NEA: 'Unhealthy' PSI level in northern S'pore on Feb. 27 not due to forest fires in the region

Hot day.

Zhangxin Zheng | March 01, 2021, 01:02 AM

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The National Environment Agency (NEA) has confirmed that the sudden spike in Pollutant Standards Index (PSI) reported on Feb. 27 evening was due to heightened levels of ozone, possibly a spike in the formation of ground-level ozone.

'Unhealthy' 24-hour PSI level not due to fires in the region

In response to Mothership's query, NEA said that the PSI in the North region of Singapore entered the Unhealthy range due to heightened levels of ozone.

The ozone sub-index of the PSI is based on an average of ozone levels of the past eight hours.

NEA explained that weather conditions could be the reason behind the spike in PSI level on Saturday between 7pm and 8pm.

Maximum temperature in northern Singapore hit 35.3°C

The pollutants which contribute to the formation of ozone, such as nitrogen dioxide (NO2) and volatile organic compounds (VOCs), were within normal levels.

However, weather conditions such as ambient temperature, UV levels, wind speed, wind direction and rainfall can also influence the formation of ground-level ozone, NEA added.

NEA shared that the maximum ambient temperature in the North on Feb. 27 was 35.3°C. This was the highest recorded in 2021 for the North region.

This coupled with the high UV levels could have contributed to the elevated ozone levels reaching the 'Unhealthy' range, NEA said.

The PSI level returned to the Moderate range at 10pm.

The PSI last entered the Unhealthy range in 2019, from Nov. 13 to Nov.14, for eight hours in the South region, due to elevated PM2.5 levels.

Top photo by Zheng Zhangxin