As PSI rises, sales of face masks soar
S'poreans also stock up on eye drops to protect themselves from haze
SINGAPOREANS are taking their own precautions as hazy conditions persist by stocking up on products to protect themselves.
Sales of products such as face masks and eye drops surged over the past few days, as the three-hour Pollutant Standards Index (PSI) reached a high of 155 on Monday night.
At Watsons, face mask and eye drop sales rose by 80 per cent and 50 per cent respectively, said its merchandising and marketing director Micheas Chan.
This amounted to more than 2,500 face masks and 1,000 boxes of eye drops being sold daily across its stores during this period.
Different measures of air quality
The Pollutant Standards Index, or PSI, has been Singapore's main indicator of air quality since 1991.
It measures air pollutants such as sulphur dioxide, nitrogen dioxide, ozone, carbon monoxide and PM10, which is particulate matter 10 microns or smaller in size - about one-seventh the diameter of a strand of human hair.
The PSI has a scale of 0 to 400. A reading above 100 is unhealthy, and anything higher than 300 is hazardous.
To keep the public updated on the recent haze situation, the National Environment Agency (NEA) has been publishing hourly updates of its three-hour average PSI reading on its website.
For example, a 3pm update is averaged from readings taken at 1pm, 2pm and 3pm.
The NEA also publishes the averages of the previous 24 hours at 8am, noon and 4pm daily.
Air quality indexes similar to the PSI are used in Australia, Hong Kong and Indonesia.
The PSI does not measure a smaller type of pollutant found in haze - the PM2.5, or very fine particulate matter.
These particles, about one-thirtieth the width of a human hair, are more hazardous because they can enter the lungs or bloodstream more easily than larger dust particles.
In addition to the PSI, NEA also publishes PM2.5 readings, averaged over 24 hours, of micrograms of PM2.5 per cubic metre.
Readings above 40 trigger health advisories.
The latest 24-hour reading at 4pm yesterday was 149-169.
- Other air quality indexes
There is no international consensus when it comes to air quality indexes. Unlike Singapore's PSI, official air quality indexes used by China and the United States measure PM2.5 levels in the air.
For example, Malaysia uses the Air Pollutant Index (API), which measures the same five pollutants as Singapore's PSI, but differs in the standards used to measure several of them.