Singapore’s Air Pollution and Its Implications

Air pollution in Singapore is measured locally by the country’s Pollutant Standards Index (PSI). The index is devised to provide a qualifiable measurement for air quality reporting. According to Singapore’s National Environment Agency, Singapore’s PSI measures six air pollutants, including Sulphur dioxide (SO2), particulate matter (PM10), fine particulate matter (PM2.5), nitrogen dioxide (NO2), carbon monoxide (CO) and ozone (O3). The PSI categorizes air quality into several tiers: PSI value in the range of 0–50 signifies a good air quality, PSI value in the range of 51–100 signifies a moderate air quality, PSI value in the range of 101–200 signifies an unhealthy air quality, 201–300 means very unhealthy and a value greater than 300 shows that the air quality is hazardous. This categorization is similar to that of Malaysia’s Air Pollution Index (API).

For most of the time, the PSI across the north, south, east, west, and central region of Singapore has been well below 100 and mostly fluctuating around 50, implying that Singapore has been able to manage its air quality island-wide. However, we do observe that there are several spikes in the past, during September and October 2014, September 2015, August 2016, March 2017, and Sept 2019. The increase in PSI is concentrated during the third quarter of the year, commonly during the outbreak of the Southeast Asian Haze. After 2014, the highest PSI reading recorded is 471 in October 2015. Since Singapore’s territory is rather small, pollutants tend to spread quickly and we are not able to see any significant differences in air quality between different regions.

Although Singapore’s air quality has been in the range of good to moderate for the past few years, there still lies the threat of the occasional unhealthy and hazardous air quality that is usually not caused by local reasons. The commonly cited reason for the third quarter air pollution spike is the transboundary haze caused by the forest fire in Indonesia. There has been evidence suggesting that exposure to the Southeast Asian Haze correlates with acute psychological, respiratory, cardiovascular, and neurological morbidity and even mortality. Although there is an increased risk of short-term respiratory morbidity during seasonal haze exposure, the long-term health outcomes are still unclear. The most common short-term symptoms include sore throat, dry mouth, nose discomfort, eye discomfort, headache, shortness of breath and skin irritation.[1] In particular, when the PM10 concentration increased by 200% during the 1997 haze, there was a 12% increase in upper respiratory tract illness cases and a 26% increase in rhinitis cases.[2] The emergency department visits and hospital admissions for respiratory conditions also increased significantly for every 30-unit increase in PSI.[3] In terms of out-of-hospital cardiac arrest (OHCA) incidence, Ho et al. found that unhealthy and even moderate levels of PSI are associated with increased OHCA occurrence, which is most significant among the population of age > 65 male, Indian, and non-traumatic. They also reported that when the PSI increased on the same day and the previous 1–5days by 30 units, it is associated with a 5.8–8.1% increased risk of OHCA.[4] Besides respiratory diseases, exposure to high levels of PSI has been associated with the disease of other organs. There have been suggestions that some pollutants may contain vasoactive properties when inhaled, affecting the blood vessels of those who have inhaled them.[5]

Although there is extensive research on the relationship between air pollution levels and health implications, most studies are based on Singapore’s PSI, which is not a universal tool and therefore making it difficult to conduct cross-country comparison. In addition, most studies on this topic are conducted based on Singapore’s dataset. Due to the nature of their studies, it is difficult for us to extrapolate the relationship found among residents of other countries in the region. But for now, we can only glimpse into the potential threat of haze exposure within Singapore.

[1] Cheong K.H., Ngiam N.J., Morgan G.G., Pek P.P., Tan B.Y-Q, Lai J.W., Koh J.M., Ong M.E.H., Ho A.F.W. Acute Health Impacts of the Southeast Asian Transboundary Haze Problem — A Review. International Journal of Environmental Research and Public Health. 2019; 16(18):3286. https://doi.org/10.3390/ijerph16183286

[2] Emmanuel, S.C., 2000. Impact to lung health of haze from forest fires: the Singapore experience. Respirology, 5(2), pp.175–182.

[3] Chan S.L., Ho A.F., Ding H., Liu N., Earnest A., Koh M.S., Chuah J.S., Lau Z.Y., Tan K.B., Zheng H., Morgan G.G., Ong M.E.. Impact of Air Pollution and Trans-Boundary Haze on Nation-Wide Emergency Department Visits and Hospital Admissions in Singapore. Ann Acad Med Singap. 2020 Feb;49(2):78–87. PMID: 32246709.

[4] Ho A.F.W., Wah W., Earnest A., Lam S.S.W., Ong M.E.H., Health impacts of the Southeast Asian haze problem — A time-stratified case crossover study of the relationship between ambient air pollution and sudden cardiac deaths in Singapore. International Journal of Cardiology. 2018; 271:352–358. https://doi.org/10.1016/j.ijcard.2018.04.070

[5] Tan, B.Y., Leong, A.Z., Leow, A.S., Ngiam, N.J., Ng, B.S., Sharma, M., Yeo, L.L., Seow, P.A., Hong, C.S., Chee, Y.H. and Chen, J., 2019. Psychosomatic symptoms during South East Asian haze crisis are related to changes in cerebral hemodynamics. PloS one, 14(1), p.e0208724.