Quantifying Air Quality – The Pollutant Standards Index (PSI)


Most Developed Countries (DCs) regulate environmental standards by putting caps on the emissions of criteria pollutants that empirical evidence has shown to be harmful to human health1. The PSI is one way to quantify air quality and has been adopted by Singapore to be the authoritative indicator of air quality in the country. Once quantified, it also aids in informing the public about the risks posed by different levels of air quality by affixing health advisories to each level.

Since 2013, every incident of transboundary haze brings with it a period during which the PSI becomes an oft-cited figure amongst ordinary Singaporeans in our daily lives. It seems as if when communicating about air quality with one another, merely saying that air quality is unfavourable would be unsatisfactory. A means by which we can put a number to air quality gives people a sense of scale as well as benchmarks for comparison as air quality usually varies as often as throughout the course of a day.

How is the PSI calculated?

The concentration of each criteria pollutant is compared to a standard index which is used to determine the sub-index assigned to the most recent recording of the concentration of the pollutant in question. The highest sub-index, whichever criteria pollutant that may represent, is taken as the PSI level2.

The PSI, as it was calculated before April 2014, took into account five criteria air pollutants. These were SO2, nitrous oxides, CO, PM10, and O3. The inclusion of PM2.5 occurred in 20142 when the National Environment Agency was of the opinion that a greater focus on PM2.5 was necessary to better reflect reality on the ground in the air as PM2.5 are finer particles that pose a higher threat to human respiratory health as compared to the more generalized pollutant known to us as PM10.

Was the inclusion of PM2.5 as a criteria pollutant in April 2014 necessary?

Velasco and Rastan (2015)3 of the Singapore-MIT Alliance for Research and Technology and the National University of Singapore respectively, certainly seem to think so. A paper published by the pair in 2015 noted that “the real hourly pollution levels” during the haze incident that year had still been unrecorded. This was in no small part attributable to the fact that before 2014, the only indication of PM2.5 in the atmosphere was the PM10 reading. This was in spite of the fact that during the episode, it was shown that the reported PM10 levels had been an under-representation of the significantly poor quality of air that existed in reality at the time. The methodology undertaken by Velasco and Rastan was to use newly collected information on PM2.5 concentrations since April 2014 and derive statistical models by which they could predict with an insignificant degree of uncertainty the actual hourly PM2.5 during the episode in mid-2013. Their findings indicate that these values could very well have been “twice the maximum 24-hour moving average reported by the authorities.”3

The findings of Velasco and Rastan seem to provide credence to the notion that incorporating PM2.5 as a new criteria pollutant measured by the PSI was a good move on the part of the local authorities. While it seems intuitive that more needs to be done to overcome the problem of the lag time in the official PSI readings published by NEA, refining the methods of measurement of the PSI seems to be a step in the right direction.


[1] Hamilton, S.F. & Requate, T. (2012). Emissions standards and ambient environmental quality standards with stochastic environmental services. Journal of Environmental Economics and Management, 64, 377-389. Retrieved from http://ac.els-cdn.com/S0095069612000538/1-s2.0-S0095069612000538-main.pdf?_tid=694d5626-7df9-11e5-ae0e-00000aacb35f&acdnat=1446094767_6ae8a0a14e35f289d579711c6397edb6.

[2] National Environment Agency. (2015). PSI. [Online]. Retrieved from http://www.nea.gov.sg/anti-pollution-radiation-protection/air-pollution-control/psi/psi.

[3] Velasco, E. & Rastan, S. (2015). Air quality in Singapore during the 2013 smoke-haze episode over the Strait of Malacca: Lessons learned. Sustainable Cities and Society, 17, 122-131. Retrieved from http://ac.els-cdn.com/S2210670715000463/1-s2.0-S2210670715000463-main.pdf?_tid=fd72d6f8-7dfb-11e5-b248-00000aab0f26&acdnat=1446095874_7c02d98301a4465fb7cb71472bc5fa0a.

Transboundary Haze – Care To Air Your Views?

Dr Haridas
Ms Lee Li Lian

The haze affects different people in different ways. But there are things we can do to make life a bit better for those around us and ourselves as well.

My aunt, Dr Haridas, whilst keenly aware of the health hazards posed by the haze and that she has to look out for patients showing symptoms of haze-related health issues, also knows she has to exercise due diligence by not assuming that every patient who reports irritation to his or her eyes, for instance, is not suffering as such due to the haze alone.

Ms Lee Li Lian, using her voice and influence as my Member of Parliament, had tabled a Parliamentary Question in 2013 to ask the Minister for Health “(a) what effort has been made to make parents more aware of the advice that N95 masks are not designed for children; and (b) whether the Government intends to make available masks that are certified for children in public health emergencies.” 1Today, she continues her efforts to help the local community in various ways, having distributed masks to residents at a grassroots event recently.

My young friend and neighbour, Beckham plays his own part as well by reminding his secondary school friends on Facebook to wear masks when leaving the house.

And last but by no means least, my best friend Tirta whilst feeling sympathetic towards his fellow countrymen who have little choice but to bear the worst consequences of the haze, also recognises that this is a problem that not only doctors, politicians and those more vulnerable to the effects of the haze should be worried about – it is a problem that speaks to all of us, young or old, with urgency regardless of how seemingly helpless ordinary folk like us may perceive ourselves to be.


[1] Parliament of Singapore. (2013). Safeguarding Singaporeans’ Health During Occurrence of Haze. Official Reports -Parliamentary Debates (Hansard), 90, Sitting 19. Retrieved from http://sprs.parl.gov.sg/search/topic.jsp?currentTopicID=00000151-WA&currentPubID=00000140-WA&topicKey=00000140-WA.00000151-WA_2%2Bid-43fcd59a-3ee3-45fa-a762-817fde5e1d55%2B4.

Photo Credits:

IMG: Ms Lee Li Lian – Punggol East Constituency Committee

IMG: Beckham – Beckham Song Ying

The Transboundary Haze Pollution Act: What It Can and Cannot Do.


The Transboundary Haze Pollution Act was introduced to Parliament on 7th July 2014. It was debated by the House on 4th August 2014, committed to a Committee of the Whole House and passed after its Third Reading a day later on 5th August 20141. The Act came into effect on 25th September 20142.

The introduction of the Bill to the House came a year after Singapore suffered its worst incidence of air pollution caused by haze, with the highest recorded PSI levels the country had ever experienced3. In his opening speech to the House on the occasion of the Second Reading of the Bill4, then Minister for the Environment and Water Resources, Dr Vivian Balakrishnan, noted that the a legislative approach to Singapore’s response to the haze was necessitated not so much by Indonesia’s lack of environmental laws as by their lack of ability in enforcing these laws.

Part II of the Act sets out commercial or other entities’ liabilities for transboundary air pollution5. The provisions contained therein make it an offence for entities to be involved in causing haze. The law extends the scope of entities or companies covered under the Act to include those that may not be directly causing haze but are in some way involved in the management of another entity or company that owns land and contributes to causing haze from there. Furthermore, the legislation also specifies that it shall be a statutory duty of such companies to ensure compliance. Entities that have been found to have acted in contravention of the Act are also liable to provide compensation if there is evidence that the haze caused by them has affected any “person, property or the environment” in Singapore.

A key feature of the Act is the extraterritorial nature of the extent and reach of the legislation. The Act applies not only to companies based within Singapore but also to foreign-owned ones. Minister Balakrishnan assured the House that, “This exercise of extra-territorial jurisdiction under this Bill is in line with international law, specifically the objective territorial principle.” However, the effectiveness of the extraterritoriality of the Act is questionable. Then Non-Constituency Member of Parliament, Mr Yee Jenn Jong of the Workers’ Party, rose to point out6 that Singapore has no extradition treaty with Indonesia and that, “If the accused person fails to appear in court, a warrant of arrest is issued under Section 17. This will likely have little or no effect if the person is not in Singapore.”

Other practical constraints limit the effectiveness of the Act. In order to prosecute perpetrators, the Government of Singapore would have to be able to accurately identify them according to the lands on which forest fires were started and spread to. However, this can only be done if Indonesia agrees to share cartographic information with Singapore. Even if the Indonesian authorities agreed to do so, the prevailing complexity of forested land tenure issues in Indonesia would render it onerous to distinguish the rightful owners of the land in question from commercial perpetrators if indeed such distinctions can and ought to be made in the first place. This was a point raised by the then Nominated Member of Parliament, Ms Faizah Jamal, who represented environmental interests in the House.

During the debate on the Bill, MPs from all sides of the House recognised that the key to solving the woes of transboundary haze lies beyond a legislative approach. Member of Parliament for Marine Parade, Associate Professor Fatimah Lateef said, “Education must continue. Commitment must be inculcated. Mutual trust must continue to be strengthened.” Mr Yee of the Workers’ Party urged the Government to not only look at how forest fires can be prevented but to extend our diplomatic efforts to helping Indonesia develop “a more sustainable agro-industry.” The most sobering view, however, came from Ms Jamal, who proclaimed that the Government has to take the lead in changing our approach to the bigger picture of consumerism for the better. She said, “The ordinary citizen as consumers should be made aware that they have the power to change a business model that has thus far been more concerned about profits than about people or planet, provided citizens start by taking back responsibility for their own part in the problem. It is no use playing the blame game when there is no sense of personal responsibility for the consumer choices that we make individually and collectively as a country.” Today, with the greying of our skies once again, local companies took to improving their consumption practices with much support from the public.

Two things are certain. From an environmentalist’s perspective, it should not have to take a bad bout of haze for us to improve the way we use the environment. And, from a political and legal perspective, it will not take a single Act of Parliament alone to prevent these bouts from recurring to colour our skies grey once again.

[1] Parliament of Singapore. (2014). Bills Introduced. Singapore: Parliament of Singapore. Retrieved from http://www.parliament.gov.sg/publications/bills-introduced.

[2] National Environment Agency. (2014). Parliament Statements. Singapore: Government of Singapore. Retrieved from http://www.nea.gov.sg/corporate-functions/newsroom/parliament.

[3] Velasco, E. & Rastan, S. (2015). Air quality in Singapore during the 2013 smoke-haze episode over the Strait of Malacca: Lessons learned. Sustainable Cities and Society, 17, 122-131.

[4] Parliament of Singapore. (2014). Transboundary Haze Pollution Bill. Official Reports -Parliamentary Debates (Hansard), 92, Sitting 10. Retrieved from http://sprs.parl.gov.sg/search/topic.jsp?currentTopicID=00006470-WA&currentPubID=00006417-WA&topicKey=00006417-WA.00006470-WA_2%2Bid-2242cb2e-c3e5-4597-9bfa-bbaa6c57a231%2B.

[5] Transboundary Haze Pollution Act 2014 (Act 24 of 2014).

[6] Parliament of Singapore. (2014). Transboundary Haze Pollution Bill. Official Reports -Parliamentary Debates (Hansard), 92, Sitting 11. Retrieved from http://sprs.parl.gov.sg/search/topic.jsp?currentTopicID=00006478-WA&currentPubID=00006482-WA&topicKey=00006482-WA.00006478-WA_1%2Bid-4067f594-ea00-4e20-ac4b-1ad5493c5b74%2B.

Clearing the Air on the Haze – A Hazy New Year?


“As any geographer would attest to, the haze itself might be dull in sight, but insight into the haze is surely never boring.”

The Straits Times reported on October 19th 2015 that the haze could persist until 20161. A researcher from the Centre for International Forestry Research was quoted as saying that it might very well last until the final month of 2015 or the first month of next year. Unsurprisingly, many Singaporeans might wonder why we are to bear the brunt of the haze for a longer period than our squeaky clean and ‘sterile’ respiratory airways are normally accustomed to. Amongst the reasons for the persistence of the haze are factors of a geographical nature.

The seasonal monsoons experienced in this part of the world that straddles the Equator are the main culprits. In June 2013, the worst haze in Singapore’s meteorological history was recorded. The southwest monsoon was the main cause of the haze as winds blowing from Sumatra to Singapore carried a comparatively higher concentration of particulate matter (PM) particles with them2. In March 2014, the haze was back again – but this time, the northeast monsoon was the primary cause of the public’s ire. Its northeasterly winds were retreating back northwards3, accompanying the gradually moving Inter-Tropical Convergence Zone (ITCZ) with the approach of warmer temperatures in the northern hemisphere. Now, in October 2015, however, one would expect a taming of the haze as the northeast monsoon comes to our rescue – to rid us of the prevailing southwesterly winds that have been carrying too many PM particles4 with frequencies greater than comfort ordinarily affords. However, in any given locality, the replacement of the southwest monsoon by the northeast monsoon during the inter-monsoon period is a gradual process5 that requires patience on the part of the people who would be expected to relish in this seasonal change.


Diagram 1: Sea Surface Temperature anomalies across the tropical Pacific (22nd October 2015) enable us to visualise the temperature disparities across the Pacific Ocean that drive the El Niño Southern Oscillation. Source: National Oceanic and Atmospheric Administration (NOAA), United States.

This time, however, hope for clearer skies might be further afield than initially expected due to the current cycle of the El Niño Southern Oscillation (ENSO) being experienced in our part of the world. The ENSO is brought about by cross-longitudinal changes in oceanic water circulation that results in a change in temperatures across oceans (Diagram 1). In the case of the eastern margins of the Pacific Ocean, warmer sea surface temperatures bring higher rainfall to South American countries such as Chile. The corollary to this is that Singapore and the rest of Southeast Asia that lie along the western margins of the Pacific Ocean experience drier conditions brought about by easterly winds rid of moisture6. The ENSO occurs every few years and lasts for variable periods of time7. Drier conditions that may exacerbate forest fires in Indonesia due to the persistence of the ENSO are the reason cited by geographers and meteorologists as to why the haze might continue up until January 2016. It is worth noting that this is certainly not the first time the ENSO and Indonesian forest fires made for a fearsome combination. In 1997, the ENSO brought about forest fires in Kalimantan, Indonesia that emitted a thick aerosol plume, forcing the shutting down of airports in Indonesia, Malaysia and Singapore.

There might exist a commonly held misconception in the Singaporean psyche – that our country does not experience seasonal changes in weather patterns. We do. There is also perhaps a feeling amongst those who are uninitiated with the geography of weather and climate that compared to life in temperate countries, living in Singapore makes for a boring existence due to the high year-round temperatures and rainfall experienced here where snow can only be artificially manufactured in air-conditioned enclosures and where tomorrow’s weather must surely be as mundane as that of any other day in the year. On the contrary, our susceptibility to seasonal weather patterns has impacts on our daily lives that are more real than one might imagine, given the right conditions (in this case, an anthropogenic condition imposed upon us by our neighbours which is being heightened in its effect by physical conditions). As any geographer would attest to, the haze itself might be dull in sight, but insight into the haze is surely never boring.


[1] The Straits Times. (2015). Hazy new year: South-east Asia set to suffer for months as Indonesia fails to douse fires. (2015, October 19). Retrieved from http://www.straitstimes.com/asia/se-asia/hazy-new-year-south-east-asia-set-to-suffer-for-months-as-indonesia-fails-to-douse.

[2] Velasco, E. & Rastan, S. (2015). Air quality in Singapore during the 2013 smoke-haze episode over the Strait of Malacca: Lessons learned. Sustainable Cities and Society, 17, 122-131.

[3] Meteorological Service Singapore. (2014). Update of Regional Weather and Smoke Haze for April 2014. Singapore: Government of Singapore. Retrieved from http://wip.weather.gov.sg/wip/pp/ssops/reparch/apr14.pdf.

[4] Ministry of Foreign Affairs. (2015). Press Statement: Singapore Registers Haze Concerns with Indonesia. (2015, September 10). Retrieved from http://www.mfa.gov.sg/content/mfa/overseasmission/jakarta/press_statements_speeches/2015/201509/Singapore_Registers_Haze_Concerns_With_Indonesia.html.

[5] ASEAN Specialised Meteorological Centre. (2015). Update of Regional Weather and Smoke Haze for September 2015. Singapore: Association of Southeast Asian Nations. Retrieved from http://asmc.asean.org/wp-content/uploads/2015/09/Sep15.pdf.

[6] Cane, M. (2005). The evolution of El Niño, past and future. Earth and Planetary Science Letters, 230, 227-240.

[7] Chen, D. & Cane, M.A. (2008). El Niño prediction and predictability. Journal of Computation Physics, 227, 3625-3640.