Pushing for higher air quality

A NEW Pollutant Standards Index (PSI), to kick in from May, will expose the country's less-than-ideal air quality.

Under this new, higher standard, more days will be deemed "moderate" and fewer days deemed "good". This is because the new PSI will be expanded and is expected to be largely based on the prevalence of tiny and more hazardous pollutants called PM2.5 in the air.

PM2.5 refers to particulate matter up to 2.5 micrometers or microns in size. These particles are known to cause inflammatory responses both in the respiratory tract and blood vessels. Previously, the incidence of PM2.5 was not directly taken into account when determining the index.

Such particles generally come from activities that burn fossil fuels.

Nanyang Technological University's Professor Ang Peng Hwa was one of several experts who said that if "moderate" air quality becomes the norm here, pressure will be put on local polluters to improve their standards.

That norm would tell people that "at least some of this poor air quality is domestically generated, for example from urban traffic, and not all from fires in Indonesia. That could signal the Government to act on this," he said.

Comparing cities

HOW does Singapore's air quality compare with other cities?

Some experts such as National University of Singapore's (NUS) Assistant Professor Jason Cohen, who is studying how climate change and haze interact, said the level of air pollution in Singapore during non-haze periods is common in many cities. Even haze such as that seen this year is also not unusual.

Other researchers found that during 2007, Singapore's annual PM2.5 level was sandwiched between those of Los Angeles, Tokyo and London, which were better, and Hong Kong, Berlin and Mexico City.

Prof Cohen said, however, that Singapore's annual average may disguise peaks and troughs caused by seasonal monsoon, rain and fires, while other cities such as New York may have more consistent levels throughout the year.

In 2010, a United States-based air pollution research body, the Health Effects Institute, released a report showing that pollution in major Asian cities exceeded World Health Organisation (WHO) standards.

Like other cities, in recent years, Singapore's air quality standards have fallen below WHO guidelines for three other city-related pollutants - sulphur dioxide, ozone and PM10 (particulate matter up to 10 microns in diameter.


Local polluters

WHILE air quality is determined in part by one's geographical neighbourhood, experts say local polluters play a big role too.

The local emitters of sulphur dioxide, PM10 and PM2.5 include motor vehicles, refineries, power stations, shipping and other industries, said NEA.

Many of these same sources also emit nitric oxide, nitrogen dioxide and hydrocarbons which can also lead to ozone being formed.

Sulphur dioxide is a toxic gas, contributes to acid rain and helps to form PM2.5, while ozone and particulate matter pose respiratory risks.

To be fair, the Government has acted swiftly to raise air quality, especially targeting the worrisome sulphur dioxide, PM10 and PM2.5 pollution.

Diesel vehicles make up about half of all PM2.5 emissions in Singapore. Since January, all new diesel vehicles here have to meet tighter emissions standards. A higher standard for new petrol vehicles will kick in from April, while those for new motorcycles and new scooters will be tightened from October.

More incentives were also announced earlier this month to encourage diesel vehicle drivers to switch to more environmentally friendly models. Since last year, industries and motor vehicles here can use only diesel with less than 0.001 per cent sulphur.

The NEA said these and other measures also help to reduce the compounds that lead to ozone. These compounds form "an important fraction" of PM2.5, so their reduction will have additional benefits, said experts. Another major source of sulphur dioxide emissions is refineries. The NEA works with the Economic Development Board to reduce sulphur dioxide emissions from refineries.

The NEA's data showed that three refineries here made up 71 per cent of sulphur dioxide emissions in 2012. They are Shell, ExxonMobil and Singapore Refining Company (SRC).

Shell and ExxonMobil representatives said the firms had invested in new technology and improved operations over the years to reduce their emissions, and will continue to do so. SRC's upgrading plans include a facility to treat the petrol it produces to under 0.005 per cent sulphur.

An ExxonMobil spokesman said its investments had already helped avoid 215,000 tonnes of emissions each year in the past five years. He added that energy is crucial to society.

Minister for the Environment and Water Resources Vivian Balakrishnan said last week that Singapore's power plants have also increasingly switched to using cleaner natural gas.

All these efforts will help Singapore meet several interim WHO standards by 2020. It also aims to meet the WHO final standards at some unspecified point in future.

The way ahead

WHILE these steps are laudable, experts had suggestions for more improvement, particularly in the study of PM2.5. "A good next step (after the new PSI) would be to have the chemical and size breakdowns of the PM2.5 here," said NUS's Prof Cohen.

Knowing what makes up the tiny PM2.5 particles will make it easier for Singapore to determine when its neighbours are imposing the pollution and when local sources are the culprits, he said.

Singapore should also study the chemical processes that take place in the air. While vehicles emit PM2.5 directly, they also emit gases that interact with other airborne pollutants to create new PM2.5.

Research scientist Erik Velasco, from the Singapore-MIT Alliance for Research and Technology's Centre for Environmental Sensing and Modeling, said understanding Singapore's atmospheric chemistry will enable the Government to act to limit the prevalence of such particles.

Dr Velasco had also previously said that air quality management must also take into account seasonal shifts in weather patterns, such as the annual south-west monsoon.

Regional distribution of the pollutants also matters. The NEA now divides Singapore into five regions and gives updates on the six pollutants - PM10, PM2.5, carbon monoxide, ozone, sulphur dioxide and nitrogen dioxide. For instance, more than half of sulphur dioxide emissions here come from refineries located in the south-west, either on the mainland or offshore. When the wind blows from that direction during the monsoon, residents in those areas could be affected.

While Singapore's hands may be tied when it comes to foreign pollution, there is much it can do for itself.

Once the new PSI kicks in, Singapore will likely have many more days classified as "moderate", rather than "good". This could serve as a rallying point for the Government and the community to press for higher air quality standards. If that happens, everyone in Singapore will breathe a little easier.


Knowing what makes up the tiny PM2.5 particles will make it easier for Singapore to determine when its neighbours are imposing the pollution and when local sources are the culprits.

How the new index works

What is the new Pollutant Standards Index (PSI)? Why will it result in Singapore having more days of "moderate" air quality rather than "good"?

The new PSI index adds tiny, hazardous particles called PM2.5 to its current five "criteria pollutants". The five pollutants currently used are sulphur dioxide, ozone, carbon monoxide, nitrogen dioxide and PM10. The last refers to particles 10 micrometres or microns - about one-seventh the diameter of a strand of human hair - or smaller.

PM2.5 is a subset of PM10. It refers to particles 2.5 microns or smaller. They are considered dangerous because they can get into people's lungs to wreak harm.

The pollutant's levels here have exceeded World Health Organisation (WHO) air quality guidelines in six of the past seven years, partly due to the recurrent haze. Figures for last year are not available yet.

PM2.5 can be emitted by forest fires, vehicles, power plants, refineries, ships and aircraft, and to a lesser extent by construction and land reclamation. Many of these activities are found in Singapore and in cities in general.

Under the new PSI rules, the index will be based on whichever of the six pollutants is the most dangerously concentrated in the air. This is expected to be PM2.5.

The Government says the prevalence of PM2.5 in the air will probably set the new index "almost all of the time". This means many more days will be classified "moderate".

If the new PSI had been adopted, Singapore's air quality would have been "moderate", not "good", for over 90 per cent of the days for each of the past five years.

Based on the existing PSI, 91 per cent to 96 per cent of the days in each of the last five years had "good" air, and 4 per cent to 9 per cent had "moderate" air quality.

If the new PSI had been used, there would have been just 1 per cent to 4 per cent of "good" days in each year and 92 per cent to 98 per cent of the days would have had "moderate" quality air.

After "good" and "moderate", air quality worsens to "unhealthy", "very unhealthy" and "hazardous".

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