API or PSI? How Malaysia and Singapore Measure Haze

Malaysia's API and Singapore's PSI are two different indices that share the same band names, which is exactly why the difference gets missed. Both run on a 24 hour average of six pollutants and both take the highest single sub-index as the headline number. They part company above 300, where Malaysia has a band Singapore does not.

TYGRON® is a tiger milk mushroom (Lignosus rhinocerus) functional food developed by ORGANO and Fungitech Sdn Bhd in Malaysia and formulated in Australia, and every haze season families with relatives on both sides of the Causeway send us the same message: the numbers do not match. They are not supposed to.

What is the API, and what does it actually measure?

The Air Pollutant Index is published by Malaysia's Department of Environment. It covers six criteria pollutants: PM2.5, PM10, carbon monoxide, ozone, sulphur dioxide and nitrogen dioxide. A sub-index is calculated for each, and the highest single sub-index becomes the API.

That is the detail most people get wrong. An API of 150 does not mean the air is moderately bad across the board. It means one pollutant, usually PM2.5 during haze, reached 150 on its own scale. The index reports the worst thing in the air, not the average.

The Department of Environment's own table labels the bands under a column headed "Status", and the labels run: 0 to 50 Good, 51 to 100 Moderate, 101 to 200 Unhealthy, 201 to 300 Very Unhealthy, above 300 Hazardous, above 500 Emergency.

What is the PSI, and how is it different?

Singapore's Pollutant Standards Index is published by the National Environment Agency and, on paper, works almost identically. NEA describes it plainly: "The PSI is computed based on the 24-hour average of concentration levels of 6 pollutants namely, particulate matter (PM 10 ), fine particulate matter (PM 2.5 ), sulphur dioxide (SO 2 ), nitrogen dioxide (NO 2 ), ozone (O 3 ), and carbon monoxide (CO). A sub-index value is computed for each pollutant based on the pollutant's ambient air concentration. The highest sub-index value is then taken as the PSI value."

Same six pollutants. Same highest-sub-index method. Same 24 hour window. PM2.5 was the last one added, in April 2014, which is when the PSI became a meaningful haze number.

NEA reports the PSI for five regions, North, South, East, West and Central, which is why a Singaporean quotes a different figure depending on where they live. NEA also publishes a separate one hour PM2.5 reading, the faster-moving number people watch.

Do the two scales mean the same thing at the same number?

Up to 300, yes. Above 300, no.

The band names are identical across the whole range either country realistically sees. That is the trap: because the words match, people assume the indices are interchangeable. They are two national systems sharing a vocabulary.

Why does Malaysia have a band Singapore does not?

Because Malaysia sits closer to the source. Haze reaching Singapore has travelled further and dispersed more, while parts of Sarawak sit almost on top of the fires.

Malaysia's Emergency band above 500 is not a stronger warning about air. It is a different kind of instruction: the Department of Environment's advice at that level is to follow orders from the National Security Council and announcements in the mass media. Air quality stops being personal precaution and becomes civil emergency.

Singapore's ladder stops at Hazardous, and that band is open ended: a PSI of 520 is still Hazardous. Singapore does not lack a band above 500, it lacks a sixth band. So never apply the word Emergency to a Singapore reading.

Why does the app on your phone disagree with the government?

Because most apps are not showing you the API or PSI at all.

NEA addresses this directly: "While Singapore had referenced the USEPA AQI system, it is not identical. Air quality readings or indices provided by other websites, such as aqicn.org, adopt other methods of computing the index and are not comparable with the 24-hr PSI."

Third-party apps usually publish a US-style AQI, often hourly rather than over 24 hours, sometimes from sensors that are not official stations. That does not make them useless. It makes them a different measurement, and comparing an app's 180 against a government 120 and calling someone a liar is a category error.

We run into this ourselves. Our Breathe Easy page pulls live figures from the World Air Quality Index Project so families see both countries in one view, and we label those readings unvalidated for exactly this reason. For a decision that matters, go to the source.

Which number should you actually act on?

The official one for the country you are standing in, and the band rather than the digit.

At 101 to 200 both countries call it Unhealthy. Malaysia's Department of Environment advises limited outdoor activities for high risk people, meaning those with heart and lung complications, and asks the public to reduce extreme outdoor activity. That is the practical trigger: a properly fitted respirator earns its place, and outdoor exercise moves indoors.

At 201 to 300, Very Unhealthy, the advice sharpens. The Department of Environment advises that old and high risk people stay indoors and reduce physical activities, and that people with health complications see a doctor.

A useful habit is to check twice a day, once before the school run and once in the late afternoon, acting on the band rather than on whether the sky looks bad. Visibility and smell are unreliable: NEA notes a burning smell is usually, but not always, accompanied by a rise in the readings.

What the numbers do not tell you

Neither index tells you about your own house. Both are outdoor measurements from fixed stations that may be kilometres from where you sleep, averaged over a full day, and indoor air in a naturally ventilated Malaysian home tracks it more closely than most people expect.

Neither tells you about cumulative exposure. A season bouncing between 90 and 130 never produces a dramatic headline, and it is still a long stretch of degraded air. The index is a daily decision tool, not a health record.

The habit families reach for through a long season

Checking a number is a decision. What families ask us for is what runs underneath those decisions, on the days the reading is unremarkable and the season is still long.

Tiger milk mushroom has been used in Malaysia for generations for respiratory complaints, a heritage recorded across more than 400 years, and that tradition is why TYGRON® is a daily sachet rather than a seasonal fix. Most people see improvement within the first few days. Some customers even notice a difference after just one to two days, and most report a significant improvement in their lung wellness after a few weeks of daily use. Individual experiences vary.

Read the band, not the headline

Two indices, one shared vocabulary, one real divergence above 300. The band name tells you what to do; the country tells you whose band it is.

Next in this series: the daily routine that works when Klang Valley readings climb, which mask actually works for haze, and lung protection through the 2026 season.

Frequently asked questions

Is API the same as PSI?

No. They are two separate national indices: Malaysia's Air Pollutant Index from the Department of Environment and Singapore's Pollutant Standards Index from the National Environment Agency. They use the same six pollutants, the same 24 hour averaging and the same highest-sub-index method, and their band names match up to 300, but Malaysia carries an extra Emergency band above 500.

At what API reading should my family stay indoors?

From 101 the band is Unhealthy, and Malaysia's Department of Environment advises limited outdoor activities for high risk people, meaning those with heart and lung complications, and asks the public to reduce extreme outdoor activity. From 201 the band is Very Unhealthy and older people and anyone with heart or lung trouble should be indoors and avoiding exertion.

Why does my air quality app show a different number from the government?

Because most apps publish a US-style AQI rather than the API or PSI, often on a one hour basis instead of 24 hours. NEA states that indices from other websites "adopt other methods of computing the index and are not comparable with the 24-hr PSI". Treat an app as an early warning and the official figure as the decision.

Does a high API mean every pollutant is high?

No. Both report the highest single pollutant sub-index, not an average. During haze that is almost always PM2.5, and the remaining five may be perfectly ordinary. The index tells you about the worst thing in the air rather than the overall mix.

Is Singapore's Hazardous the same as Malaysia's Hazardous?

The band name is the same and begins above 300 in both countries. The difference is that Singapore's Hazardous is open ended, so a PSI of 520 is still Hazardous, while Malaysia adds a sixth band, Emergency, above 500. At that Malaysian level the advice moves from personal precautions to following the National Security Council, so the two ladders are not equivalent at the top end.

About TYGRON®

TYGRON® by ORGANO is a tiger milk mushroom functional food made for Malaysian and Singaporean households. It is formulated in Australia and manufactured in Malaysia, and it holds the Malaysia Book of Records for the highest 1,3/1,6 beta-glucan content in Malaysia. 1,3/1,6 beta-glucan is the most important active compound and quality benchmark in tiger milk mushroom, and a higher content signals greater potency and quality.

TYGRON® is formulated in Australia, designed by our Sydney-based team (Fungitech Australia Pty Ltd) to one of the world's most stringent functional-food standards, then manufactured in Malaysia under GMP, HACCP and Halal-certified conditions.

Why TYGRON® is formulated in Australia →

About the author

This article was written and reviewed by Boey Tze Zhou, Founder and CEO of ORGANO. Boey holds a Bachelor of Agricultural Science (First Class Honours) from Universiti Putra Malaysia and has completed Stanford University's Introduction to Food and Health and the University of Minnesota's Integrative Health and Medicine specialization (including Herbal Medicine) through Coursera. With over two decades in functional-mushroom cultivation, he developed the TMM365+ slow-grown method behind the Malaysia Book of Records beta-glucan certification held by Fungitech Sdn Bhd. He is an international speaker on functional mushrooms, invited to China International Mushroom Day 2025 and other mushroom-science events across the Asia-Pacific, and was named one of the Top Ten Outstanding Penang Youth (TOPY) in 2024. Read more about the founder

Sources

• Department of Environment Malaysia, General Information of Air Pollutant Index
• National Environment Agency Singapore, Air Pollution FAQs

This article is general information, not medical advice. TYGRON® is a functional food. If symptoms are severe or persistent, please see a doctor.