SINGAPORE - People should not switch on their fans at home when there is haze, because it will stir up indoor particles.
And children are safe staying in classrooms rather than outdoors if the windows and doors are kept closed - even if they lack air- conditioning.
This advice came from three experts who took part in a special one-hour online forum on the haze yesterday, organised by The Straits Times to answer public queries about the pollution.
The forum was dominated by health-related questions amid fears about possible long-lasting effects.
The experts noted that the best way to protect against the haze was to follow the Government's health advisories and wear face masks outdoors when the air quality becomes unhealthy.
Said Dr Erik Velasco, a research scientist at the Singapore-MIT Alliance for Research and Technology: "You have to make sure the mask fits perfectly on the face."
He added that even stubble could cause gaps in the mask that allow particles to be inhaled.
Dr Ong Kian Chung, a respiratory medicine specialist at the Mount Elizabeth Medical Centre, noted that there is no scientifically proven way to purge small, toxic particles called PM2.5 from the human body.
Besides wearing face masks outdoors, people could use indoor air purifiers to protect themselves. The National Environment Agency has a recommended list of purifiers on its website, he said.
The forum's third expert was Dr Santo Salinas, a senior research scientist at the Centre for Remote Imaging, Sensing and Processing at the National University of Singapore.
He studies atmospheric radiation and aerosols, and remote sensing.
Even though the skies here have cleared and the air quality is "good" again, the Government and scientists have warned that the haze could return in the next few months.
This is because Indonesia's dry season lasts until September, and the raging fires there which led to the haze in Singapore may not have been fully extinguished.
Last month's haze was the worst in Singapore's history, with the three-hour Pollutant Standards Index (PSI) hitting a record 401 at noon on June 21.
Air becomes hazardous when the index crosses 300.
Before this year, the previous PSI record was 226 in 1997.
Why was the haze so bad this year?
Dr Santo Salinas: In the Philippines and Taiwan, there were storms that pulled the moisture north and created a dry spell in our region. That was a unique event that led to the burning becoming worse. It's not likely to be repeated in the next three or four months, but we are at the beginning of the dry season, so we are still likely to get smoke from the burning.
Where did the haze go? Will it be back?
Dr Salinas: As long as the fires in Indonesia are still burning, the haze won't be gone. It's just that the winds changed directions. A lot of burning in Indonesia is on peat soil, so the fires could have been underground and difficult to detect from our satellites.
Dr Erik Velasco: We have to be prepared for more smoke haze events until the end of the dry season. These wildfires are not very aggressive or intense, can linger for many days and don't produce many tall plumes.
Why use PSI and not the Air Quality Index?
Dr Velasco: The PSI includes five criteria pollutants - ozone, PM10, nitrous oxides, sulphur dioxide and carbon monoxide. The standard index doesn't include fine aerosols. These were picked by the US in the late 1970s and 1980s; at that time, we didn't know much about fine aerosols and didn't have the instrumentation to monitor them.
Today, we do. That's the reason many environmental agencies around the world report both pollution indices and PM2.5.
In Singapore, the PSI doesn't include PM2.5 as a stand-alone pollutant. It's true that PM10 includes PM2.5. However, the fraction of PM2.5 in PM10 is not always the same. For example, we may have 100 micrograms/m3 of PM10 during a haze event - 80 to 90 per cent of that might be PM2.5. But in another event with 100 micrograms/m3 of PM10, less than 20 per cent might be PM2.5, and that makes a huge difference. On a normal day in Singapore, the fraction of PM10 that is PM2.5 might be 55 to 70 per cent.
Can the body cleanse itself of PM2.5?
Dr Ong Kian Chung: Once these foreign bodies are in there, they will cause inflammation which would have taken place once these particles are in the body. Once in the bloodstream, they go anywhere in the body and it will be very difficult for the body to cleanse it.
How much PM2.5 have we been exposed to over the past weeks and how does it affect health?
Dr Ong: The fraction of PM2.5 to PM10 is over 80 per cent, which is more than the usual that we have been breathing in. What can we do about it? Nothing much now. To prevent further inhalation when levels are high, avoid going outdoors and wear the appropriate masks.
Can I jog with a mask on?
Dr Ong: I don't think it's a good idea; it's counterproductive. The reason you jog is to improve your health. When the haze is bad, pollution is high and you're exposing your body to more pollutants.
Should we be concerned about indoor air quality?
Dr Velasco: We compared pollution indoors and outdoors, and there was a big surprise: Air-conditioners, if they're in good condition, can remove an important fraction of outdoor fine aerosols.
We found that air-con systems in train stations and in the MRT are very good - these are very preliminary results and have to be studied in more detail.
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