I think we’re all attuned to sniffing out the haze by this point.
And for the residents living in the north, you probably groaned when you smelt the all too familiar scent of something burning on Sunday (28 Mar).
The National Environment Agency (NEA) announced that the high concentration of ozone in the northern parts of Singapore was likely due to a combination of factors such as high ambient temperatures, light winds, and elevated ultraviolet (UV) levels during the day.
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The 24-hour Pollutant Standards Index (PSI) entered the unhealthy range (101-200) from 6:00pm to 8:00pm on Sunday.
At around 8:00pm, the PSI level stood at 114 before falling to 97 at 9:00pm.
The PSI is calculated based on six pollutants, namely, particulate matter, fine particulate matter (PM2.5), sulphur dioxide, carbon monoxide, ozone and nitrogen dioxide.
However, as the hourly concentration of PM2.5 was within the normal range on Sunday, it was the other pollutants that resulted in the deterioration in air quality.
People are urged to reduce prolonged or strenuous outdoor physical exertion when the PSI rises above 100, as ozone can irritate the linings of the respiratory passage.
One more excuse to not go for an evening run, aha!
Weather Conditions Contributed to the High Concentration of Ozone
Ozone is formed when components of the air, nitrogen oxides and volatile organic compounds react under specific environmental conditions, including the presence of sunlight.
However, as the nitrogen dioxide and volatile organic compounds were within normal levels on Sunday, NEA notes in response to The Straits Times that it was the wind and high temperatures which resulted in the high levels of ozone.
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An air pollution expert, Dr Erik Velasco, also chimed in that Singapore might be facing phytochemical pollution, with emissions coming from traffic or the use of solvents in households.
Associate Professor Koh Tieh Yong, a weather and climate scientist at the Singapore University of Social Sciences pointed out that the ozone sub-index contributed to the peak in the PSI measured in Woodlands and MacRitchie Reservoir.
The high temperatures of 32–34°C measured at Admiralty and Ang Mo Kio weather stations also allowed ozone to form rapidly, said Professor Koh.
Low humidity levels on Sunday also meant the air’s natural cleaning agents, known as hydroxyl radicals, were in low supply, preventing the quick removal of ozone.
This led to a high concentration of ozone in Woodlands, which was blown to MacRitchie Reservoir by the southward winds.
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Occurrences of high heat and low humidity are “not unusual” in the northern parts of Singapore as the region is the furthest away from the sea.
However, he reassured that there was no need to fear ozone exposure as its concentration would fall during the night, due to the lack of light to aid its production.
Feature Image: Tang Yan Song / Shutterstock.com (Image for illustration purpose only)
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