Singapore has experienced persistently poor air quality in its central region since early September, with pollutant levels reaching unhealthy thresholds amid ongoing haze conditions. Since September 4, the central area has consistently recorded the highest Pollutant Standards Index (PSI) and fine particulate matter (PM2.5) concentrations compared to the city-state’s other regions.
The PSI, a composite measure tracking air pollution, surpasses 100 during unhealthy air quality episodes. On September 15, the central region’s PSI peaked at 154 at dawn, while other zones ranged from 104 to 128. By late afternoon, the central PSI fell slightly to 133, with the east and west remaining in unhealthy ranges, and the north and south registering moderate levels of 92 and 94, respectively.
The National Environment Agency (NEA) identifies the central region to include areas such as Thomson, Marymount, Sin Ming, Ang Mo Kio, Bishan, Serangoon Gardens, MacRitchie, and Toa Payoh. Experts attribute the elevated pollutant levels in this area to urban characteristics. Koh Tieh Yong, an adjunct associate professor specializing in meteorology and climate science at the National University of Singapore, explained that dense urban infrastructure generates heat from concrete and buildings, causing rising warm air and increased turbulence. This turbulent air traps fine particulate matter carried by winds from Indonesian forest fires, concentrating pollutants near ground level in the central region.
Steve Yim, professor and director of the Centre for Climate Change and Environmental Health at Nanyang Technological University, noted that dry weather conditions in Singapore also contribute, as local emissions mix with haze particles to elevate pollutant concentrations, especially in downtown areas.
On September 15, all parts of Singapore recorded unhealthy PSI levels for the first time since 2009, illustrating the haze’s nationwide impact under thicker smog conditions.
The NEA clarified differences between Singapore’s PSI and other international air quality indices. While the PSI references the United States Environmental Protection Agency’s Air Quality Index (AQI) system, it is computed using six pollutants—PM10, PM2.5, sulfur dioxide, nitrogen dioxide, ozone, and carbon monoxide—and is tailored to local conditions. The agency emphasized that other platforms, including international websites and commercial sensor networks, use different methodologies and data sources, leading to variations in reported air quality figures.
Singapore’s PSI values are derived from highly specialized pollution analysers strategically located across its five regions. These devices employ internationally recognized methods to continuously monitor pollutant levels, ensuring reliable and scientifically robust data.
Residents are advised to limit prolonged or strenuous outdoor activities, particularly vulnerable groups with chronic heart and lung conditions, as haze persists. The ongoing haze situation underscores the challenges Singapore faces amid seasonal transboundary pollution exacerbated by regional forest fires and urban environmental factors.