New index reflects air toxicity better as tiny particles are most harmful
By Feng Zengkun, The Straits Times, 12 Mar 2014
By Feng Zengkun, The Straits Times, 12 Mar 2014
The move is timely as it gives a better picture of the toxicity of the air as the PM2.5 can enter people's lungs and blood to cause harm, said experts interviewed.
Minister for the Environment and Water Resources Vivian Balakrishnan said as much when he announced the change in Parliament yesterday.
"This revised single index will reflect whichever of six pollutant parameters is the worst.
Many people had called for more data on PM2.5 last year, during Singapore's worst haze episode, owing to its health impact.
Nanyang Technological University's Professor Ang Peng Hwa, who created the Haze Elimination Action Team Facebook campaign in 2007, said the new PSI "reports more accurately the situation, that PM2.5 is bad for health".The National Environment Agency (NEA) said yesterday that based on the present PSI, each of the past five years had between 91 and 96 per cent of "good" air quality days, and just 4 to 9 per cent of "moderate" days.
But with the revised PSI, the figures would be 1 to 4 per cent of "good" days each year and 92 to 98 per cent of "moderate" days.
NEA said: "There will be no change to normal routines on the ground as people can carry on normal activity if air quality is in the 'good' or 'moderate' range."
The current PSI is calculated from the worst of five other pollutants: sulphur dioxide, ozone, nitrogen dioxide, carbon monoxide and particles called PM10.Another change taking place in May is that the Government will give hourly updates that are more current on PM2.5 levels in the air.
Now, the updates are given hourly too but are averaged from readings in the previous 24 hours.
With the new hourly and more current PM2.5 updates, NEA will publish a lot more raw data that is useful for academics and scientists, Dr Balakrishnan said.
Last night, the three-hour PSI also crept up to 84 at 8pm, close to the unhealthy range. NEA said it was because of hot spots in southern Johor. The number of hot spots detected in Peninsular Malaysia rose to 149 yesterday from 86 on Monday, while those in Sumatra numbered 259, up from 228, the agency said.
PM2.5 pollutants hit unhealthy level
Yesterday's reading triggers warnings for some to limit outdoor exercise
By Grace Chua, The Straits Times, 13 Mar 2014
Yesterday's reading triggers warnings for some to limit outdoor exercise
By Grace Chua, The Straits Times, 13 Mar 2014
This is even as the main Pollutant Standards Index (PSI) stayed in the moderate range. At 9pm last night, the 24-hour PSI in various parts of the island ranged from 48 to 70.
But PM2.5 levels hit 60 micrograms per cubic m at several points in the afternoon, the highest reading this year. A reading above 55 mcg would be considered unhealthy under a new way of calculating the PSI from May.
At these levels, the elderly, children and those with heart or lung disease should reduce prolonged or heavy outdoor exertion, while everyone else should limit it, said an advisory on the National Environment Agency (NEA) website.
This development comes a day after the Government announced it would incorporate PM2.5 levels into the calculation of the overall PSI starting in May.
PM2.5 are fine particles in the air smaller than 2.5 microns in diameter. Currently, the PSI value is based on the worst of five pollutants, including larger PM10 particles up to 10 microns in diameter.
From May, after PM2.5 becomes a PSI component, yesterday's levels of PM2.5 would translate to a PSI value of 105, in the "unhealthy" range, the NEA said.
Meanwhile, the short-term PSI tends to rise in the evenings and some think the smell gets worse. Without the sun's heat, experts explained, air in the boundary layer of the sky contracts and pollutants within it become more concentrated. The atmospheric boundary layer is the stratum of air closest to the earth's surface, and it expands and contracts as it gains or loses heat.
But while the haze might smell bad, its odour cannot be used to judge how harmful it might be, said Dr Erik Velasco, a research scientist who studies air pollution at the Singapore-MIT Alliance for Research and Technology. "The acrid smell is due to the chemical composition of the pollutants, which depends on the soil, biomass and fire characteristics."
He added: "The intensity of smell cannot be used to quantify the concentration of pollutants in the air. Both visibility and smell are just qualitative indicators."
On Tuesday, the NEA had said the current hazy conditions were due to southern Johor hot spots. The NUS Centre for Remote Imaging, Sensing and Processing also captured images of smoke plumes at plantations near Kota Tinggi in Johor, and its senior research scientist Santo Salinas said: "Because it's extremely dry nowadays, this is something that could have happened accidentally."
There are also hot spots in other parts of peninsular Malaysia and northern Asean, and smoke haze over central Sumatra.
There are also hot spots in other parts of peninsular Malaysia and northern Asean, and smoke haze over central Sumatra.
Short-term exposure to PM2.5 is harmful too
High levels of tiny particles damaging to elderly and children, say experts
By Feng Zengkun and David Ee, The Straits Times, 13 Mar 2014
High levels of tiny particles damaging to elderly and children, say experts
By Feng Zengkun and David Ee, The Straits Times, 13 Mar 2014
WHILE studies have established that prolonged exposure to the pollutant PM2.5 can be highly hazardous, some experts have warned that even short-term exposure can be damaging.
For the elderly, being exposed to high levels of the tiny particles for just an hour can lead to higher risks of heart attacks, a recent study suggested.
One in five children here has asthma and the symptoms may worsen if exposed to high PM2.5 levels for even a few minutes, said research scientist Erik Velasco of the Singapore-MIT Alliance for Research and Technology's Centre for Environmental Sensing and Modelling.
One in five children here has asthma and the symptoms may worsen if exposed to high PM2.5 levels for even a few minutes, said research scientist Erik Velasco of the Singapore-MIT Alliance for Research and Technology's Centre for Environmental Sensing and Modelling.
Experts said this is why the Government's decision to revise its air quality reporting system is timely. From May 1, the National Environment Agency (NEA) will add PM2.5 to its five other pollutants for calculating the Pollutant Standards Index (PSI). This means that if PM2.5 is the most significant pollutant in the air, the PSI figure will be based on it.
The NEA will also begin giving new, hourly PM2.5 updates based on the previous hour's readings. It gives hourly updates now but these figures are based on data in the previous 24 hours and may not reflect the air quality as well at any given time.
PM2.5 particles, which can enter people's lungs, make up the majority of haze particles - as much as 80 per cent during last year's record-busting pollution. They must be watched closely.
The existing PSI is usually based on PM10, which are particles 10 microns or smaller. The Government had said PM10 includes the smaller subset of PM2.5, so an increase in the tiny particles will be reflected in the PSI.
However, experts said PM10 is measured by the weight of the particles per cubic metre of air. This means two pockets of air could both have 100 micrograms of particles - and thus create the same PM10 and PSI values.
But one pocket of air could have fewer but larger particles, while the other could have more of the smaller, more toxic PM2.5 particles.
The NEA reckoned, based on existing PSI calculations, that each of the past five years had between 91 per cent and 96 per cent of "good" air quality days, and just 4 per cent to 9 per cent of "moderate" days.
Under the new reporting system, the figures would have been flipped, with just 1 per cent to 4 per cent of good days in each year, and 92 per cent to 98 per cent of moderate days.
"NEA will have to acknowledge that it was a bit conservative on quantifying the risk posed by the smoke," said senior research scientist Santo Salinas at the National University of Singapore's (NUS) Centre for Remote Imaging, Sensing and Processing.
The NEA's PSI health advisories for moderate and good air are the same. They state that all people, even the vulnerable, can carry on normal activities unless they feel unwell. However, scientists said the vulnerable should take extra care when air quality is moderate.
Dr Salinas welcomed the new, more current hourly PM2.5 updates, which will be provided alongside the 24-hour averages. "A 24-hour average smooths out pollution spikes," he said. "It is not a good indicator for rapid reaction, for example, for people who work outdoors."
Dr Christopher Frey, chair of the United States Environmental Protection Agency's clean air scientific advisory committee, explained that the first generation of PM2.5 monitors needed to accumulate almost a full day's worth of particles to be useful.
Instruments that can measure PM2.5 over shorter time frames are a "relatively recent introduction" so there have not been enough health studies to reach a firm conclusion on the short-term exposure impact, he said.
Dr Velasco stressed: "There is no evidence of a safe level of exposure or threshold, below which no adverse health effects occur."
Some complained during last year's haze that NEA figures - averaged over periods longer than an hour - did not seem to match what was outside their windows.
Dr Frey said the new one-hour index will "change more quickly and be more consistent with people's observations of visibility reduction".
Nanyang Technological University Professor Ang Peng Hwa, who created the Haze Elimination Action Team Facebook campaign in 2007, said the new changes "were made in response to science". He added that the new system may highlight pollution generated here, which could signal the Government to take action.
Assistant Professor Harvey Neo of the NUS Department of Geography said: "Some people will get a sense that this was a long time coming, or feel they have been cheated for the past few years.
"But most would welcome the changes... I would see this as (the Government) trying to match reality better."