PSI does not measure a smaller type of pollutant found in haze
Amresh Gunasingham Straits Times 11 Nov 10;
THERE could be a change in how the haze is measured in Singapore, and it may come as early as next year.
An ongoing review by the authorities could spell the end of the Pollutant Standards Index (PSI) for Singapore, which has been the main indicator of air quality for the past two decades.
The National Environment Agency (NEA) told The Straits Times that it is studying other indexes and the review will be completed by next year.
'We are looking at the types of pollutants they (other calculations) may take into consideration, that the PSI may miss out on,' said Mr Joseph Hui, director-general of the environmental protection division at the statutory board.
The PSI does not measure a smaller type of pollutant found in the haze, the PM2.5, exposure to which may cause heart attacks and other forms of cardiovascular deaths.
The PSI was adopted by the Republic 19 years ago; it was devised by the United States Environmental Protection Agency.
The PSI measures air quality on a scale of 0 to 400. Public health advisories are issued only when a reading exceeds 100, which puts it in the'unhealthy' range.
In 1999, the USswitched to the Air Quality Index (AQI), which also picks up smaller dust-like particles in the air, like PM2.5, as well as emissions from vehicles with diesel and petrol engines.Information on air quality is relayed to the public using a colour-coded scale based on readings that vary from 0 to 500.
There is no international consensus when it comes to air quality indexes. Malaysia, for instance, uses the Air Pollution Index (API) which also measures the PM2.5 levels in the air.
NEA has said the PSI had served Singapore well during haze episodes when it needed to issue public health advisories.
Climate scientists say a switch is timely, given the annual haze episodes, the latest of which struck last month when the air quality crept into the unhealthy range based on the PSI.
When choosing an index, countries have to weigh the risk factors peculiar to them. In Singapore's case, it is the haze, said Assistant Professor Koh Tieh Yong, who teaches at Nanyang Technological University's School of Physical and Mathematical Sciences.
Climatologist Matthias Roth from the National University of Singapore said what is missing with the PSI is the regular reporting of smaller particulate matter such as PM2.5.
'It has been known for a long time that it can be harmful. A better measure of the detrimental effects on health will be in line with the present focus of research,' he said.
NEA's Mr Hui said that if the agency adopts a new index, it will make sure it is easy for the public to understand. 'The public has been used to the PSI all these years, so with any new measurement, they must be able to correlate.'
Indexes measure different particles
Straits Times 11 Nov 10;
AIR quality indexes generally measure the amount of five known pollutants: sulphur dioxide, nitrogen dioxide, carbon monoxide, ozone and particulate matter.
But they differ in the types and sizes of particles they measure.
'The interpretation would be that if indexes measure different things, then the corresponding health effects will also differ,' said climate scientist Koh Tieh Yong of Nanyang Technological University.
Health experts have linked exposure to PM2.5, a pollutant that is 30 times thinner than the width of a human hair, to heart attacks and other forms of cardiovascular deaths. It can penetrate deeper into the lungs and carry more concentrated toxic substances, such as metals and endotoxins, compared to PM10, which is larger.
The National Environment Agency monitors PM2.5 levels through 11 weather stations across the island, although this information is not made available to the public on its website daily.
Instead, the agency gives a yearly average reading, which is found in its annual report.
