does."

Dr Erik Velasco, who studies air pollution at the Singapore-MIT Alliance for Research and Technology, said a change of 15-20 degrees in the wind direction would cause the haze to miss Singapore.

The improving air quality occurred despite the growing number of hot spots - a total of 437 were observed yesterday, said the National Environment Agency (NEA), compared with 173 last Wednesday.

Muar's grief

But Singapore's relief was Muar's grief. The Malaysian town's Air Pollutant Index (API), Malaysia's measure of air quality, reached a high of 746 on Sunday morning. But it seems the winds are changing for them, too.

On Monday, Muar's API dipped from hazardous levels to an unhealthy level of 125 at 5pm.

Will the air quality in Singapore reach Muar's API of 746?

It's possible, said Dr Velasco. "We reached PSI 401 last Friday at 1pm, and no one thought we would reach that level. It all depends on three factors: Intensity of the fires, wind direction and boundary layer."

The boundary layer refers to the air layer near the ground.

Malaysia and Singapore use the US Environmental Protection Agency standard, which measures only up to a scale of 500.

Muar's API reading of 746 is based on a linear extrapolation beyond the hazardous range which is unscientific, said project director of NEA's Pollution Control Development Indrani Rajaram. The maximum reading of 500 on the PSI comes to about 577 on the API.

The API is identical to PSI during the haze period, when the pollutant with the highest concentration is PM10.

linheng@sph.com.sg


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