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Air Quality


Air pollution refers to the presence of toxic chemicals or compounds in the air, which lower the quality of the air and pose a risk to health.

Poor air quality, also known as “haze” and “smog”, is a growing global health concern. The World Health Organization (WHO) estimates that over seven million deaths are caused by air pollution each year. Some groups may be more susceptible to air pollution, these include older adults, children and those with underlying health issues such as heart disease, chronic lung problems and asthma.

Haze is caused by dust, smoke and other pollutants that obscure the clarity of the sky. This happens when the air is relatively dry and when weather patterns do not allow pollutants to disperse.

Smog is a type of air pollutant derived from vehicular emissions and industrial fumes. These react in the atmosphere with sunlight to form secondary pollutants (noxious vapours, ground-level ozone and particles).   There are several systems used to measure air quality

Air Quality Index-Rating

The following are some of the air quality indexes or rating systems available globally.

Air Quality Index (AQI)

The United States developed AQI which links air quality measurements to health effects. Its AQI is based on five pollutants: ground-level ozone, particulate matter, carbon monoxide, sulphur dioxide and nitrogen dioxide. The higher the AQI, the greater the risk to health.

Many countries have based their AQI on the United States system. Australia's AQI uses the same five pollutants, but also incorporates a measure of visibility. Discover more about Australia’s AQI system used by its States and Territories, as well as air quality data via the Bureau of Meteorology (BOM) - here.

Air Quality Health Index (AQHI)

AQHI is used in Canada and was adopted by Hong Kong in 2013. It is designed to help understand the impact of air quality on health and helps decide when to reduce the time of exposure to air pollution by adjusting activity levels depending on the level of pollution.

Air Pollution Index (API)

API is used by Malaysia. It measures PM2.5, PM10, SO2, NO2, O3 and CO, with higher API values representing a greater risk to health.

Comprehensive Air-quality Index (CAI)

The scale is used in South Korea. Pollutants measures are sulphur dioxide (SO2), particulate matter (PM10), fine particulate matter (PM2.5), nitrogen dioxide (NO2), carbon monoxide (CO) and ozone (O3). The scale ranges from 0 to 500, and higher values indicate a greater negative impact on health.

Pollutant Standards Index (PSI)

This system is being used by Singapore to measure air quality. PSI was developed by the United States Environmental Protection Agency (USEPA) to measure pollution levels for six air pollutants: PM2.5, PM10, SO2, NO2, O3 and CO. It uses a scale of 0-300+ to measure air quality and classifies air pollution levels into good, moderate to unhealthy and hazardous.

Each index/rating system provides its own health messages for the general public and “at risk” individuals. The following are examples two (2) examples - Canada’s AQHI and South Korea’s CAI.

Air Quality Health Index (AQHI)

Health Risk 

Air Quality
Health Index 

Health Messages

General Population

At Risk Population*


1 - 3

Ideal air quality for outdoor activities.

Enjoy your usual outdoor activities.


4 - 6

No need to modify your usual outdoor activities unless you experience symptoms such as coughing and throat irritation.

Consider reducing or rescheduling strenuous activities outdoors if you are experiencing symptoms.


7 - 10

Consider reducing or rescheduling strenuous activities outdoors if you experience symptoms such as coughing and throat irritation.

Reduce or reschedule strenuous activities outdoors. Children and the elderly should also take it easy.

Very High


Reduce or reschedule strenuous activities outdoors, especially if you experience symptoms such as coughing and throat irritation.

Avoid strenuous activities outdoors. Children and the elderly should also avoid outdoor physical exertion.

* People with heart or breathing problems are at greater risk. Follow your doctor's usual advice about exercising and managing your condition.

Comprehensive Air-quality Index (CAI)


Air Quality Index 

Health Messages



A level that will not impact patients suffering from diseases related to air pollution.



A level which may have a meager impact on patients in case of chronic exposure.



A level that may have harmful impacts on patients and members of sensitive groups (children, aged or weak people), and also cause the general public unpleasant feelings.

Very Unhealthy


A level which may have a serious impact on patients and members of sensitive groups in case of acute exposure, and that even the general public can be weakly affected.


A level which may need to take emergency measures for patients and members of sensitive groups and have harmful impacts on the general public.


Limiting exposure to polluted air as much as possible is the best way to avoid health problems. The higher the level of pollution, the more important this becomes.

Protect against poor outdoor air quality

  • Stay indoors and keep doors and windows closed.

  • Use an air conditioner in “recirculate” mode if possible.

  • Consider using an air cleaner.

  • Reduce or avoid outdoor physical activities altogether.

    • Young children, older adults and people with underlying health issues, such as chronic bronchitis, emphysema, and asthma and pregnant women are considered to have higher chances of getting sick (high-risk group), hence they should be especially vigilant about minimising exposure.

  • When going outdoors, consider wearing a particulate respirator (N95 mask).

  • If air quality is predicted to reach hazardous levels on multiple consecutive days, people in the high-risk group may want to consider moving temporarily to a location with better air quality.

N95/P2 Respirators

Particulate respirators, such as an N95 (or P2), are designed to filter out small particles from the air. They filter out at least 95% of airborne particles, down to a fraction of a micron (μm), and so may provide some protection against particulate matter. They do NOT prevent inhalation of noxious gases and vapours. Respirators need to be “fit tested” as they should form a seal against the wearer's face, and air should not leak around the edges. They must be worn correctly to provide protection.

⚕️ A doctor should be consulted for an individual recommendation, particularly if there are underlying health conditions.

More Information

Discover more about Air Quality and Health at the following sites:

🇺🇸 United States

🇦🇺 Australia

🇳🇿 New Zealand

🇪🇺 European Environment Agency (EEA)

🇬🇧 United Kingdom

🇨🇦 Canada

🌐 The Center for Disease Control & Prevention (CDC)

🌐 World Health Organization (WHO)

(info) International SOS

General Travel Advice Disclaimer - here.

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