Is indoor air safer? 7 things to know and ways to stay protected in this prolonged haze season

SINGAPORE: Staying indoors with the windows shut may seem the safest way to escape the haze. But just how much cleaner is the air in your home?

When CNA’s Talking Point tested the air quality in a fifth-floor flat whose windows had been closed for an hour, the PM2.5 reading of 187 micrograms per cubic metre was higher than the level outdoors, which was 169.

The finding comes as Singapore grapples with its worst haze episode since 2015, with 20 consecutive days of unhealthy air recorded as at Oct 24, surpassing the 15-day streak in 2015.

As the haze persists, there is public concern about prolonged exposure to PM2.5, the predominant pollutant during periods of transboundary haze.

PM2.5 particles, which are roughly 30 times smaller than the width of a human hair, can penetrate deep into the lungs and cause inflammation.

Prolonged exposure has been linked to increased risk of a stroke and lung cancer, among other things, highlighted respiratory physician Steve Yang from The Respiratory Practice.

So, viewers have written to Talking Point to ask how best to protect themselves. Does air-conditioning help? Do expired N95 masks still offer protection? And which air quality standards should they rely on?

Programme host Diana Ser met the experts to look at seven things that Singaporeans should know during this haze season.

WATCH: How harmful is the haze and how can we protect ourselves? (23:20)

1. WHAT IS YOUR INDOOR AIR QUALITY LIKE?

In the first flat Ser visited, where the air quality was worse than outdoors, the windows were open in the morning before the resident closed them.

“It’s entirely possible that the windows were closed … (when) the PM2.5 levels were higher, thereby trapping the polluted air,” said Nanyang Technological University (NTU) assistant professor Leonard Ng, who used a professional-grade air quality monitor to record the measurements.

In a 15th-floor flat in the same block, where the windows were also closed for an hour, the reading was lower at 149 but still elevated. When they opened the windows, it climbed to 301 as the haze worsened.

As there is stronger airflow on a high floor, haze particles get blown indoors faster even as these homes are less exposed to traffic emissions, said Ng. “If the air quality is poor outside, it’ll be poor inside as well.”

He advised opening the windows at home only when the outdoor air quality “isn’t that bad”.

2. HOW MUCH CAN AIR-CON OR AIR PURIFIERS HELP?

When the air-con in one bedroom in the 15th-floor flat was run for 10 minutes, the PM2.5 reading dropped from 131.6 to 109.8, which was still in the elevated band.

While most air-con units have built-in filters that remove some airborne particles, they are not designed to “fully clean your air”, said Ng.

When an air purifier was run for an hour in the living room, however, the PM2.5 reading dropped to 40.7, within the normal band.

While the tests were conducted under different conditions and with different durations, the findings suggest that the air-con is no substitute for an air purifier.

For those considering an air purifier, Ng advised choosing one based on room size — by checking its clean air delivery rate, which measures the volume of clean air produced and thus the purifier’s effectiveness in that space.

While high-efficiency particulate air filters will capture fine airborne particles, they are not essential, he added. A regular filter rated for removal of PM2.5 particles can also be used.

He also recommended running the air purifier for an extended period with the doors and windows closed, while keeping its vents unobstructed.

3. CAN EXPIRED N95 MASKS STILL BE USED?

One Talking Point viewer asked whether his N95 masks that expired in 2017 could still offer him protection.

Ser sent two of them to ST Engineering’s mask production facility, along with other commonly used masks. There, the company tested how effective each mask was in filtering out airborne particles, including those similar in size to PM2.5.

The viewer’s masks achieved 99 per cent filtration efficiency, exceeding the 95 per cent requirement for N95 masks. By contrast, another N95 mask that expired in 2022 was at 93 per cent, below the required standard.

ST Engineering’s head of respiratory protection, Jerome Lee, said manufacturers may design masks that exceed filtration requirements to take account of deterioration over time. Masks stored in cool, dry conditions may also retain their filtration capability even years after expiry.

But he advised against using expired masks, as their performance can no longer be guaranteed and the amount of degradation “isn’t something you can observe using your naked eye”.

Talking Point also found that a surgical mask filtered out 67 per cent of the test particles, compared with 95 per cent for a KF94 mask and 98 per cent for new N95 masks.

Even an efficient mask offers less protection, however, if it does not fit snugly, Lee cautioned. Surgical masks, in particular, are not designed to be sealed tight.

He recommended discarding masks with damaged straps, deteriorated nose pads or other signs of wear.

4. WHY DO DIFFERENT WEBSITES HAVE DIFFERENT READINGS?

Some viewers asked why air quality readings on the National Environment Agency (NEA) website differed from those on international websites.

Ser compared a one-hour PM2.5 reading of 164 on the NEA website with a reading of 214 on the World Air Quality Index (AQI) website. “That’s quite a disparity. Why is that so?” she asked.

Natasha Jamali, principal scientific officer in the NEA’s environmental quality monitoring department, said some third-party websites use different data sources, including the NEA’s readings as well as low-cost sensor data from individuals and private organisations.

These sensors may not be calibrated as frequently as NEA’s analysers, and their readings can be affected by humidity and temperature. “More data may not necessarily be better because it depends on the quality of these data sources,” she said.

Calculations based on the AQI, developed by the United States Environmental Protection Agency, are also different from Singapore’s method of calculating PM2.5 readings, so the numbers are “not directly comparable”, she added.

As for how to use the NEA readings, she advised looking at the one-hour PM2.5 reading for the most recent indication of air quality before heading out or not.

The 24-hour Pollutant Standards Index, meanwhile, indicates the overall air quality over the past day. It measures six pollutants including PM2.5 and is used for health advisories and planning activities.

For next-day activities, Singaporeans can refer to the NEA’s air quality forecast, which also takes into account weather conditions and regional haze.

5. WHAT IS THE IMPACT OF EXERCISING OUTDOORS?

Despite the lingering haze, some people are exercising outdoors. One runner told Talking Point he came from an ActiveSG gym where all the treadmills were occupied. Another said: “I don’t like running on treadmills.”

A cardiopulmonary exercise test showed how much more PM2.5 particles they could be inhaling outdoors.

Riding an exercise bike at mild intensity, Ser breathed in about 50 per cent more air per minute than at rest. This rose during moderate exercise to three times her baseline and to six times with maximal exertion.

Senior consultant cardiologist Peter Ting at the Harley Street Heart and Vascular Centre said athletes could breathe in 10 to 20 times more air during vigorous exercise.

His fellow doctor, Yang, estimated that Ser would have inhaled about 1.7 micrograms of PM2.5 per minute at rest and about 7 micrograms during intense exercise if she were outdoors, based on the PM2.5 reading at the time.

PM2.5 exposure can increase the risk of heart attack, particularly among the elderly and those with existing lung and heart conditions. “After about an hour,” Ting warned, “the risk already starts to go up.”

He advised those exercising outdoors to check the one-hour PM2.5 reading, reduce workout intensity and duration and avoid busy roads, where traffic adds to the pollution.

Yang said he would move exercise indoors once air quality reaches the unhealthy range — while continuing to monitor the PM2.5 reading as there could be indoor air pollution.

6. WHEN WILL THE HAZE END?

Singaporeans can expect some relief by mid-November, according to NTU climate researcher Wang Jingyu.

The assistant professor said the arrival of the northeast monsoon will change the prevailing winds; smoke from forest fires in Indonesia will no longer be carried to Singapore.

But there is a secondary haze season, typically from March to May, when hot and dry conditions can increase the risk of wildfires in the region, he highlighted.

7. COULD IT GET WORSE IN FUTURE?

Wang said scientists also expect future climate conditions to “be more El Nino-like”. This could reduce rainfall in Southeast Asia “significantly” and make forest fires harder to extinguish, increasing the likelihood of a similar haze episode recurring.

Whether it could get worse, however, also depends on countermeasures to control the haze. The Association of Southeast Asian Nations has created a roadmap aimed at achieving a haze-free region by 2030. Strengthening enforcement is one of the strategies.

In recent days, the NEA issued notices to 10 companies in Indonesia under the Transboundary Haze Pollution Act, followed by notices to 10 Singapore-based firms for the first time under the law.

Singapore has also offered Indonesia assistance with its firefighting efforts and in cloud seeding. For now, Singaporeans can only look ahead to the winds to change.

Watch this episode of Talking Point here. The programme airs on Channel 5 on Thursdays at 9.30pm.