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​What are the key air pollutants of concern?

The key air pollutants of concern include particulate matter (PM), sulphur dioxide, ozone, nitrogen dioxide and carbon monoxide. Short term exposure (i.e. continuous exposure to unhealthy daily average PSI levels over a period of a few days) to these air pollutants can cause respiratory symptoms and aggravate existing heart or lung disease. Exposure to particulate matter and sulphur dioxide may also cause irritation of the eyes, nose and throat in healthy individuals.

In Singapore, the main air pollutant in the event of haze is particulate matter (PM).

What is the short term effect of the haze on my health?

Among healthy individuals, short term exposure (i.e. continuous exposure to unhealthy daily average PSI levels over a period of a few days) to high levels of haze particles may cause irritation of the eyes, nose, and throat in healthy individuals.  Such irritation resolves on its own in most cases.

Haze particles can affect the heart and lungs, especially in people who already have chronic heart or lung disease e.g. asthma, chronic obstructive pulmonary disease (COPD), or heart failure.

There may be up to 1-3 days of time between exposure to haze and health effects/ symptoms.

What are the long term effects of the haze?

Singapore is not affected by the haze throughout the year. Any exposure is short-term in nature (i.e. continuous exposure to unhealthy daily average PSI levels over a period of a few days) and such exposure may vary from year to year.  As international studies are based on long term exposure to air pollution, there is little robust data on the longer-term effects of short-term exposure to haze like the pattern seen in Singapore.

Studies have shown that persons living overseas with continuous exposure over several years to high ambient pollution from fine particles (i.e. particulate matter 2.5 (PM2.5); particles smaller than 2.5 micrometres), may have a higher risk of (i) cardiovascular effects, such as heart attacks, (ii) reduced lung development, as well as (iii) the development of chronic respiratory diseases, such as asthma, in children.

What is the revised Pollutant Standard Index? How is it different from PSI reporting last year?

The new, integrated air quality reporting index incorporates PM2.5 in addition to sulphur dioxide (SO2), particulate matter (PM10), nitrogen dioxide (NO2), carbon monoxide (CO), and ozone. Previously, health advisories issued by the Government were based on both 24-hour PSI and 24-hour PM2.5, whichever was worse. Under the new air quality reporting system, the health advisory will be based on the new 24-hour PSI as it now directly takes into account PM2.5.

Why is the health advisory based on 24-hour PSI, rather than the 3-hour PSI? Why does Singapore calculate the Particulate Matter (PM) in air pollution based on the 24-hour measurement? Why not use sub-daily measurement?

The health impact of exposure to particulate matter in the air depends on the concentration and duration of the exposure, as well as the health status and level of activity of the individual. The health advisory is based on the 24-hour PSI (incorporating 24-hour PM2.5 concentration), as most scientific studies on the health effects of short-term exposure to PM use 24-hour averages, and have demonstrated good links with 24-hour PM averages. The use of 24-hour averages for PM is also consistent with international guidelines, such as the US Environmental Protection Agency’s (EPA) National Ambient Air Quality Standards and the World Health Organization’s Air Quality Guidelines. Fewer studies have investigated shorter (sub-daily) exposure timeframes. In fact, a US EPA study in 2011 concluded that there was insufficient basis to establish a national standard with a shorter-than-24 hour averaging time. MOH will continue to monitor research in this area.

Which groups of people are more sensitive to haze?      

In general, children, elderly, and people with chronic lung disease, heart disease are more sensitive to the health effects of haze, and should adopt the preventive measures in the MOH health advisory when air quality is poor. Individuals are advised to consult their doctor should they develop breathing difficulties. In addition, it is advised that pregnant women reduce exposure to haze for the health of their unborn baby.

What is MOH’s advice to the public?

The public is recommended to adhere to the MOH haze health advisory (Annex A). In most cases, it is still safe to carry on with outdoor activities. However, do drink plenty of water to stay well hydrated.  Individuals with existing chronic heart and lung conditions should ensure that your medications are on hand and readily available.

Is the health advisory applicable to everyone?

While the health advisory provides generic precautionary advice, individual reactions to pollutants may vary. For instance, some vulnerable people, such as those with heart and lung conditions, may experience increased symptoms at PSI levels below 100. Such individuals are advised to be cautious and seek appropriate medical attention as needed.

How will the haze impact patients in nursing homes and subsidised wards with natural ventilation?

These patients are indoors and sedentary. The healthcare institutions, such as hospitals and nursing homes, will monitor patients closely, and ensure ample circulation of clean air indoors.

Where can I get more information on haze?

Please refer to the following websites:

For FAQS on use of masks and availability of masks, please refer here.

ANNEX A

MOH HEALTH ADVISORY FOR THE GENERAL PUBLIC (17 March 2014)

The health impact of haze is dependent on one’s health status (e.g. whether one has pre-existing chronic heart or lung disease), the PSI level, and the duration and intensity of outdoor activity. Reducing outdoor activities and physical exertion can help limit the ill effects from haze exposure. Persons who are not feeling well, especially the elderly and children, and those with chronic heart or lung conditions, should seek medical attention.

24-hour PSI

Healthy persons

Elderly, pregnant women, children

Persons with chronic lung disease, heart disease

≤100
(Good/Moderate) 

Normal activities

Normal activities

Normal activities*

101 – 200
(Unhealthy)

Reduce prolonged or strenuous outdoor physical exertion

Minimise prolonged

or strenuous outdoor physical  exertion

Avoid prolonged or strenuous outdoor physical  exertion

201 – 300
(Very Unhealthy) 

Avoid prolonged or strenuous outdoor physical exertion

Minimise outdoor activity

Avoid outdoor activity

>300
(Hazardous)

Minimise outdoor activity

Avoid outdoor activity

Avoid outdoor activity

*Although the general advice to the public when the air quality is good or moderate (PSI≤100) is to maintain normal activities, vulnerable persons, especially those with chronic heart and lung conditions, who develop symptoms or feel unwell should seek medical attention promptly.

Prolonged = continuous exposure for several hours 

Strenuous = involving a lot of energy or effort

Reduce = do less

Minimise = do as little as possible

Avoid = do not do.