Indoor air quality can exceed outdoor levels as Singapore endures prolonged haze
Tests in Singapore homes show PM2.5 concentrations can be higher indoors than outside, while air purifiers lower levels more effectively than air-conditioners and some expired N95 masks still meet filtration standards.
A recent test in a fifth-floor Singapore flat found a PM2.5 concentration of 187 µg/m³ after the windows were closed for an hour, higher than the outdoor reading of 169 µg/m³. Similar measurements in a 15th-floor unit recorded 149 µg/m³ indoors, which rose to 301 µg/m³ when the windows were opened as haze intensified.
“If the air quality is poor outside, it’ll be poor inside as well,” said Leonard Ng, an assistant professor at Nanyang Technological University, who conducted the measurements with a professional-grade monitor.
Ng advised that windows should only be opened when outdoor PM2.5 levels are moderate. Running an air-conditioner for ten minutes reduced indoor PM2.5 from 131.6 to 109.8 µg/m³, still within the elevated range, whereas operating an air purifier for an hour lowered the reading to 40.7 µg/m³, entering the normal band. He recommended selecting purifiers based on clean-air delivery rate and using filters rated for PM2.5 removal.
ST Engineering tested two N95 masks that expired in 2017 and found they filtered 99 % of test particles, exceeding the 95 % requirement. A mask that expired in 2022 performed at 93 %. Jerome Lee, head of respiratory protection at ST Engineering, explained that some manufacturers design masks with a safety margin and that storage in cool, dry conditions can preserve performance, but warned that degradation cannot be seen visually and that damaged masks should be discarded.
Comparisons of air-quality data showed discrepancies between Singapore’s National Environment Agency (NEA) website and third-party platforms such as the World Air Quality Index. Natasha Jamali, principal scientific officer at NEA, said differences arise from varied data sources, sensor calibration, and distinct calculation methods used by the United States Environmental Protection Agency versus Singapore’s own formula.
Exercise outdoors during the haze increases inhaled PM2.5. A cardiopulmonary test indicated that moderate activity can triple breathing rates, while maximal effort may raise them sixfold. Senior consultant cardiologist Peter Ting noted that vigorous exercise could lead to inhaling 10–20 times more air than at rest, raising cardiovascular risk. He advised checking the one-hour PM2.5 reading, reducing workout intensity and duration, and avoiding busy roads.
NTU climate researcher Wang Jingyu projected that the northeast monsoon could bring relief by mid-November, though a secondary haze season may occur from March to May. He also warned that future climate patterns may become more El Niño-like, potentially increasing regional fire risk. The Association of Southeast Asian Nations has a roadmap targeting a haze-free region by 2030, and recent enforcement actions under the Transboundary Haze Pollution Act have been taken against companies in Indonesia and Singapore.