Friday, 9 October 2015

NEA: No to 1-hour PSI

By Audrey Tan, The Straits Times, 9 Oct 2015

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.

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.

NEA explains why it does not give hourly PSI readings
By Neo Chai Chin, TODAY, 8 Oct 2015

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.”

Haze: Experts divided on effect of high PM2.5 levels
Some say even a single exposure could be potentially harmful, while others disagree
By Carolyn Khew, The Straits Times, 21 Oct 2015

The one-hour PM2.5 pollutant reading reached a record high on Monday (19 Oct) but experts are divided on how harmful that will be to health.

While some say even a one-time event could be considered potentially hazardous according to standards set by the United States Environmental Protection Agency (EPA), there are others who believe that only prolonged exposure to high PM2.5 concentration levels should be a cause for concern.

On Monday, the National Environment Agency (NEA) said the PM2.5 concentration level of 471 in the western areas of the country at 11pm was the highest recorded so far this year. Conditions on that day had deteriorated sharply in several parts of the island after denser haze from areas south of Singapore was blown in by the prevailing winds.

Senior research scientist Santo Salinas at the Centre for Remote Imaging, Sensing and Processing at the National University of Singapore said that according to the EPA, PM2.5 concentrations higher than 65.5 micrograms per cubic metre are considered "unhealthy limits and potentially hazardous."

"I would say anything above 65 micrograms per cubic m is potentially harmful and steps should be taken to protect the more vulnerable," said Dr Salinas.

PM2.5 pollutants are smaller than 2.5 microns in diameter, or a 30th the diameter of a human hair, and unlike coarser particles, the body is not equipped to filter them out. Long- term exposure to them on a regular basis has been linked to increased risk of death from complications such as lung cancer or heart disease.

The short exposure to PM2.5 concentrations over one or two hours at a level like Monday's exacerbates respiratory and cardiovascular illnesses in addition to irritation of the throat and nose, said research scientist Erik Velasco from the Singapore-MIT Alliance for Research and Technology. "My recommendation is to check constantly the one- hour PM2.5 concentrations reported every hour by NEA," said Dr Velasco. "If the current concentration is over 150 micrograms per cubic m, try to stay indoors."

The NEA has stated that only the 24-hour Pollutant Standards Index (PSI), which takes into account the PM2.5 concentration levels, is used as a basis for the health advisories issued by the Ministry of Health.

Associate Professor Richard Webster, from the Nanyang Technological University's School of Physical and Mathematical Sciences, said the spike is only really significant if it lasts for several days.

Compared with cigarette smoking, said Prof Webster, the total amount of PM2.5 breathed in over 24 hours' exposure to a concentration of 471 micrograms per cubic m would still be less than half the PM2.5 found in one cigarette. He said the true health effects of PM2.5 from environmental samples are not yet accurately known.

"Cigarette smokers experience astronomically higher PM2.5 levels than what is given on the PSI scale and many live to old age, or at least the effects of smoking cigarettes do not catch up with them for many years. This would imply that the classifications on the health effects of the PM2.5 (unhealthy, hazardous, etc) are considerably overestimating the seriousness of the problem, at least in the short term," he said.

"The best thing to do is to carry on as normal and not to worry about it too much. However, people who exercise vigorously might like to slow down when the PSI level gets very high, since the amounts that they breathe in will increase proportionally to their breathing rate."

In its advisory yesterday, NEA said the 24-hour PSI for the next 24 hours is expected to be in the low to mid sections of the unhealthy range, and may improve to the high end of the moderate range if winds are favourable.

As of 7pm yesterday, the 24-hour PSI reading was at 93-167.

Tough to pinpoint haze culprits
NEA does not engage in cloud seeding to clear haze: Vivian Balakrishnan
Government lays out measures to tackle effects of haze

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