Singapore haze: Air quality very unhealthy in central region; PM2.5 readings elevated across country

Singapore's air quality deteriorated overnight as haze spread across the island. The central region entered the very unhealthy PSI category at midnight on Friday. By 7am, its 24-hour PSI had reached 224, a new high for the year. This matters because pollution was not limited to one neighbourhood.

The rest of Singapore recorded unhealthy 24-hour PSI readings, ranging from 146 to 195. Hourly PM2.5 readings were also in the elevated band across all five regions. They ranged from 93 to 149. These figures show that both longer-term pollution levels and short-term particle levels were high.

The situation was worsening after a 24-hour PSI peak of 212 in the west on Thursday. The government began distributing N95 masks early because hourly PM2.5 readings were expected to keep spiking. Haze shelters were also opened at community clubs and selected community centres.

The PSI is a numerical index used to describe overall air quality over a stated period. In this article, the 24-hour PSI summarises pollution levels across the previous 24 hours. PM2.5 refers to fine particles small enough to be inhaled deeply into the lungs. It is a pollutant measurement, not an overall index.

The measures also use different time periods and purposes. PSI communicates the broader health significance of air pollution. PM2.5 reports the concentration of fine particles at a particular hour. The article records hourly PM2.5 readings from 93 to 149, while the central region's 24-hour PSI reached 224.

This distinction helps explain why a short-term spike can later raise the 24-hour PSI. On Wednesday, western Singapore's hourly PM2.5 peaked at 288. The article does not provide the PSI formula, but it shows how sustained or repeated particle pollution can worsen the wider air-quality reading.

A 24-hour PSI reading of 224 falls in the very unhealthy range. That means the pollution level was serious enough for Singapore's Haze Task Force to trigger N95 mask distribution for more vulnerable people. It also shows that high pollution persisted across many hours, rather than being only a brief spike.

The 2015 episode was more extreme by the particle measurement reported. During severe haze in October 2015, western Singapore recorded an hourly PM2.5 reading of 471 at 11pm on October 19. In the current episode, western hourly PM2.5 peaked at 288, the highest there since 2015.

These figures are not directly equivalent. The current figure of 224 is a 24-hour PSI, while 471 and 288 are hourly PM2.5 readings. Still, the comparison shows that current conditions were severe, although below Singapore's highest publicly logged hourly PM2.5 reading.

PM2.5 consists of very small particles that can travel deep into the respiratory system. Elevated exposure can irritate the eyes, nose, throat and lungs. It can also worsen asthma and other respiratory or heart conditions. These effects matter most when pollution is widespread or lasts for many hours.

Children, older adults, pregnant people and those with existing lung or heart disease are generally considered more vulnerable. This is established health guidance; the article itself does not specify which groups are included. It does report that N95 masks would be distributed to more vulnerable individuals when the 24-hour PSI exceeded 200.

Singapore acted before the situation worsened further. Grace Fu said distribution began early because one-hour PM2.5 readings were likely to keep spiking. Haze shelters were also established. These measures reduce exposure, but the article does not report particular illnesses or hospital numbers from this episode.

Forest and peatland fires in Indonesia are the reported source of the worsening haze. Smoke from large fires can spread beyond the country where burning occurs when winds carry it across borders. This matters because Singapore can experience unhealthy air even though the fires are elsewhere.

The article directly links the Indonesian fires to Singapore's worsening haze, but it does not describe wind direction, fire locations or the exact transport path. The key mechanism is cross-border movement of smoke, which contains fine particles such as PM2.5. Those particles contributed to elevated readings in all five Singapore regions.

Prime Minister Lawrence Wong said Singapore was investigating which companies might be responsible for the fires. Where warranted, Singapore will consider action under its Transboundary Haze Pollution Act and explore joint action with other countries. The article does not say whether any company has yet been identified or prosecuted.

Singapore distributed N95 masks and opened haze shelters because air pollution had reached very unhealthy levels. The Haze Task Force had planned distribution when the 24-hour PSI exceeded 200. The government brought it forward after western hourly PM2.5 entered the very high band and forecasts suggested more spikes.

An N95 mask is designed to filter very small airborne particles. Its protection depends on a close fit around the face, because gaps allow polluted air to enter. Shelters offer an alternative indoor location during the haze. The article names community clubs and selected Residents' Committee and Residents' Network centres as shelter sites.

Distribution began in phases at community clubs, vending machines and People's Association venues. NEA warned that supplies might not be immediately available everywhere, but said government stockpiles and retailers' warehouses had sufficient stocks. People were told to check availability before visiting collection points.

Peatlands contain deep layers of partly decomposed organic material. When they dry and catch fire, the peat can smoulder below the surface instead of burning only in visible flames. This makes the fire difficult to detect and extinguish. The article identifies Indonesian peatland fires as a source of Singapore's worsening haze, but does not explain their behaviour.

Because underground peat can keep smouldering, it may release smoke over an extended period. Wind can then carry that smoke across national borders. Fine particles in the smoke can raise PM2.5 readings far from the fire. These are established properties of peat fires and explain how burning in Indonesia can affect Singapore.

The current consequences were clear: central Singapore's 24-hour PSI reached 224, while all five regions recorded elevated hourly PM2.5. Singapore is investigating possible corporate responsibility and considering action under its haze law. Longer-lasting fires would increase the need for masks, shelters and monitoring.