SINGAPORE - Good weather may have kept the haze away from Singapore for now, but it is unlikely that the seasonal plague is gone for good.
Plumes of smoke haze have clouded Singapore's skies almost every year from as far back as the 1960s, with the first haze episode reported on Oct 19, 1961.
We look back at 55 years of haze history:
1. When it all started
Singapore's first encounter with haze was on Oct 19, 1961.
The haze that day was so bad that an aircraft flying from London missed its destination, Kuala Lumpur, and overflew to Singapore. The Straits Times also reported then that several readers had called in to ask if the haze had anything to do with a nuclear fallout.
2. Introducing the PSI
In 1991, Singapore's Environment Ministry introduced the Pollutant Standards Index (PSI), which indicates the concentration of suspended particles, sulphur dioxide, nitrogen dioxide, carbon monoxide and ozone in the air.
As a recap, health advisories issued by the authorities are based only on the 24-hour PSI, which measures the average concentration levels of component pollutants over the past 24 hours. This is because scientific and epidemiological studies on the health effects of particulate matter have been based on 24-hour exposure, and not shorter-term measurements.
There are five air quality descriptors: Good, Moderate, Unhealthy, Very Unhealthy and Hazardous.
For more info on the types of activities that should be carried out during these periods, go to www.haze.gov.sg.
3. El Nino and haze
The year 1997 was an El Nino year, during which Indonesia experienced drier than usual conditions which made the peatland and forests there more flammable.
Fires in Sumatra and Kalimantan smothered the whole region in the worst haze at that time. The fires razed about 5 million ha of virgin forest and agricultural land in South Kalimantan and Sumatra, an area nearly 80 times the size of Singapore.
Considered one of the worst haze episodes to hit Singapore, it resulted in over $500 million in disruptions and lost revenue, according to environmental group World Wide Fund For Nature.
But that was not the worst haze crisis Singapore has encountered.
The most serious episode was in 2015, which was also an El Nino year.
4. The day when three-hour PSI hit 401
On June 21, 2013, the three-hour PSI climbed to 401, causing panic among some Singaporeans. Long queues formed at pharmacies and shops selling the N95 mask. But the authorities stopped short of issuing stop-work orders and asking schools to close as the 24-hour PSI did not reach hazardous levels.
But amid the hazy skies, there was a silver lining.
The 2013 haze crisis prompted regional governments to take action. Asean countries adopted a haze monitoring system and agreed to share satellite data to help better locate fire hot spots and determine if they are on land owned by plantation companies. Indonesia also ratified the Asean Agreement on Transboundary Haze Pollution.
5. Going after the culprits
The Transboundary Haze Pollution Act, passed in Parliament in August 2014, targets those responsible for causing or condoning fires if burning results in unhealthy levels of haze here.
Those guilty can be fined up to $100,000 a day, capped at $2 million, for causing unhealthy haze - defined as a 24-hour PSI value of 101 or greater for 24 hours or more.
The 2015 haze crisis saw the Singapore Government wielding its powers under the Act for the first time. The National Environment Agency (NEA) sent six Indonesia-based firms notices under the Act asking them to explain steps they are taking to put out and prevent fires on their land.
NEA also served Singapore-listed firm Asia Pulp and Paper (APP) a legal notice to supply information on its subsidiaries in Singapore and Indonesia, and the measures taken by its suppliers in Indonesia to put out fires in their concessions.
6. Be grateful for clean air: Jusuf Kalla
In March 2015, Indonesian Vice-President Jusuf Kalla rapped neighbouring countries for complaining about the haze, and asked them instead to be grateful for the clean air they enjoy for the rest of the year.
"For 11 months, they enjoyed nice air from Indonesia and they never thanked us... They have suffered because of the haze for one month and they get upset," he was quoted as saying in the Jakarta Globe.
It was a flashback to 2013, when Mr Agung Laksono, a minister in the previous government, hit out at murmurs from Singapore, which was then shrouded by the haze.
"Singapore shouldn't be like children, in such a tizzy," he said. Some days later, his colleague Jero Wacik warned Malaysia and Singapore not to "tell stories to the world".
7. Understanding PM2.5
Tiny pollutant particles 30 times smaller than the diameter of a strand of human hair are what makes haze dangerous, as they are small enough to enter the bloodstream and be carried to other organs. These particles are known as PM2.5.
NEA has been publishing one-hour PM2.5 concentration readings since 2014, but it announced in June 2016 that it will provide breakdowns of what constitutes normal to very high levels of one-hour PM2.5 concentrations.
This is to help the public make sense of the readings and plan their immediate activities.
For instance, the range of 0 to 55 micrograms per cubic metre (mcg/m3) is described as "normal", while anything above 250 mcg/m3 will be described as "very high".
8. Green awakening
If the 2013 haze moved governments to act, the crisis in 2015 did the same for consumers. There was a green awakening among consumers and businesses, which sought to be more responsible with their purchases and practices.
Consumers said they would boycott products from haze-linked firms, while firms distanced themselves from suppliers such as APP over supposed links to the haze. Supermarkets yanked APP products off their shelves after the Singapore Environment Council suspended the use of its Green Label on APP products.
Non-government groups, including volunteer group People's Movement To Stop Haze (PM.Haze) and WWF, launched campaigns such as We Breathe What We Buy to educate the public about how everyday choices - from buying cheese to toothpaste and lipsticks - could drive the palm oil industry where few employ sustainable or legal land clearing practices.
For more information, go to www.webreathewhatwebuy.com
On Oct 13, NTUC FairPrice chief executive Seah Kian Peng announced in a Straits Times forum letter that the supermarket now carries cooking oil from Roundtable on Sustainable Palm Oil (RSPO) certified sources.
Sources: WWF, ST Archive