The next time you click on the NEA website
for your dose of the hourly PSI, you'd want to keep an eye on the "PM2.5" indicator as well.
Small, yet potentially deadly – PM2.5 is one of the reasons why the haze-filled air around you appears murkier and more acrid-smelling than the Pollution Standards Index (PSI) number suggests. The PSI is an indicator of the level of major air pollutants, including PM10 – a class of particles which includes the PM2.5. Unlike the United States, which uses the Air Quality Index (AQI) – an aggregation of the levels of PM2.5, ozone and other major air pollutants – Singapore's National Environment Agency (NEA) has both the PSI and PM2.5 indicators on its site.
PM2.5 – the acronym for fine particulate matter (PM) 2.5 micrometres in diameter or smaller – refers to the minute particles which pollute the air. These include combustion particles – from motor vehicles and the forest fires in Indonesia – and other substances. PM10 refers to particulate matter, such as such as dirt, dust and mould, which are 10 micrometres in diameter or smaller. Larger particles in the air with sizes ranging from larger than 2.5 to 10 micrometres in diameter are sometimes called coarse inhalable coarse particles. In comparison, the size of a single strand of human hair is between 50 and 70 micrometres in diameter.
Triggers Respiratory Illnesses
Studies conducted by Beijing University in China have directly linked PM2.5 to aggravated asthma conditions, lung problems and heart attacks. PM2.5 is so deadly because it is small enough to be inhaled into the bloodstream and the deepest regions of our lungs. Coarser PM10 particles, on the other hand, are normally more benign because they are usually trapped by the nasal passages or pass directly through the body.
Watch For The Big 40
So snap on the N95 mask when the PM2.5 reading exceeds 40, says an expert from the Singapore Environment Council. It’s an indication of unhealthy PM2.5 levels in the air. The 24-hour PM2.5 Concentration (µg/m3) in Singapore crept pass the 200 mark on Jun 20, 2013. The World Health Organisation (WHO) appears to be more conservative – recommending no more than 25 micrograms of PM2.5 in the air over a 24-hour average (25 μg/m3 24-hour mean).
Photograph courtesy of The Straits Times