NEO CHAI CHIN Today Online 9 Oct 15;
SINGAPORE — Poor visibility during haze episodes is not always caused by air pollutants, the authorities said today (Oct 8).
Questions about the accuracy of Pollutant Standards Index (PSI) readings and Singapore’s reporting of air quality have persisted and the National Environment Agency (NEA) held a media briefing today to tackle some of these.
There is poor visibility when PSI levels are high, but “poor visibility can sometimes be things other than PSI”, said Dr Felicia Shaw, director of risk and resource at the Meteorological Service Singapore (Met Service).
In the face of calls for one-hour PSI readings, Ms Indrani Rajaram, project director and chief scientific officer of NEA’s pollution control department, reiterated that the public should instead be using the raw one-hour PM2.5 data for various areas of the island as a gauge to take the “necessary action”.
“If tomorrow there’s a health study, a very rigorous health study, that comes out and tells us one-hour PM2.5 concentration is harmful, we’ll use that to do a conversion (to get one-hour PSI). But at the moment the studies out there don’t give you a number that is supported by health studies to do this computing,” she said.
PM2.5 is fine particulate matter that is the pollutant of concern during the haze. Moisture is among the factors affecting visibility, as water droplets scatter light and some smoke particles attract water molecules around them, Dr Shaw explained.
Sulphates — one such water-attracting pollutant — could also lead to deterioration in visibility, and a theory is that particulate matter from the forest fires in Indonesia is rich in sulphates because the biomass has been exposed to volcanic sulphur dioxide.
The Met Service charted the relationship between visibility, PM2.5 and relative humidity for the past month and found that visibility remained poor when PM2.5 levels are lower, so long as conditions were humid. Charts of 2013 and 2014 haze months also show that the thickest haze produces the worst visibility but this was coupled with dry conditions when relative humidity was below 80 per cent.
To calculate the 24-hour PSI, concentrations of each PSI component — sulphur dioxide, oxides of nitrogen, carbon monoxide, ozone and particulate matter (PM10 and PM2.5) — are averaged over 24 hours and converted to a sub-index (a number) via a series of computations. The highest sub-index is the 24-hour PSI.
The NEA began publishing three-hour PSI readings in 1997 to provide an indication of “current levels of air quality”, said Ms Indrani. Unlike 24-hour PSI readings, however, three-hour PSI readings are not tied to health advisories issued by the Health Ministry.
Ms Indrani also said the NEA will enhance the presentation of data on its myENV app. This is in response to feedback from the public, who have said that the numbers appearing on the app are not very clear due to the colours used, and that they would like to see PM2.5 fluctuations pictorially, instead of the numbers being presented in a table and for only a six-hour period.
“So these are some of the things we’re now looking into, to see how best to present the data. This is work still in progress,” she said, without divulging when the improvements would be rolled out.
The NEA has 22 air monitoring stations islandwide, each costing over S$300,000. Each component of the PSI is measured by analysers that are regularly calibrated. Real-time data from the stations are transmitted to a system that converts the feeds to average values and computes the PSI automatically.
The 24-hour PSI stood at a moderate 70 to 80 at 8pm today, and the one-hour PM2.5 was 35 to 52 microgrammes per cubic metre. Air quality is expected to be in the moderate range tomorrow, said the NEA.
Meanwhile, pharmacy chain Watsons Singapore has confirmed it does not stock the Paseo, NICE and Jolly brands of paper products that are related to Asia Pulp & Paper Group (APP). The pharmacy chain is among those sent forms from the Singapore Environment Council and the Consumers Association of Singapore, asking them to declare that they have not procured or used wood, paper and/or pulp materials from the companies accused of causing fires in Indonesia.
Last month, NEA sent preventive measures notices to five Indonesian firms to deploy fire-fighting measures under the Transboundary Haze Pollution Act. APP was asked to provide further information, which it acceded to last week.
In a statement today, Watsons Singapore’s chief operating officer Dominic Wong said: “We are working with all our suppliers to run an audit to ensure that their products supplied to us are not directly procured from the six companies accused of contributing to the haze pollution.”
Why it could look hazy even though PSI levels are low
What affects visibility other than air quality? Is rain during the hazy period acidic? Which PSI reading should one refer to? The National Environment Agency answers these questions in an "educational session" at its headquarters.
Justin Ong Channel NewsAsia 8 Oct 15;
SINGAPORE: What you see is not what you get when it comes to the haze, said the National Environment Agency (NEA) on Thursday (Oct 8). This is because visibility can be influenced by factors other than air pollutants, such as humidity and weather.
NEA said it conducted an analysis from Sep 9 to Oct 6, a rainy period when Pollutant Standard Index (PSI) levels appeared "lower" than the thick haze that hung over Singapore. It looked at the correlation between PM2.5 concentration and visibility and its analysis revealed visibility remained poor when the concentration of PM2.5 particles was lowered, so long as conditions were humid.
A PM2.5 concentration of 60µg/m3 under high humidity or rainy conditions also gave the same visibility as a PM2.5 concentration of 250µg/m3 under drier conditions, the agency added. But poor visibility can persist even when the air starts to dry out, and even after humidity readings drop.
Dr Felicia Shaw, director of NEA's risk and resource department, explained why: "Rain can wash out many but not all of the sulphate particles and the situation is complicated when more haze blows in from Indonesia while it's raining."
She also addressed concerns of rain during the hazy season being perceived as acidic in nature: "Sulphur dioxide is released during burning in Indonesia, but it has to travel hundreds of kilometres to Singapore and will become sulphate particles then."
There was also "no change in rainwater PH levels during the haze", confirmed Ms Indrani Rajaram, NEA's chief scientific officer, who added that the acrid smell given off by the haze is due to a combination of gases rather than a particular one.
"Vegetation burning (in Indonesia) gives out a complex mix of gases. You cannot pinpoint which one produces which smell. It also depends on where and what is burning," she said.
HOW AIR QUALITY IS MEASURED
During the "educational session" held at the Environment Building, NEA also explained how air quality is measured. While air quality internationally is usually measured by the concentration of six different air pollutants - sulphur dioxide, oxides of nitrogen, carbon monoxide, ozone and particulate matter (PM10 and PM2.5), PM2.5 is the pollutant of concern during hazy periods, said NEA.
In Singapore, there is a network of 22 air monitoring stations with automatic analysers to continuously monitor the six key air pollutants, with one dedicated analyser for each pollutant, the agency added. The analysers are certified by the US Environmental Protection Agency as an equivalent method of measuring air quality.
Real-time data from the station is transmitted to NEA's Data Management Systems (DMS) at regular intervals. The DMS then converts the data to average hourly and daily values, which then computes the Pollutants Standards Index automatically.
NEA also noted that there are smaller, low-cost handheld devices available for particulate matter (PM) monitoring. While they are able to indicate PM levels, these devices are not accurate or certified for PM measurements. For instance, moisture in the air could lead to inflated readings on a handheld device.
The 24-hour PSI is the number to look out for in terms of taking precautions, said NEA, because health studies on effects of exposure to particulate matter have been based on this duration. 3-hour PSI and 1-hour PM2.5 levels are better used for immediate activities such as jogging.
"While raw numbers themselves are a good indication of how bad the haze is, it all also depends on how much time you've been exposed, the type of activity, health status, age etc.," said Ms Rajaram.
- CNA/dl/hs
NEA: No to 1-hour PSI
Mrs Indrani Rajaram with a machine used by NEA to help measure the concentration of PM2.5 in the air. Converting raw pollutant concentration data into one-hour PSI readings is not supported by health studies, she said.
Audrey Tan, Straits Times AsiaOne 9 Oct 15;
The National Environment Agency (NEA) will not heed calls for it to provide one-hour Pollutant Standards Index (PSI) readings.
This is because converting raw pollutant concentration data into one-hour PSI readings is not supported by health studies, said project director and chief scientific officer Indrani Rajaram from the NEA's pollution control department yesterday.
The NEA calculates PSI by inputting pollutant concentration data into a formula that takes into account breakpoints - upper and lower concentration limits derived from health studies.
"If tomorrow, there is a very rigorous health study that tells us that (there is a) one-hour PM2.5 concentration that is harmful, we will use that to do a conversion.
"But at the moment, studies out there don't give you a number supported by health studies."
She urged people to use three-hour PSI readings or one-hour concentrations of PM2.5 - the dominant pollutant during periods of haze - as "an indicative measure to make adjustments to daily activities". As a gauge, the maximum concentration of PM2.5 on a regular, non-hazy day is usually between 20 micrograms and 35 micrograms per cubic m. It becomes a serious problem when the numbers hit 100, and dangerous when it exceeds 200.
The haze on Sunday, when it was not as bad as other days. When PSI readings fluctuate and air quality does not always correspond with the smell and look of the air, hourly readings can help people plan their days better.
Mrs Indrani stressed that the three-hour PSI is not a gauge of whether the air quality is good, moderate or hazardous - bands based on only the 24-hour PSI. Many have called for hourly PSI readings to better plan their activities.
The NEA also said it is looking at ways to improve the user interface on its MyENV app and website.
Official one-hour PSI figures, please
Audrey Tan Straits Times 8 Oct 15;
The haze is back with a vengeance, and this year's seasonal episode is well on its way to becoming the worst on record.
Foul-smelling air and health concerns aside, the haze has also cast a pall on the National Environment Agency's (NEA) ability to provide timely air quality readings.
The Pollutant Standards Index (PSI) readings posted on www.haze.gov.sg do not provide up-to-date information which people can use to plan their day, say some individuals, volunteer groups and organisations, which are turning to at least three different alternative sources to judge how hazy it is here at any given moment.
Their issue is this: Amid periods of intense haze, when PSI readings fluctuate and air quality does not always correspond to the smell and look of the air, hourly PSI readings are needed to help people better plan their activities to avoid exposure to air pollution at its worst.
The NEA website provides 24-hour and three-hour PSI readings that measure the average concentration levels of six component pollutants over the given period. These readings are accurate and reliable. But they do not provide information on actual conditions, says Dr Erik Velasco, an air pollution researcher from the Singapore-MIT Alliance for Research and Technology.
On top of the consolidated PSI readings, the haze website also provides breakdowns of the concentrations of individual pollutants. It gives hourly concentrations of nitrogen dioxide and PM2.5 - the main pollutant in transboundary haze. It also provides eight-hour concentrations of carbon monoxide and ozone, and 24-hour concentrations of PM2.5, PM10 and sulphur dioxide.
These readings are complicated - they have different hourly averages and different measurement units, such as milligrams per cubic metre for carbon monoxide and micrograms (mcg) per cubic metre for the others.
Said Mr Kavickumar Muruganathanm, head of eco-certifications and lead environmental engineer from non-government organisation the Singapore Environment Council (SEC): "To the man in the street, he would find it hard to evaluate and interpret these figures.
"A uniform index-based reporting system would be useful for easy understanding of the air quality based on individual pollutants for a layman."
A one-hour PSI reading could do just that.
Now, NEA says that although there have been recent studies on sub-daily or shorter PM2.5 exposure, "the evidence of these studies is not sufficient for the development of one-hour PSI".
This has not stopped volunteer groups, such as the People's Movement to Stop Haze (PM.Haze), from taking matters into their own hands. The group calculates one-hour PSI readings for north, south, east, west and central Singapore by using the one-hour PM2.5 concentration data and mathematical formula found on NEA's website.
Group president Tan Yi Han said: "The rationale is simply to provide more accurate information of the current pollution level that a person is being exposed to.
"As one-hour PM2.5 concentrations are already being provided for each region, why not display it in the PSI format?"
But, to put things in perspective, on a day when PM2.5 levels hit 100mcg per cubic metre, a person will take in around 1,100mcg of these pollutants if he stays outdoors throughout the day. This is much less than the amount of PM2.5 pollutants a smoker will inhale for every cigarette consumed, which is in the range of 10,000mcg and 40,000mcg.
On a regular, non-hazy day, the maximum concentration of PM2.5 is usually between 20 and 35 mcg per cubic metre, said an expert. They start becoming a serious problem when the numbers hit 100, and dangerous when they exceed 200.
The authorities here also base health advisories on the 24-hour PSI as scientific, and epidemiological studies on the health effects of particulate matter have been based on these measurements.
Experts acknowledge that more studies are needed to investigate the impact of short-term exposure to haze on health. But many point out that one-hour PSI readings should still be provided to help people decide on personal protection measures.
Mr Tan noted that 24-hour PSI readings take 24 hours to reflect changes in air quality, even if PM2.5 levels swing drastically.
Last Saturday, for instance, the one-hour PM2.5 reading at 4pm was 200mcg per cubic metre. At 5pm, it rose to 252mcg per cubic metre. "People who rely on the 24-hour PSI may have been doing strenuous outdoor activities for the whole day and exposing themselves to a very unhealthy dose of pollution," he said.
So, instead of the official website, people are turning to websites such as by.originally.us/psi/real or aqicn.org for haze updates. This is less than ideal, as it means misinformation can spread easily.
Just a few weeks ago, a rumour claiming the Government had seeded clouds to clear the skies for the Formula One race was circulated. It implied that the resultant rain was harmful.
The information was untrue.
As Dr Velasco put it: "The main goal of the PSI should be to communicate... air quality conditions using a simplified scale with no technicalities. Having an index for each pollutant won't be practical or efficient to communicate with the public."
The NEA took a step in the right direction when it included concentrations of PM2.5, the main pollutant of concern, into PSI calculation last year. Providing one-hour PSI readings should be its next goal.
