Singapore is currently experiencing its longest period of unhealthy air quality since last September, with the Pollutant Standards Index (PSI) registering levels above 101 consistently since October 5. Authorities have cautioned that conditions could deteriorate further, potentially reaching "very unhealthy" levels if the persistently hot and hazy weather continues.

Pollution during this period is dominated by fine particulate matter known as PM2.5, which consists of particles measuring 2.5 microns or smaller—approximately 30 times thinner than a human hair. These particles are capable of penetrating deep into the lungs and entering the bloodstream, posing health risks.

Experts have clarified that while air conditioners provide relief by cooling indoor environments, their standard filters are typically designed to capture larger dust particles rather than the much smaller PM2.5 pollutants associated with haze. Liu Zheng from the Nanyang Technological University’s School of Materials Science and Engineering explained that typical air-conditioners largely recirculate indoor air and their filters do not efficiently remove fine haze particles. However, using air conditioning can indirectly reduce indoor haze levels by encouraging occupants to keep doors and windows closed.

Rajasekhar Balasubramaniam from the National University of Singapore’s College of Design and Engineering noted that household air-conditioning units generally lack filters capable of capturing fine particulate matter effectively. Upgrading to filters with a Minimum Efficiency Reporting Value (MERV) rating of 13 or higher can improve filtration. Meanwhile, air purifiers equipped with High-Efficiency Particulate Air (HEPA) filters are better suited for removing fine particles when used in enclosed spaces, provided the device’s capacity matches the room size. Philip Eng, a senior consultant respiratory physician at Mount Elizabeth Hospital, emphasized that HEPA filters must not be confused with humidifiers or dehumidifiers, which serve different functions.

Regarding indoor plants, Singapore Environment Council executive director Cheang Kok Chung and Balasubramaniam both indicated that while plants can absorb certain gaseous pollutants like volatile organic compounds, they are largely ineffective at removing PM2.5 particles due to their limited surface area and contact with indoor air.

The National Environment Agency uses two primary indicators to report air quality: the 24-hour PSI and one-hour PM2.5 readings. The PSI reflects an aggregate measure of six pollutants—PM10, PM2.5, sulfur dioxide, nitrogen dioxide, ozone, and carbon monoxide—and is averaged over a 24-hour period, which may sometimes mask short-term fluctuations in haze conditions. Recently, the PSI reached a high of 192 in the central region on October 9 between 5 p.m. and 8 p.m., while the highest hourly PM2.5 reading for 2026—171—was recorded in the western part of Singapore at 2 a.m. that same day.

In response to the haze, the government announced plans to distribute N95 masks to vulnerable groups and individuals with limited resources when air quality reaches "very unhealthy" levels. Mask vending machines will also be installed at selected public transport hubs and social service offices to support distribution efforts carried out by grassroots organizations. Officials have assured that there is an ample supply of N95 masks in retailers’ warehouses and government stockpiles, and that coordination with retailers is ongoing to maintain availability for the public.