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SINGAPORE – Air quality returned to unhealthy levels in northern parts of Singapore on Sunday night (March 28) due to high ozone concentrations, according to the National Environment Agency (NEA) website. ).
At 8 p.m., the Pollutant Standards Index (PSI) reading stood at 114, in the unhealthy range, though it returned to the moderate range at 9 p.m., with the PSI dropping to 97.
Air quality is considered unhealthy when the PSI is in the range of 101 to 200. Under these conditions, healthy people are urged to reduce prolonged or strenuous physical exertion outdoors, while vulnerable groups, including the elderly , should minimize prolonged physical activity.
When the PSI is above 200, it is in a very unhealthy range.
PSI is calculated based on six pollutants: particulate matter, fine particulate matter (PM2.5), sulfur dioxide, carbon monoxide, ozone, and nitrogen dioxide.
This means that an increase in the concentrations of any of the six can lead to deterioration in air quality.
As of 9 p.m. Sunday, the eight-hour average ozone concentration was above 100 in Singapore’s northern, central and southern regions, according to the NEA website.
During periods of fog caused by forest fires in the region, the dominant pollutant is PM2.5.
On Sunday, the hourly concentration of fine particles remained in the normal range. The 24-hour average of the PM2.5 readings was within the moderate range.
Similar conditions had been reported on February 27, when PSI levels had entered an unhealthy range.
A NEA spokesperson told The Straits Times on March 2 that pollutants that contribute to ozone formation, such as nitrogen dioxide and volatile organic compounds, were within normal levels.
However, climatic conditions such as ambient temperature, ultraviolet levels, wind speed, wind direction, and rainfall can also influence ozone formation at ground level.
For example, the maximum temperature on February 27 was 35.3 degrees Celsius. This was the highest recorded in 2021 for the northern region, the spokesperson said.
Along with the high ultraviolet levels, this could have contributed to the elevated ozone levels, reaching an unhealthy range, he added.
ST has contacted NEA again for comment.
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